Midterm 1 review

• How you will be seated• What you need to bring• Preparation of formula sheet• Exam Strategy

R i• Review

PHY 2311

Exam

• Prepare formula sheet: one 8.5x11 sheet – both sides if needed

• Bring sheet , pens or pencils, and a calculator to this room during the normal lecture time. Also bring your student ID.bring your student ID.

• You will be seated in a specific row. A seating chart will be displayed on the screen.

• You will be given a personalized exam with attached scratch paper.

• We will collect exam bubble sheet and scratch• We will collect exam, bubble sheet, and scratch paper when you hand in the exam. We will also check your ID.

• We will insist on the time limit. Please do not force us to take the exam from you.

formula sheet

• Hopefully you have prepared a formula sheet and used it to solve review problems.

• If you have not, you can select formulae from the first pages of each of my lectures and add formulae or notes if you find it useful for solvingformulae or notes if you find it useful for solving problems.

• At the beginning of each lecture, I collect some of the relevant formulae needed to solvesome of the relevant formulae needed to solve the problems. In the next pages, I have collected many of these formulae. If you don’t l d h f l h h

• Main points of today’s lecture

already have a formula sheet, these can serve as a beginning.

• Main points of today s lecture

0xv ; t t tt

x v t

Δ= Δ = −Δ

Δ = Δ0

0

for constant acceleration: a a; assuming also t 0v v at

= == +

t 0xv limt

va ; v a t

Δ →Δ=Δ

Δ= Δ = Δ

( )o

2

1x v v t2

1x v t at

Δ = +

Δ = +

t 0

a ; v a tt

va limtΔ →

= Δ = ΔΔ

Δ=Δ

0

2 20

x v t at2

v v 2a x

Δ = +

− = Δ

S i ts f ti l M i i ts f t d ’s l t• Some points of vertical motion:

gtvv −== downwards m/s 9.8 g

0

2

• Main points of today’s lecture:• Example: addition of velocities• Trajectories of objects in 2

dimensions:

( )tvvyyy

gtvv

o

Δ

+=−≡Δ

121

2

0

0 dimensions:

2 downwards m/s 9.8 g =

ygvv

gttvy

Δ−=−

−=Δ

22

20

2

20

( )tvvyyy

gtvv

yoy

yy

0

0

21 +=−≡Δ

−=

• Here we assumed t0=0 and the y axis to be vertical.

• Vectors and components ofygvv

gttvy

y

y

y2

02

20

221

Δ−=−

−=Δ

• Vectors and components of vectors

• Addition and subtraction of vectors

tvxvv

x

xx

0

0

=Δ=

• Main points of today’s lecture:Main points of today s lecture • Newton’s 1st law:

• If there is no net force, the velocity of a mass remains constant (neither the magnitude nor the ( gdirection of the velocity changes).

• Newton’s 2nd law:• m is the mass of the object. It is proportional to

amF =

j p pthe number of nucleons (neutrons and protons) in an object.

• is the net (total) force acting on the object. It is the vector sum of all forces acting on the

F

It is the vector sum of all forces acting on the object.

M i i t f t d ’ l t• Main points of today’s lecture:• Normal force• Newton’s 3d Law• Frictional forces:

– kinetic friction: – static friction

Nf kk μ=Nf μ<static friction

• Examples.Nf ss μ<

M i i t f t d ’ l t• Main points of today’s lecture:• Work:

( ) xFsFW xΔ=Δ= θcosF

• Kinetic energy:2

21 mvKE =

θsΔ

F

• Work-energy theorem:

P t ti l f it

2

0KEKEW ftotal −=• Potential energy for gravity:

• Conservation of energy ( )00 yymgPEPEPE ff −=−=Δ

00 PEKEPEKEE ff +=+=

• Main points of today’s lecture:• Cons. of Energy with Gravity• Potential energy of spring 1Potential energy of spring

W rk n r nd n n c ns rv tiv nd xt rn l f rc s

2

21 kxPE =

• Work, energy and non-conservative and external forces

f 0 f 0 mech,f mech,0KE KE PE PE E EW W

− + − = −

• Powernonconservative extW W= +

Wave ave ave

WP ; P Fvt

= =Δ

Problem solving strategy• Look through the exam and do the easiest problems first.• On each problem, you can use the following “fool proof”

procedure to solve the problem:procedure to solve the problem:• Read the problem carefully.• If necessary, draw a picture.

Id if h h i i i l h i l d i h• Identify the physics principles that are involved in the problem.

• Identify the known values given in the problem and k l fi dunknowns values you are expect to find.

• Choose the appropriate equations that can be used to get the unknown you are suppose to find.

• Count the number of equations and verify that the number of equations is at least equal to the number of unknown quantities that are in the equations.

• Solve.

Review

• I have selected 14 problems that illustrate the principles that are involved for problem sets 1-4.

• If I finish these problems, I will accept requests for additional problems as time allows.

• An answer key will be posted on the Physics 231• An answer key will be posted on the Physics 231 web site after the lecture for section 3

What is the displacement at t=4 s.

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