chapter 2 force and motion (answer)

8/17/2019 Chapter 2 Force and Motion (Answer)

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JPN Pahang Physics Module Form 4

Chapter 2 : Force and Motion

1

2. FORCE AND MOTION

2.1 ANALYSING LINEAR MOTION

Distance and displacement

1. Types of physical quantity:

has only a magnitude(i) Scalar quantity: ………………………………………………………………….has both magnitude and direction

(ii) Vector quantity: …………………………………………………………………

2. The difference between distance and displacement:length of the path taken

(i) istance: …………………………………………………………………………distance of an object from a point in a certain direction

(ii) isplacement: ……………………………………………………………………

!. istance always lon"er than displacement.

#. $%ample: The followin" dia"ram shows the location of &ohor 'ahru and esaru.

ou can trael by car usin" e%istin" road ia *ota Tin""i+ or trael by asmall plane alon" strai"ht path.

,alculate how far it is from &ohor 'ahru to esaru if you traeled by:

a. The car

b. The plane*ota Tin""i

#1 -m ! -m

Solution:&ohor 'ahru

/0 -m esaru

a. by car #1 !

3# -m

b. by plane /0 -m

The path traeled by the plane is shorter than traelled by the

car.

So+ istance 3# -m

isplacement /0 -m

4ands5on 6ctiity 2.2 p" 10 of the practical boo-.

7dea of distance and displacement+ speed and elocity.

Speed and velocity

! Speed is ..……the

…d

…ist

…an

…ce

…tra

…"e

…le

…d p

…er

…un

…it

…tim

…e

…or

…ra

…te

…of

…ch

…an

… ge

…of

…di

… sta

…nc

…e

…………

2! Velocity is: ..…the

… sp

…ee

…d

…in

…a g

…i"

…en

…dir

…ec

…tio

…n

…

or …

ra…

te…

of…

ch…

an…

ge…

of …

di…

spl …

ac…

em…

en…

t #

………...

$!6era"e of speed: …

to…

ta…

l d …

ist …

an…

ce…

tra…

"e…

le…

d%…

s & …

m'…

%…

"…

(

s……

m…

s………………………


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2

#

time taken% t &s' t

4!6era"e of elocity:

d …

isp…

la…

cem…

e…

nt%…

s…

&m…

' %……

" (……

s m…

s…………………………………... )ime taken% t &s' t


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2. 6cceleration is+

*!$%ample:

6n aero plane flies from 6 to '+ which is located !00 -m east of 6. 8pon reachin" '+ the

aero plane then flies to ,+ which is located #00 -m north. The total time of fli"ht is #hours. ,alculate

i. The speed of the aero plane

ii. The elocity of the aero plane

Solution:

6 !00 -m

C

#00 -m

'

,

#00 -m

i! +peed ( ,istance

)ime

( $-- . 4--4

( /* km h#

ii! "elocity ( displacement

time

&,etermine the displacement denoted

by 0C and its direction'

= . 500 .

6 '

!00 -m

4( 2* km h

#&in the direction of -*$

- '

Acceleration and deceleration

1. Study the phenomenon below9

0 m s51 20 m s

51

)he "elocity of the carincreases!

#0 m s51

bseration: ………………………………………………………………………………the rate of change of "elocity

………………………………………………………………………. Final "elocity 1 initial "elocity

Then+ a Or, a = v – u

)ime of change t !. $%ample of acceleration9

t 2 s t 2 s

6 ' ,


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0 m s51 20 m s51 #0 m s51


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. . . . . . . .

.%. . . . . . .

. . .……………………………………………………………………………………..

. . . . .

. . . . . . . .

JPN Pahang

20 – 02

= 10 m s-2

Physics Module Form 4Chapter 2 : Force and Motion

,alculate the acceleration of car9

i' from 6 to ' a 0 ( 2- 1 - ( - m s#2

2

ii' ;rom ' to , a C ( 4- 1 2- ( - m s2

3hen the "elocity of an object decreases% n calculations% a 3ill #. eceleration happens ...…………………………………………………………………

be negati"e………………………………………………………………………………………………

. $%ample of deceleration9

6 lorry is moin" at !0 m s51+ when suddenly the drier steps on the bra-es and it stop

seconds later. ,alculate the deceleration of lorry.

0ns3er : " ( - m s# % u ( $- m s# % t ( * s

Analyzin o! motion

)hen % a ( - 1 $- ( #5 m s#

2 *

!


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0cceleration% then deceleration


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# s ( ;--

a (

(

(

(

u

.etermination of elocity

. . . . . . .

.……………………………………………………………………………………..

(i)

2!5 cm / 9 -!-2 ( -!4 s

displacement ……………………… time ………………………………..

Velocity+ 2!5 (


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s ( ;--

( ;-- m


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;i"ur 2.1e

$%ample 2 : 6 an that is traelin" with elocity 1/ m s51 decelerates until it comes to rest.

7f the distance traeled is ? m+ calculate the deceleration of the an.

gi"en : u ( 5 m s# % " ( -&rest' % s ( ; m a (

= "2 ( u2 . 2 as

-2 ( 5 2 . 2 a&;'

a ( #5 ms#2

E%ercise 2.&

1. ;i"ure 2.1 shows a tape chart

consistin" of 5tic- strip. escribe


10/108

/

s final ( sinitial 1 s

( ;- 1 5-

( 2- m


11/108

Araph analysis:

ANA'(SIN) MOTION )RA*+S

0m 100m 200m !00m #00m 00m displacement

0s 10s 20s )he ob! je

0cst mo"es 3

#i0t sh uniform "

e0lo

scity

for tt im

seeconds!

0fter t secoinnd t sh %eth foer ombo je f c g t r r ae ptuhr cna sl t l oed or aig minot & ir oen"e g r r sae p 'h3 s ith

The data of the motion of the car can beu pnr if eosr emnte"de…loc…ity…………………………….

T"e displacement,time )rap" )otal displacement is 8ero

a' displacement (m) Araph analysis:

… ?…nr ia f …o pr h…mis…d 6is…u pala…d crae…mtic…en fo…t r am…ll t …he…tim…e…………………………

!

…? ,…r ia s… p phla… g cr e…amd …eiennt …t in…(cr …e"ael …

soec s…it 3 y…it (h…-ti…me…!

………………………

s) …) …?hr e…ao p…bh je… g cr t a..id . s…ie st n…at tii…onnc…

r aer a… y soe…r s iu… snni… f oot r …mm…oly"…ing …………………

b'displacement (m)

)he object mo"es 3ith increasing "elocity 3ithuniform acceleration!

… ,…is. p.…la…cem…e…nt …inc…re…ase… s …un…

ifo…rm…ly…………………………

…?…ra… ph… g …ra…die…nt …is… fi9…

ed ……………………………………… time (s)…) …he…o.b… je…ct …

mo…"e…3…ith…un…ifo…rm…"…elo…ci…ty ………………………

c' displacement (m) Araph analysis:

…….……………………………………………………………

…………………………………………………………………

time (

time (s)


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..…………………………………………………………………

d' isplacement (m) Araph analysis:

…………………………….………………………………………

……………………………………………..………………………

time (s) ………………………………………………………………………

…………………………………………………………………


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e' displacement (m) Araph analysis:

…?r

…ap

…h i

… s 6

…ua

…dr

…at

…ic

… for

…m!

………………………………..

… ,i… spl …ac…em…en…t i…nc…rea… se… s 3…it …h

t …im…e! ……………………..

…?…rap…h… gr …ad …ien…t d …ec…re…ase… s u…n

fo…rm…ly …………………..

time (s)

…)h…e o…bj…ect …m…o"…es…3i…th…de…cre…as

in… g "…el …oci…ty%…3…ith…un…ifo…rm..deceleration!

f' displacement (m) Araph analysis:

6 '@0

…( u

…ni

… for

…m

…"e

…lo

…cit

… y &

… po

… siti

…"e

… 1

…mo

…"e

…a…

hea…

d'……………..

…… 0

…

…(

…"el

…oc

…ity

…is

… 8e

…ro

…&re

… st

… '

………………………..

, time (s)

T"e velocity,time )rap"

… C

…(

…u

…nif

…or

…m "

…el

…oc

…ity

…&n

…eg

…ati

"e…

1…

re"…

er …

se'………………

a) > m s51 Araph analysis:

No cha…ng …e …in …"e…loc…

ity………………………………………

…..

…..

Aero gradient the object mo"es 3ith a constant "elocity or

the acc…el …era…ti…on…is… 8e…ro!

……………………………………

)he area under the graph is e6ual to the displacement of th

mo"ing object :…………… s (…"… 9 …t

b) …> m s51 Araph analysis:

…………………………………

…..

…

ts "e…

lo…

cit …

y i…

ncr …

ea…

se…

s u…

nif …

or …

ml …

…………..……………)he graph has a constant gradient

)he…

ob…

jec…

t m…

o…

"es…

3…

ith…

a…

un…

ifo…


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rm

…a

…cc

…ele

…ra

…tio

…n

…………

)he area under the graph is e6ual to the displacement%

s of the mo"ing object : s ( > & " 9 t'

c) (m s51) Araph analysis:

)he object mo"es 3ith a uniform acceleration for t s…………………………………..…………………. 0fter t s% the object decelerates uniformly &negati"e gradien………………………………………………………until it comes to rest!………………………………………………………)he area under the graph is e6ual to the displacement of the

t1 t2 t (s)mo"ing object : s ( > "t 2


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R

0 t>

d) (m s51) Araph analysis:)he shape of the graph is a cur"e...…………………………………..………………..

ts "elocity increases 3ith time!………………………………………………

)he gradient of the graph increases!……..

t (s)

)he object mo"es 3ith increasing acceleration!………………………………………………………

)he area under the graph is e6ual to the total displacement oth

…e

…mo

…"i

…ng

…ob

… je

…ct!……………………………………

.……………………………………………………...

)he shape of graph is a cur"ee) (m s51) Araph analysis:

ts "elocity increases 3ith time!………..…………………………..………………..

)he gradient of the graph decreases uniformly!……….……………………………………

)he object mo"es 3ith a decreasing acceleration!………..

)he area under the graph is the total displacement of the

m…

o"…

in…

g o…

bj…

ect …

! ………………………………………

t (s) ………………………………………………………

E%amples ………………………………………………………

1. s>m,alculate:5&i' Velocity o?ie"r en B:++ C@P = (an2d- = mS + @B ( 2- m + @

- m

20 P Q

&ii'isplacement

Solution :

+ @+ ( # - m

t @P ( 2 s t PB ( $ s t B ( 2 s t + ( s

20 −1 0 − 20 −1

10&i' D @P (

2

=10m

s

D B ( = −10ms2

O R D +(

-10 −

0= −10ms

−1

0 2 # / ? t>s

1

&ii' + ( #-m

510 S

2. >m s51

10,alculate:5

(i) acceleration+a oer B+ BC and C=

(ii) isplacement

P Q ?i"en : D @ ( - m s# % D P ( - m s

# %Solution :D B ( - m s

# D ( - m s#

t @P ( 4 s t PB ( 4 s t B ( 2 s10 − 0 − 10 −10

0 2 #


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/ ? 1 &i' a@P(

s

4

aB(

= 2.5ms2

a PB(4

- − -= −*!- ms

−2

2

= 0

ms−2

? 1&ii' + (

(4

2

+10)

(10)

= 70.0m


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10

0

510

2 #t>s

t>s

10

0

510

2

#

O

E%cercise 2.2

1. (a) s>m (b) s>m (c) s>m

t>s

;i"ure 2.21

escribe and interprDte the motion of a body which is represented by the displacement

time "raphs in ;i"ure 2.21a' )he body remains in rest * m at the back of initial point

b' )he body start mo"e at - m infront of the initial point% then back to initial

point in 2 s! )he body continue it motion back3ard - m!!)he body mo"e 3ith uniform "elocity!

c' )he body mo"e 3ith inceresing it "elocity!

2. escribe and interpret the motion of body which is represented by the elocity5time

"raphs shown in fi"ure 2.22. 7n each case+ find the distance coered by the body and itsdisplacement

(a) >m s51 (b) >m s51

t>s t>s

;i"ure 2.22

&a' )he body mo"e 3ith uniform "elocity % * m s# back3ard!

&b' )he body start it motion 3ith - m s# back3ard and stop at initial point in 2 s% then continue it motion for3ard 3ith increasing the "elocity until

- m s# in 2 s!

3

5

5


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……………………...

…………………………….

-NDERSTANDIN) INERTIA

Idea o! inertia 0 pillion rider is hurled back3ards 3hen the motorcycle starts to mo"e!

1. ……………………………………………………………………………………………… us passengers are thrust for3ard 3hen the bus stop immediately!

2. ……………………………………………………………………………………………… Earge "ehicle are made to mo"e or stopped 3ith greater difficulty!

!. ………………………………………………………………………………………………

4and5on actiity 2. in pa"e 1? of the practical boo- to "ain an idea of inertia

#. Eeanin" of inertia :)he inertia of an object is the tendency of the object to remain at rest or% if mo"ing% to…………..………………………………………………………………………………….

continue its uniform motion in a straight line………………………………………………………………………………………………

Mass and inertia

1. =efer to fi"ure 2.1# of the te%t boo-+ the child and an adult are "ien a push to swin".

&i'which one of them will be more difficult to be moed

0n adult

&ii'which one of them will be more difficult to stopF

0n adult

2. The relationship between mass and inertia : ……………………………….………………)he larger the mass% the larger its inertia!……………………………………………..

ha"e the tendency to remain its situation either at rest or in!. The lar"er mass ………………………………………………………………………….

mo"ing!………………………………………………………………………………………………

E!!ects o! inertia 0pplication of inertia

1. Bositie effect : ………………………………………………………………………… ,rying off an umbrella by mo"ing and stopping it 6uickly!

(i) ……………………………………………………………………………………… uilding a floating drilling rig that has a big mass in order to be stable and safe!

(ii) ………………………………………………………………………………………)o tight the loose hammer

(iii) ………………………………………………………………………………………

e should take a precaution to o"oid the effect!2. Ge"atie effect : …………………………………………………………………………. ,uring a road accident% passengers are thrust for3ard 3hen their

(i) ……………………………………………………………………………………...car is suddenly stopped!

…………………………………………………………………………… Passengers are hurled back3ards 3hen the "ehicle starts to mo"e and are hurled for3ard

………..3hen it stops immediately!

(ii) ……………………………………………………………………………………… 0 person 3ith a hea"ierGlarger body 3ill find it mo"e difficult to stop his mo"ement!

0 hea"ier "ehicle 3ill take a long tim10e to stop!


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………………………………………………………………………………………

(iii) ………………………………………………………………………………………

………………………………………………………………………………………

(i) ………………………………………………………………………………………

E%ecise 2.

1. Hhat is inertiaF oes 2 -" roc- hae twice the inertia of 1 -" roc-F netia is the tendency of the object to remain at rest or% if mo"ing% to continue its uniform………………………………………………………………………………………………motion in a straight line!………………………………………………………………………………………………Hes% the inertia increase 3ith the mass increased!………………………………………………………………………………………………

2.

;i"ure 2+!

6 wooden dowel is fitted in a hole throu"h a wooden bloc- as shown in fi"ure 2.!1.

$%plain what happen when we

(a) stri-e the top of the dowel with a hammer+

0 3ooden block mo"e up of a 3ooden do3el!……………………………………………………………………………………… 0 3ooden block has inertia to remains at rest!………………………………………………………………………………………

(b) hit the end of the dowel on the floor.

)he 3ooden block mo"e do3n3ard of a 3ooden do3el!……………………………………………………………………………………… 0 3ooden block has inertia to continue it motion!……………………………………………………………………………………

ANA'(SIN) MOMENT-M Idea o!

moment$mit has momentum!

1. Hhen an obIect is moin"+ …...…………………………………………………………depends on its mass and "elocity!

2. The amount of momentum ...……………………………………………………………as the product of its mass and its "elocity% that is

Momentum% p ( m 9 " nit( kg m s#11


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mv

bb

!. Eomentum is defined…………………………………………………………………….

………………………………………………………………………………………………

Conservation o! moment$m

mg

m v v = 0b

bg

Momentum ( m "b b

Startin" position beforeshe catches the ball

(m m ) b "

vb&g

ecei"ing a massi"e

ball Momentum( &m .m '"

b g bIg

vg

" Momentum ( m

b bStartin" position m"

before she throws

the ball Momentum (# m "

)hro3ing a massi"e ball g g

T"e principle o! conservation o! moment$m / ………………………………………………… n t he absence of an e9ternal force% the total momentum of a system remains

……………………………………………………unchanged!

………………………………………………………………………………………………………)he colliding objects mo"e separately after collision!

1. $lastic collision .…………………………………………………………………………..

u1

m1 u2 2

m2 m1m2

12


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Momentum : mu . m2u2 ( m" . m2"2


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1!

'efore collision after collision

)he colliding objects mo"e together after collision!2. 7nelastic collision :………………………………………………………………………...

u1

m1 u2 0m2

1

m2

'efore collision after collision Momentum : mu . m2u2 ( &m . m2 ' "

)he objects in"ol"ed are in contact 3ith each other before e9plosion and are!. e%plosion : s

…ep

…ara

..t .e..d

…a…

fte…

r t …

he…

e9…

plo…

si…

on…

!

…………………………………………...

(m1 m2)+ u 0 1 2

m2

Momentu'

mef

:or

& em

e%. plos

mio

'nu (

m " # m " after e%plosion 2 " 2 2

$%ample 1 :

,ar 6 ,ar '

,ar 6 of mass 100 -" traelin" at !0 m s51 collides with ,ar ' of mass 30 -" traelin" at 20m s51 in front of it. ,ar 6 and ' moe separately after collision. 7f ,ar 6 is still moin" at 2 ms51 after co?lil"iseinon:+mdet(erm-i-nekg the eloc % iuty (of $,-amr ' s#after collision#.

Solution : 0

0

u ( 2- m s# % " ( =

% " 0 ( 2* m s

% m (


23/108

,ar 6 of mass 100 -" traelin" at !0 m s51 collides with ,ar ' of mass 30 -" traelin" at 20

m s51 in front of it. ,ar 6 is pulled by ,ar ' after collision. etermine the common elocity of ,ar 6 and ' after collision.

?i"en : m 0 ( -- kg % u 0 ( $- m s# % m (


24/108

Stationary obIect

3eight% 3 ( mg

FK

Idea o! !orce

1. Hhat will happen when force act to an obIectF Force can make an object………………………………………………………………………………………………

! Mo"e 2! +top the mo"ing ………………………………………………………………………………………………!. Change the shape of the object 4! 7old the object at rest

………………………………………………………………………………………………

Idea o! 1alanced !orces

1. 6n obIect is said to be in balance when it is:! n a stationary state

………………………………………………………………………………………………2! Mo"ing at uniform "elocity

………………………………………………………………………………………………

2. Stationary obIect Normal reaction% N

……………………………… e%planation : Magnitude ( but acts in an opposite………………………………………………direction to the 3eight!………………………………………………& object is in e6uilibrium '……….……………………………………..

…………………………………………

!. 6n obIect moin" with uniform elocity Normal reaction% N …………………………….. e%planation :

Frictional force Force% F Force % F ( Friction…..……………. …………… ……………………………………………..

………………..

esultant ( F 1 Friction……………………………

( - &object is in e6uilibrium'

3eight% 3 ( mg L9amples :……………………………………………..

!0 car mo"e at constant "elocity!……………………………… ………..…………………………………….

2!0 plane flying at constant "elocity!……………………………………

……….. ……………………………3hen it is mo"ing in acceleration!

………………..

esultant forceIdea o! $n1alanced !orces)he ball mo"e in acceleration

1. 0 body is said to be in unbalanced!!……………………………………………………because the forces act are not balanced! F

2. ……………………….. $%planation9 FK

F …………

……………………………………+o% the ball mo"e in F direction


25/108

………………………………………………

………………………………………………

……… …….. ………………………………………………

Relations"ip 1eteen !orces3 mass and acceleration 4F 5 ma6

L9periment 2!2 page 2

constant force.

1. =efer to the result of e%periment 2.2 and 2.!+it is found that a ∝ F 3hen m is constant and a ∝ Gm 3hen F is constant!……………………………………………………………………………………………)herefore% a ∝ FGm

……………………………………………………………………………………………… Fr …om a ∝ FGm%

………… F …

∝…m…a…………………………………………………………………………

…)h…ere… fo…re%… F …(…km…a ……k …(c…on… sta…nt …(…

…………………………………………………

……

………………………………………………………………………………………………

2. 1 newton (; 1 G) is defined as the force required to produce an acceleration of 1 m s52

(a1 m s52) when its actin" on an obIect of mass 1 -" ( m 1 -") F ( ma…………………………………………………………………………………………

!. $%ample 1 : ,alculate ;+ when a ! m s52 dan m 1000 -" F ( ma

F ( &---'

&$' F ( $---

N

$%ample 2 :m 2 -"m 2 -"

; 200 G; 200 G

E%ercise 2.7

So+


26/108

,alculatetheacceleration+a of anobIect.

F

(

ma

2

--

(

2

*

a

a (

;!-

ms#2


27/108



1. 6 trolley of mass !0 -" is pulled alon" the "round by horiJontal force of 0 G.

The opposin" frictional force is 20 G. ,alculate the acceleration of the trolley.

m ( $- kg % F ( *- N % F f ( 2- N % a ( =

F 1 F f ( ma % *- 1 2- ( $- a

a ( !- m s2

2. 6 1000 -" car is traellin" at @2 -m h51 when the bra-es are applied. 7t comes to a stop in

a distance of #0 m. Hhat is the aera"e bra-in" force of the carF

m ( --- kg % u ( /2 km h# % " ( -% s ( 4- m% F ( = Note : u ( /2 km h# (2- m s#

F ( ma% "2 ( u2 . 2as

( --- 9 *!- - ( 2-2 . 2a&4-'

( *---!- N a ( *!- m s2

ANA'(SIN) IM*-'SE AND IM*-'SI8E FORCE

Imp$lse and imp$lsive !orce)he change of momentum

1. 7mpulse is ……………………………………………………………………………….)he large force that acts o"er a short period of time during collision

2. 7mpulsie force is ………………………………………………………………………and e9plosion!

………………………………………………………………………………………………

!. ;ormula of impulse and impulsie force:

=efer+ ; ma

F ( m" 1 mu %

t

t is kno3n that a ( & " 1 u ' G t

)herefore% F ( m& " 1

u' t +o% Ft ( m" 1 mu % nit ( N s

Ft is defined as impulse% 3hich is the change in momentum!

Ft ( m" 1 mu nit : ne3ton &N' F is defined as impulsi"e force 3hich is the rate of change of momentum o"er the

short per *io& d -o ' f t #ime*&-'' -- ( -- N

( -- Ns $%ample 19 u

wall

7f 9 u 10 m s51 + 5 10 m s51 + m -" and t 1 s

7mpulse+ ;t and impulsie force+ ;

*&-' # *&-'' -- ( *- N $%ample 29 u

( -- Ns 2

mpulsi"e force % F∝

G t

1@

)herefore% F decreases 3hen the time of collision increases & refer to e9amples '


28/108

1?

Hall with a soft surface

7f 9 u 10 m s51 + 5 10 m s51 + m -" and t 2 s

7mpulse+ ;t and impulsie force+ ;

#. The relationship between time of collision and impulsie force.

………………………………………………………………………………………………

………………………………………………………………………………………………

E%ercise 2.9

1. 6 force of 20 G is applied for 0.? s when a football player throws a ball from the

sideline. Hhat is the impulse "ien to the ballF

F impulse ( Ft

( 2- 9 -!;

( 5!- Ns

2. 6 stuntman in a moie Iumps from a tall buildin" an falls toward the "round. 6

lar"e canas ba" filled with air used to brea- his fall. 4ow is the impulsie forcereducedF

! 0 large can"as bag 3ill increase the time of collision!

2! hen the time of collision increase the impulsi"e force 3ill decrease!

:EIN) A;ARE OF T+E NEED FOR SAFET( FEAT-RES IN 8E+IC'ES


29/108

Crash resistant door pillars

Anti-lock brakesystem A!"#

bumpers

$ein%orced passen&er compartment

'ead rest

(indscreen

Crumple )ones

*raction control Air ba&s

13

Safety features in vehicles

Importance o! sa!ety !eat$res in ve"icles

force 3ill be decreased!# )he passengerKs space made by the strength materials!

E%ercise 2.< : )o decrease the risk trap to the passenger during accident!

1. '# O y eues pina"n pahiyr sbicas g caot nt chee pitns+ f ero%n pt laoin f

d thae shmbiodaif r id caatniod nisnto frothnet o b f us path ssaetnh g eelprsto improe that

safety of passen"ers an:d 0wct i slla b seamcour sehcioonm f f oor rtt ah beleh.ead and bodyin an accident and thus pre"ents injuries to the dri"er and passengers!

# +hatter#proof 3indscreen

: Pre"ents the 3indscreen from shattering!

Sa!ety !eat$res Importance

Badded dashboard ncreases the time inter"al of collision so the impulsi"e force

produced during an impact is thereby reduced

=ubber bumper 0bsorb impact in minor accidents% thus pre"ents damage to the car!

Shatter5proof windscreen Pre"ents the 3indscreen from shattering

6ir ba" 0cts as a cushion for the head and body in an accident and thus

pre"ents injuries to the dri"er and passengers!

Safety seat belt

Pre"ents the passengers from being thro3n out of the car! +lo3s

do3n the for3ard mo"ement of the passengers 3hen the car stops abruptly Gsuddenly!

# )he absorber made

Side bar # i M n add oeor bs y

the soft ma

by the elastic materia P :re) "oenat b s sothr eb cthoellae p ff seect oo f f thime fr aocnt t & ahned nt baamcak no ' f d t uhr einc g ar it inmtoo"t ihne gtear si sael no g f ebr ucmom pe pr artment! 0lso gi"es good protection


30/108

………………………………...

fallin

g

the object is said to be free

is kno3n as acceleration due to gra"ity!

on the strength of the gra"itational field

! the gra"itational field of the

earth! is on the force of gra"ity!

as the gra"itational force acting on a kg mass!

! g ( F ! 3here% F : gra"itational force

m m : mass of an object

g (

-NDERSTANDIN) )RA8IT(that an object of mass kg 3ill e9perience a gra"itational force of

,arry out hands5on actiity 2.? on pa"e ! of the practical boo-.

Acceleration d$e to ravity.

! 6n obIect will fall to the surface of the earth because t pulled by the force of

gra"ity! +olution : F ( mg ( &5-a ' s & e


31/108

/. This means …………………………………………………………………………………

…………..

@. $%ample 1. ,an you estimate the "raitational force act to your bodyF

mass /0 -"+ " 3.? G -"51+ ; F

$%ample 2+

6 satellite of mass /00 -" in orbit e%periences a "raitational force of #?00 G. ,alculatethe "raitational field stren"th.

$%ample !+

6 stone is released from rest and falls into a well. 6fter 1.2 s+ it hits the bottom of the

well.(a) Hhat is the elocity of the stone when it hits the bottomF

(b) ,alculate the depth of the well.?i"en : u ( - ms# % t ( !2 s% a ( g (

&a' " ( = " ( u . at

( - . &

( !/5 ms#

&b' ,epth ( s ( = s ( ut . > at 2

( &-'&!2' . > &

( /!-*5 m

;ei"tas the gra"itational force acting on the object!

1. The wei"ht of an obIect is defined ……………………………………………………..

2. ;or an obIect of mass m+ the wei"ht can be calculate as :3eight% ( mg

3here% g ( acceleration due to gra"ity!

$%ample : The mass of a helicopter is /00 -". Hhat is the wei"ht of the helicopter

when it land on the pea- of a mountain where the "raitational field is

3.@? G -"51F ( mg

( 5-- 9


32/108

( *; 5; N


33/108



force% F

t G s

E%ercise 2.=

1. S-etch the followin" "raphs for an obIect that fallin" freely.

(a) isplacement5time "raph+

(b) Velocity5time "raph(c) 6cceleration5time "raph

&a' s G m &b' " G m s# &c' a G m s2

2. The followin" data was obtained from an e%periment to measure the acceleration due to

"raity.

Eass of steel bob 200 "+ distance coered !.0 m+ time of fall 0.@3 s.

,alculate the acceleration due to "raity of steel bob.Aie the e%planation why your answer different with the constant of "raitational

acceleration+ " 3.? m s52.

m t i( s i2n-a- s g tationary s ( sta$t !e- m t ( -!/< s u ( - g ( =

t i( s m

-!o2"i

k n g

g 3ith uniform "elocity

s ( ut . N >or g mt a

2

l reaction% Normal reaction% $!- ( - &-!/)he ans3er less

t ehia g

nht

t %h

e c

(om

ns g

tant because o3 f t

eh

ie gh

at i %r

fr (

icm

ti g

onal

force!

IDEA OF E>-I'I:RI-M FORCES Magnitude of ( Magnitude of ( mg cos θ

6n o bIeacntd is inaec#ts$iilni1or pi p$om siwtehd einre:ction! 0nd acts in opposite direction!

1. +o%…… …es…ult …an…t fo…rc…e (… … 1 … …(…-………+o… %…es…ult …an…t f …orc…e …( m… g …co… s …θ

& object in e6uilibrium ' & object in e6uilibrium

'

… 1 …(…

-……………

2. ………………………………………………………………………………………………

normal reaction%

friction force

eight%

Force % F ( Frictional force

t G s t G s


34/108



esultant force ( F 1 Frictional force( - &object 2in2 e6uilibrium'


35/108

2!

stationary obIect

6n obIect moin" with uniform elocity

Addition o! Forcea resultant force is a single force the

1. 6ddition of force is defined as ...……………………………………………………..represents in magnitude and direction t3o or more forces acting on an object ……………………………………………………………………………………………… F resultant ( the total of forces &including the directions of the forces'………………………………………………………………………………………………

L9amples : the forces are acting in one direction

;1 10 G

;2 G

=esultant force+ ; ( F . F 2 ( - . * ( * N

L9ample : the forces are acting in opposite directions

;1 10 G

;2 G

=esultant force+ ; ( F # F 2 ( - # * ( * N

L9ample : the forces are acting in different directions

;2 G


36/108

00 ;

Barallelo"ram method:

1. raw to scale.

2. raw the line parallel with ;1 to the ed"e of ;2+ and the line parallel with ;2 to the

ed"e of ;1

!. ,onnect the dia"onal of the parallelo"ram startin" from the initial point.

#. Eeasure the len"th of the dia"onal from the initial point as the alue of the

resultant force.

Trian"le method

+olution : esultant force% F ( 5--- 1 *$--1. raw to scale. (/-- N

2. isplace one of )h

thee y

f 3

oerc

rees

ntoo

ttihneee6

du"il

eib

or f iu

am

nother force.

!. ,omplete the trian"le and measure the resultant force from the initial

point.

$%ample 1: urin" Sport ay two teams in tu" of war competition pull with forces of

/000 G and !00 G respectiely. Hhat is the alue of the resultant forceF

6re the two team in equilibriumF

esultant force% F ( -!* 9 *-

( *2* N

;1 10 G

;2

;

;1


37/108

600

F

θ

F 9

re

$%ample 2: 6 boat in a rier is pulled horiJontally by two wor-men. Hor-men 6

pulls with a force of 200 G while wor-men while wor-men ' pulls with a

force of !00 G. The ropes use+ d ma-e an an"le 20 with each other.

raw aCos θ ( % therefore F 9 ( F cos θ

parallelo"ram and label the re+ sultant force usin" scale of 1 cm : 0 G.

etermine the ma"n+ iitnudθe(of +

y su %ltt ahnetrefo forcree. F ( F sin θ+

F 9 ( F cos θ ( *- cos 5-

( *- &-!*'

( 2* N

Resol$tion o! a !orce

Fy ( F +in θ ( *- sin 5--

F y ( *- &-!;55-'( 4$!$ N

re"erse process of finding the resultant force1. =esolution of a force is …………………………………………………………………

F y F is the resultant force of F9 and Fy )herefore% F can be resol"ed

into F9 F an(d m F g y sin 4-- . 2--( ;--&-!542/' . 2--

Dertical

Component

( *4!2 . 2--

( /4!2 N

hori8ontal component

mg ( ;-- N

=efer to tri"onometric formula:

$%ample : The fi"ure below shows 6li moppin" the floor with a force 0 Gat an an"le of /00 to the floor.

; 0 G

20

10. cm F 9


38/108



$%ample of resolution and combination of forcesF = ?

*ro1lem solvinthe resultant force is e6ual to 8ero!

1. Hhen a system is in equilibrium+ ……………………………………………………….

2. 7f all forces actin" at one point are resoled into horiJontal and erticalthe sum of each component is e6ual to 8ero!

components+ ……………………………………………………………………………

!. $%ample 19 Show on a fi"ure9

a) the direction of tension force+ T of strin" b) the resultant force act to lamp

700 700 c) calculate the ma"nitude of tension force+ Tma9imum 3hen both of forces act in same direction F a)T b) TK T &c ' )K ( 2) sin /-

-

F ma9imum ( ; . 5 ; N 24 N

( 24 N )herefore% mlamp g ( 2) sin/-- 5 N

F minimum 3hen thm

e l f aomprc

es1.

act

-"in

opposite direction

mlamp

& ) (

sin00

F minimum ( ; 1 5 Hlamp 1#.@ G

; N 2 N

E%ercise 2.?

( 2 N 5

N (

/.5.1 #

sin0

0

( /!;2 N

1. Two force with ma"nitude 1? G and / G act alon" a strai"ht line. Hith the aid ofdia"rams+ determine the ma%imun possible alue and the minimum possible alue of the

resultant force.

F ( esultant of Force

F 2 ( 22-2 . 2--2

F ( 2


39/108



2/


40/108



2. H=* is

1. Hor- is done+

2. 6 football is -ic-ed simultaneously by two players with force 220 G and 200 G

respectiely+ as shown in ;i"ure 2.3. ,alculate the ma"nitude of the resultant force.

200 G

-NDERSTANDIN) ;OR@3 ENER)( AND EFFICIENC(

;or hen a force that acts on an object mo"es the object through a……………………………………………………………………………..

distance in the direction of the force!………………………………………………………………………………………………

of a force and the distance tra"eled in the direction of product.…………………………………………………………………….

the force!………………………………………………………………………………………………

!. The formulae of wor-9 @O ( F@CL ,+PE0CLMLN) ( F % s

: 3ork in JouleGJ

F : force in Ne3tonGN

s : displacement in meterGm

#. $%ample 19

;orce+ ;

( Fs s

f% F ( 4- N and s ( 2

m 7ence% ( 4- 9 2

( ;- J

$%ample 29

2@

220 G

300


41/108



; /00 G

( F s

( 5-- 9 -!;( 4;- J

S 0.? m

) )

h

?0 G

/00

( Fs s m

( ;- cos 5-- &*'

( ;- &-!*' &*'

( 2-- J

$%ample !9

F ( $-

N ( !*

m ( F s ( F h

( $- &!*'

( 4*!- J

$%ample #9

Enery t is the potential to do 3ork!

1. $ner"y is .................................................................................................................created nor be destroyed!

potential energy% kinetic energy% electrical 2?

energy% sound energy% nuclear energy% heat and chemical energy!


42/108

23

2. $ner"y cannot be ....................................................................................................

!. $%ist in arious forms such as …………………...……………………………………

………………………………………………………………………………………………

#. $%ample of the ener"y transformation9

hen 3e are running up a staircase the 3ork done consists of energy change from………………………………………………………………………………………………Chemical Lnergy à Oinetic Lnergy à Potential Lnergy……………………………………………………………………………………………

…)he energy 6uantity consumed is e6ual to the 3ork done!

. ……………………………………………………………………………………………… f -- J of 3ork is done% it means -- J of energy is consumed!$%ample : …………………………………………………………………………………

……………

;or done and t"e c"ane in inetic enery

Force, F

s

energy of an object due to its motion!1. *inetic ener"y is …………………………………………………………………………

2. =efer to the fi"ure aboe+ork ( Fs

( mas

( m & > "2 '

)he formulae of Oinetic energy% Lk ( > m"2

!. $%ample 19 6 small car of mass 100 -" is moin" alon" a flat road.The resultant force on the car is 200 G.

a) Hhat is its -inetic ener"y of the car after moin" throu"h 10 mF

b) Hhat is its elocity after moin" throu"h 10 mF

+olution : ?i"en : m ( -- kg % F ( 2-- N

a! Oinetic energy% Lk ( Fs

( 2-- 9 -( 2--- J

b! Delocity% "à > m"2 ( 2---

" ( 5!$2 m s#

*hrou&h, v = u 2asu = 0

and, as = 3 v


43/108


m

!0


h 1.created or destroyed but can be changed from one form to

another form!energy of an object due to its position!

1. Araitational potential ener"y is………………………………………………………...&possessed by an object due to its position in a gra"itational field'

……………………………………… M …a9…im…um… P …ot …en…tia…l e…ne…rgy…………………………

…2. =efer to the fi"ure aboe9

Oinetic energy decrease ( Fs ( mg h 3here% F ( mg

+o% ?ra"itationa pl ot eennet r i g a yl %e L ne p r ( gymd g ehcrease

potential energy and kinetic energy!.

an

d $%ample9 7f m 10 -" ( - &-' !*

ncrease ( *-

J

increase

)herefore ork done ( *-J

*rinciple o! conservation o! enery 0nd% L p ( *- J Ma9imum kinetic energy

,arry out hands5on actiity 2.10 on pa"e !? of the practical boo-.

To show the p?riin"cein pl:eho(f c2o-nsme %ruat(ion- o % f g e(nethe rate of doing 3ork!

)herefore% po3er% P ( 3orkdon

e

timetaken

% so% P (

t

here% P : po3er in 3attG : 3ork in jouleGJ

t : time to do 3ork in secondsGs

!. $%ample in calculation : 6 coconut falls from a tree from a hei"ht of 20 m. Hhat is theelocity of coconut Iust before hittin" the earthF

;or done and ravitational potential enery


44/108



Devce!

mec"#e

*oer

1. Bower is …………………………………………………………………………………

2. 6 wei"htlifter lifts 1?0 -" of wei"hts from the floor to a hei"ht of 2 m aboe his head in

a time of 0.? s. Hhat is the power "enerated by the wei"htlifter durin" this timeF

" 3.? ms52) +olution : ?i"en : m ( ;- kg% h ( 2 m% t ( -!; s and g (

P ( (t

mght /10 × .1 × -

E!!iciency (0.1

( 4 4-

as the percentage of the energy input that is transformed into useful energy!1. efined……..…………………………………………………………………………….

2. ;ormulae of efficiency :

Lfficiency = se ful energy output

×100L Lnergy input

!. 6nalo"y of efficiency9un3anted energy

Lnergy input% L input Devce!

mec"#e

seful energy% L output

$ner"y transformation

+olution : ?i"en : m ( -!2 kg% s( -!4 m% t ( * s% L input ( -!; J

#. $%ample9(6a)n L eoluetpcutt r (ic=motor in a toy crane can lift a 0.12 -" wei"ht throu"h a

hei"ht of 0.# m in s. urin" this time+ the batteries supply 0.? & of ener"y to the motor. ,alculate

&a' The usefu L l oout f puot u(tp F ut 9o sf the motor.

&b' The efficiency of (th&-e!m2o 9tor -' 9 -!4

( -!4; J

&b' Lfficiency ( =

L =

output

Lfficiency L

input =

0.48

0.80


45/108


Chapter 2 : Force and Motion 9 100L

x 100% = /0L


46/108

,arry out hands5on actiity 2.11 on pa"e !3 of the practical boo- to measure the power.

E%ercise 2.&B

1. Hhat is the wor- done by a man when he pushes a bo% with a force of 30 G throu"h a

distance of 10 mF State the amount of ener"y transferred from the man to the force.

( F s )he energy transferred to the force ( (b) Hhat is his power if he completes this wor- in 20 sF

P (

t 2205

(250

( ;!;2


47/108

A**RECIATIN) T+E IM*ORTANCE OF MAIMISIN) T+E EFFICIENC( OF

DE8ICES

1. urin" the process of transformation the input ener"y to the useful output ener"y+……… some of energy transformed into un3anted forms of energy!

……………………………………………………………………………..

)he efficiency of energy con"erters is al3ays less than --Q!.……………………………………………………………………………………………..)he un3anted energy produced in the de"ice goes to 3aste!………………………………………………………………………………………………

$%ample of wastin" the ener"y9 Oinetic energy

………..…………………

7nput ene"y output

from the petrol ener"y

Lnergy loss due to Lnergy loss Lnergy loss Lnergy loss due to friction at

…………………… ……………. ……………… ……………………. friction in as heat as sound other parts in the..………………….. …………….. ………………….. …………………….

mo"ing parts engine..………………….. ……………. …………………. …………………….

#. The world we are liin" in face acute shorta"e of ener"y.

. 7t is ery important that a deice ma-es ……………………………………………the best possible use of the input energy!

……………………

;ays o! increasin t"e e!!iciency o! devices Lngine must be designed 3ith the capability to produce greater amount of

1. 4eat en"ines ……………………..………………………………………………………mechanical 3ork!………………………………………………………………………………………………

2. $lectrical deices. ...……………………………………………………………………... Light Fittings……………………………………………………………………………………………# replace filament light bulb 3ith fluorescent lamps 3hich ha"e higher efficiency!……………………………………………………………………………………………# use a lamp 3ith a reflector so that the illumination can be directed to specific areas……of the user!

……………………………………………………………………………………………… Air-conditioners.………………………………………………………………………………………………

# choose a model 3ith a high efficiency!………………………………………………………………………………………………# accommodate the po3er of air#conditioner and the si8e of the room………………………………………………………………………………………………# Lnsure that the room totally close so that the temperature in the room can be………………………………………………………………………………………………maintained!

………………………………………………………………………………………………

………………………………………………………………………………………………

2.

!.


48/108

1. $lasticity is

2. ;orces between atoms

Refrigerators………………………………………………………………………………………………# choose the capacity according to the si8e of the family!

………………………………………………………………………………………………# installed a3ay from source of heat and direct sunlight!

………………………………………………………………………………………………# the door must al3ays be shut tight!

………………………………………………………………………………………………

# more economical use a large capacity refrigerator!………………………………………………………………………………………………# use manual defrost consumption!

………………………………………………………………………………………………ashing !achines

………………………………………………………………………………………………# use a front loading as such more economical on 3ater and electricity

………………………………………………………………………………………………# front loading use less detergent as compared to a top loading machine!

………………………………………………………………………………………………

Operation o! electrical devices3hen they are in good operating

1. The electrical deices increase the efficiency………………………………….……condition!3ill increase the life span of de"ice!

2. Broper mana"ement ….....……………………………………………………………… L9ample : #the filter in an air#conditioner and fins of the cooling coil of a refrigerator

!. …………..………………………………………………………………………………must be periodically cleaned!

………………………………………………………………………………………………

-NDERSTANDIN) E'ASTICIT(

,arry out 4ands5on actiity 2.12 pa"e #0 of the practical boo-.the property of an object that enables it to return its original shape and

……………………………………………………………………………...dimensions after an applied e9ternal force is remo"ed!

………………………………………………………………………………………………)he property of elasticity is caused by the e9istence of forces of …………………………………………………………………..

repulsion and attraction bet3een molecules in the solid material!………………………………………………………………………………………………

!. ;orces between atoms in equilibrium condition

Force o$ re%'so#

Force o$ ())r(c)o#

Force o$ re%'so#

$%planation :

! )he atoms are separated by a distance called the e6uilibrium distance and "ibrate at ………………………………………………………………………………………………it position!

………………………………………………………………………………………………2! Force of repulsion ( Force of attraction

………………………………………………………………………………………………

#. ;orces between atoms in compression

compressie forcecompressie force


49/108



1. 4oo-eKs


50/108



QP

*

!

0 R + cm


51/108



k

F ( k9+pring obeying 7ookeKs Ea3 +pring not obeying 7ookeKs la3

&e9ceeded the elastic limit'

Force constant% k ( F 3ith unit N m# % N cm# or N mm# 9

5! Sprin" ,onstant+ -

;>G

0.?

0 ? %>cm

k is the gradient of the F # 9 graph

F (

90.1 1

( -! N cm#

$%ample 19 6 sprin" has an ori"inal len"th of 1 cm. Hith a load of mass 200 "

attached+ the len"th of the sprin" is e%tend to 20 cm.

a. ,alculate the sprin" constant. b. Hhat is the len"th of the sprin" when the load is in increased

by 10 "F Massume that g 10 G -"51N

?i"en : l o ( * cm% m ( 2-- g % F ( 2!- N% l ( 2- cm 9 ( * cma. k ( =% k ( x = 2.0 = 0.4Ncm 1

F −

5

b. l ( = % 3hen m ( *- g% F ( !* N From a% k ( -!4 N cm#

9 (+=

.5= ?.@cm

k 0.4

$%ample 29l ( * . ;!/* ( 2$!/* cm

The "raph shows the relationship between the

Araph ; a"ainst % of stretchin" force+ ; and the sprin" e%tension+ %.

F N

.

7

6/

sprin" B and sprin" C

P

Q

(a) ,alculate the sprin" constant of B and C.(b) 8sin" the "raph+ determine the

stretchin" force acts to sprin" B

and

sprin" C+ when their e%tension are 0. cm

+olution

a! +pring constant% k ( gradient of graph6 −k P (

40.3

8

=15.79N cm1

k B (2

3= 6.0 N cm

−

10.5

(


52/108


Chapter 2 : Force and Motion1

0 0.1 0.2 0.! 0.# 0.% (cm)

b! hen 9 ( -!*% F P ( ;!- N & e9trapolation of graph P'

F B ( $!- N


53/108

!@

%

Elastic potential enerythe energy stored in a spring 3hen it is e9tended or compressed

1. $lastic potential ener"y ………………………………………………………………..

sprin" with the ori"inal len"th

% sprin" compressed %

; % compression

% ; sprin" e%tended

; compression

% e%tension;+ e%tension

ther situation where the sprin" e%tended

and compressed

Relations"ip 1eteen or and elastic potential enery

F!N

F

Araph ; a"ainst %

+

0rea under the graph ( 3ork done

( > F9+o% Llastic potential energy ( > F9

$%ample 9

1/ cm

+ ! cm

/ g

. cm

9 ( * 1 ;

( / cm( -!-/ m

Force act to the spring%

F ( * 9 - ( *- N Llastic potential energy ( > F9

( > *- &-!-/' ( !/* J

Factors t"at e!!ect elasticity

4ands5on actiity 2.1! on pa"e #2 the practical boo- to inesti"ate the factors that affect

elasticity.


54/108

Type of material different same same same

iameter of sprin" wire same different same same

iameter of sprin" same same different same

$estions

1 Hhen a coconut is fallin" to the"round+ which of the followin"

quantities is constantF


55/108



Solution :

6. Velocity

'. Eomentum

#. Acce$eration

. *inetic ener"y

2 7n an inelastic collision+ which of thefollowin" quantities remainsconstant before and after the

collisionF

6. Total acceleration

Velocity > ms51

#

0 2 # / Time > s

,alculate the momentum of the

trolley from t 2s to t #s.

'. Total elocity

#. Tota$ !o!ent%!

. Total -inetic ener"y

,alculate the wei"ht of a stone withmass /0 " on the surface of the

moon.

6. 1. -" m s51

'. !.0 -" m s51

,. #.0 -" m s51

&. '.( )g ! s-

1

$. @. -" m s

51

P ( m"

( !* 9 4

( 5!- kg ms#

(The "raitational acceleration of the @. This fi"ure shows an aircraft flyin"moon is 1>/ that of the $arth.)

in the air. m"

2

&-!$'&-'&*' ( > &-!$' "2

" ( - m s#

P ( &-!$'&-'( $!- kg m s#

m 0.! -"

m


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Method &a'

)he forces gi"en parallel 3ith the surface of motion%

#2

3. 6 bi" ship will -eep moin" for somedistance when its en"ine is turned off.

10. 6n iron ball is dropped at a hei"ht of

10 m from the surface of the moon.

,alculate the time needed for theiron ball to land.

(Araitational acceleration of the

moon is 1>/ that of the $arth and" 3.? G -"52)

s ( ut . > gt 2

( &-'t . > &

ia"ram 1.1

ia"ram 1.1(i) and (ii) show two methods used by the mechanic to moe a brea-downcar. 6 constant force+ ; 00 G is used to push and pull the car in method 6 and '.

(a) (i) F H(hi F c g hi"emn #et F h f oricdtioins easier to moe the carF

…(…*-…- … 1 2…

--…………………………………………………………………

(ii) S(tat$e-a- r N eason for your answer in (a)(i).

……………………………………………………………………………… F ( F gi"en Cos *-

- 1 F friction

………………………………………………………………………………( *-- cos 5-- 1 2--

(b) The frictional force actin" between the car and trac- surface in both methods is

200 G. ,a(lc*u-la!-te N + the(i) horiJontal resultant force in method 6.

F ( m a

*-!- ( --- a(ii) horiJontal resultant force in method '.

a ( -!-* m s

)he acceleration of Car 0 ( -!$ m s#2

)o mo"e Car 3ith the same acce#l 0eration of Car 0% increase the force gi"en

This situation happens because the ship 6 0./ shas ' 1.# s

, 1.@ s

A. great inertia & . s

'. "reat acceleration $ 12.0 s,. "reat momentum

. "reat -inetic ener"y


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to --- N


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#1

(iii) acceleration of the car in method '.

( c ) Su""est a method to moe ,ar ' so that the acceleration produced is equal to thatof method 6.

……………………………………………………………………………..………..

………………………………………………………………………………………

2. ceilin"

Tin water E G hand

B C =

(i) ia"ram 2.1 (ii)

a) ia"ram 2.1(i) shows tin B that is empty and tin C that is filled with water. 6

student find difficult to pushed tin C. Hrite the inference about the obseration.)he difficulty to mo"e the tin depends to its mass!………………………………………………………………………………………

b) ia"ram 2.1(ii) shows a tin bein" released from the different positions E and G.

The hand of a student at position = needs "reater force to stop the motion of thetin fallin" from position E. $%plain this obseration.

From position M the "elocity of tin is more than the "elocity compare 3hen it is………………………………………………………………………………………

from N! L k increase then the force to stop it 3ill be increased!………………………………………………………………………………………

c) 'ased on the obseration (i) and (ii)+ state two factors that affect the ma"nitude of

the momentum of the obIect.

mass and "elocity………………………………………………………………………………………

d) 7f water flows out from a hole at the bottom of the tin C+ how would the inertia of Tin C depends on time F

inertia of tin B 3ill decrease because the mass of tin decreased!……………………………………………………………………………………

!. 2 ms51


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B iron ball ( 2 -" )

!.0 m smooth surfaceS T

1.0 m 2.0 m

C = ia"ram ! =ou"h surface

The fi"ure shows a iron ball that is rolled throu"h BC=ST. The rou"h surface of C= has

frictional force of # G.a) ,alculate

(i) the -inetic ener"y of the iron ball at B.

L k ( > m"2

( > &2'&22 ' ( 4!- J

(ii) the potential ener"y of the iron ball at B. L p ( mgh

( &2' &-' &$!-'

( 5-!- J

(iii) the total of ener"y of the iron ball at B. L ( L k . L p

( 4!- . 5-!-

b) ( 54!- J

c) (i) ,alculate the total of ener"y of the iron ball when it reaches at C F54!- J & the conser"ation of energy '

(ii) ,alculate the wor- done a"ainst friction alon" C=. ( F f 9 s

( 4 9 !-

( 4!- J

d) ,alculate the total -inetic ener"y of the iron ball at S. L s ( L 1 L f L k at + ( L s # L p at s

( 54!- 1 4!- ( 5-!- 1 &2'&-'&2!-'

( 5-!- J ( 2-!- J

e) ,alculate the speed of the ball at position T.

L k at ) ( 2-!- J "2 ( 2-

( > m "2 " ( 4!* m s#

( > &2'&"2 '

*art C / Essay >$estions

1.

#2


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#!

(i) (ii)

ia"ram 1.1

ia"ram 1.1(i) shows the condition of a car moin" at hi"h elocity when it suddenly

crashes into a wall.ia"ram 1.1(ii) shows a tennis ball hit with racquet by a player.

a) (i) Hhat is the meanin" of momentumF

(ii) 'ased on the obserations of ia"ram (i) and (ii)+ compare the

characteristics of car when it crashes into the wall and the tennis ball when

it is hit with a racquet. 4ence+ relate these characteristics to clarify a

physics concept+ and name this concept. b) $%plain why a tennis player uses a taut racquet when playin".

c) 7n launchin" a roc-et+ a few technical problems hae to be oercome before theroc-et can moe upri"ht to the s-y. 'y usin" appropriate physics concepts+

describe the desi"n of a roc-et and the launch techniques that can launch the

roc-et upri"ht.

0ns3e

r a' &i' momentum is product of mass and "elocity

&ii' # )he shape of car changed but the shape of 3all remained!# )he shape of ball remained but the shape of the rac6uet string 3as

changed! &)he rac6uet string is elastic but the 3all is harder'# )he time taken of collision bet3een the ball and rac6uet string

more than

the time taken 3hen the car hit the 3all!# )he impulsi"e force 3ill decrease 3hen the time of collision increased!

# )he concept is the impulsi"e force!

b' # )o decrease the time of collision bet3een the ball and the rac6uet string!

# mpulsi"e force 3ill be increased!

# )he force act to the ball 3ill be increased!# )he "elocity of ball 3ill be increased!

c' # Make a gradually narro3er at the front shape &tapering'

: )o decrease air friction# Made by the high strength and high rigidity of materials

: )o decrease the probability to become dented &kemik'!

# Made by the lo3 density of material!


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: )o reduce the massG3eight

# )he structure is fractional engine

: )he mass 3ill be decreased and the "elocity 3ill increase!# Made by the high of heat capacity of materials

: t 3ill be high heat resistance!

2.Broperties

'rand =eaction time > s Eass > -"$n"ine thrust

force > G=esistance force

> G

6 0.! 1. 10.0 #.0

' 0. 1.? 12. 2.#

, 0.2 0.3 /. 2.2

0./ 2. 1/.0 /.

7n a radio5controlled car racin" competition+ # mini5cars branded 6+ '+ , and too- part.

The information of the # cars is "ien in the table aboe. etails of the aboe information

are "ien as below9

=eaction time 5 uration between the moment the radio5controlled is switched on and

the moment the car starts moin".=esistance 5 6era"e alue of opposin" forces includes the friction between

wheels and trac-+ and air resistance.

(a) Hhat is the meanin" of accelerationF

(b) raw a "raph of elocity a"ainst time that shows a car moin" initially with

constant acceleration+ then moin" with constant elocity and followed byconstant deceleration until it stops.

(c) $%plain the suitability of the properties in the aboe table in constructin" a radio5

controlled car racin" purpose. 4ence+ determine which brand of car will win the05metre race.

(c) 7f ,ar ' in the aboe table is moed up the plane at the an"le of !0o to thehoriJon+

(i) Show that the car is able to moe up the plane.

(ii) etermine the acceleration of the car. 0ns3er :


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&a' ncrease the "elocity

&b' " G ms#

displacement ( area under the graph

t G s

&c' # time reaction mast be short : fast to detect the signal to start its mo"e# has a small of mass : to decrease the inertia% then easier to start mo"e and

to stop its mo"ing!

# thrust force is high : has more po3er during its mo"ing G increase the

acceleration# friction force is lo3 : decrease the lost of force

# the best car is 0 : because it has short of time reaction% small of mass% high of

thrust force and lo3 friction of force!&d' &i' L ( &2!* 1 2!4 ' &*-' ( *-*!- J

*- m *-+in$-- L &suitable to mo"e up' ( !;

&-'

&*-+in$-

-

'

!00

( 4*- !- J L L & car can mo"e up the plane'

&ii' F ( ma % 2!* 1 2!4 ( !; a% a ( *!5 ms#


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!/

chapter 2 force and motion (answer)

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