section 1 specification edexcel

8/10/2019 Section 1 specification edexcel

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Section 1: Forces and Motion

You will learn following topics in this section

a) Units

b) Movement and position

c) Forces, movement, shape and momentum

d) Astronomy

a) Units

On this and next two pages you will learn Physical quantities, their definitions and units.

Students must learn units by heart

S.No Quantity with DefinitionSymbol used for

quantityunit

S

l

fo

4

a) Units

On this and next two pages you will learn Physical quantities,

their definitions and units.

Students must learn units by heart

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VELOCITY

Definition:Rate of change of distance per unit time in a particular direction.

OR

Rate of change of displacement.

For exams write word equation for definition as given below

Note#1:There is fundamentally no difference between speed and velocity

except that velocity has direction.

Velocity = speed + direction.

Note#2:It is a vector quantity.

How speed is different from velocity?

only in direction!

A car driving along a highway from one town to another, its speed might be

constant, but the velocity changes as it will change several directions during

the course; as shown in the following figure

v Meter/second


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The speed is same on all three points while direction is being changed

therefore velocity changes.

If youre moving along at 25 m/s and then you come to a bend in the road,your

velocity changes because your direction changes.

5

ACCELERATION

Def ini t ion: Rate of change o f veloci ty per unit t ime.

But do not w ri te this def in i t ion in exam if asked.

Note#0: Just wri te the fol lowing form ula dur ing exams if def in i t ion is

asked.

sym bol ical ly , above form ula can be wri t ten as

where, "a" s tands for accelerat ion.

"v" for f inal veloci ty .

"u" for ini t ia l veloci ty .

" t " for t ime.

Note#1: It 's a vecto r quanti ty.

a Meter/second2 m

6

FORCE

Definit io n: It is anAGENT which can change the shape, direct ion and

speed of an o bject .

Note#1: I f force's def in i t ion is asked in exam then w ri te the fol lowing

formula.

Force = Mass x Accelerat ion.

symbol ical ly ,

F = m x a

F Newton
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7TIME

Def ini t ion: beyond the scope of IGCSE.

t

Always use

"second"

but "minutes",

"hour" or even

"days", "months"

Or "years" may

also be used if

specified or asked

in question

8

GRAVITATIONAL FIELD STRENGTH

OR

Accelerat ion due to Gravi ty

Def in i t ion: The amount o f gravi tat ional force pul l ing anOBJECT of

mass 1 ki logram towards the center of earth or any celest ialOBJECT .

Note: Celest ia l object means any astronom ical object l ike moo n, mars

etc.

Explanat ion: The Earth is surround ed by an invis ible gravi tat ional f ield.

This f ie ld exerts a force (cal led w eight)

on al l m asses which are placed in the f ie ld.

On the su rface of Earth, this st rength of force is 10 N on every 1 kg. This

st rength is calculated by

gravi tat ional fie ld st rength =Weight /mass; (w upon m)

Since this s t renght is a rat io, therefore, i t is a c onstant qu ant i ty .

On Earth, gravitat ion al f ield strength , g = 10 N/kg.

I t is a vector quant i ty .

Note:

The symbo l "g" is also used for the term "accelerat ion due to gravi ty" .

Accelerat ion due to gravi ty is the amoun t of accelerat ion produ ced due

to the gravi tat ional pul l .

There is no conceptual di f ference except ; when "g" is used as

accelerat ion du e to gravi ty i ts un it is m/s2

However, when it is us ed as gravi tat ional f ield st rength its unit w i l l be

N/kg.

g

symbolic definition is

g=w/m

Note: The symbol 'g'

is used for two terms

'acceleration due to

gravity' &

'gravitational field

strength.

However, there is no

fundamental

difference between

both of them

Gravitational field

strength is

measure

in Newton/

Kilogram

While

Acceleration due

to gravity is

measured in

meter/ second2

N

m

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MOMENTUM

Def ini t ion: Quant i ty of mot ion in a body.

But i f Def in i t ion is asked in exam it would be the fol lowing formu la

Momentum = mass x veloci ty .

Note#1: It 's a vecto r quanti ty.

PKilogram.meter/

seconds

(k
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1.2 EXAMINER'S EXPECTATION: PLOT AND INTERPRET DISTANCE-TIME

GRAPHS

Edexcel people love graphs and distance-time graph is no exception. You people need to know all which I have

written down for you. All that is written is only for the sole purpose of making you eligible for A-gradenot to

make you expert on this section of graphs. Everything is possible in love and war-- obviously, examination can

not be your love.

Therefore,

Let's begin! Three types of questions are usually asked

i) Describe a graph

ii) Plot a graph for a given situationiii) WORK out quantities from graphs

I- DESCRIBE A GRAPH:

Step 1:Baby stuff

In distance-time graph: distance always comes on Y-axis and time on X-axis. You will encounter different

shapes of graphs and every shape has different meaning.

Step 2:Learn some shapes

Before we start our discussion on examiners' maneuvers you need to learn that people who make papers have

only few types of graphs in their box, which are dished out in one way or other to you during examination's

papers. However, if you learn them all you can grab full marks.

A very important note:

The absolute essential commandment which your father and mother will probably never tell you; even Moses

had never told anyone is that

"gradient/steepness is the most important thing in graphs."
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Whenever you are asked to analyze graphs, you should become a narrow minded person i.e. always think about

its gradient-- this will probably change your marks forever.

So for distance-time graph keep your focus on gradient of the graph.

Look at the graphs on following pages and let's face them one by one.

Graph-A:

Description of Graph A:

Gradient or steepness of distance-time graph shows "speed of the object". And a straight diagonal line on distance-time

graph shows constant speed or average speed. Higher the gradient higher the speed as shown below.

In above diagram lines a,b & c represent different gradients/steepness. Line "a" is the steepest therefore has higher

average speed than the rest where as "c" has the lowest average speed.

GRAPH B:


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Description of Graph B:

In this graph gradient or steepness is zero as line is horizontal.

A straight horizontal line on distance-time graph shows that object is at rest/stationary.

Explanation:

In this graph distance is not increasing as time is increasing. This is only possible when object is not changing its

position or is at rest.Note:Examiners may give you a situation and ask you to draw the graph of the situation orExaminer may exhibit a

graph and ask you to describe it, Similar to the one given on next page.

But remember!"gradient/steepness is the most important thing in graphs." Whenever you'r asked to analyze a graph

just go for the gradient it's the key.

GRAPH C:

Description of Graph C:

This is a curve graph. A curve line on distance-time graph shows that object is either accelerating or decelerating.

A curve line which is getting steeper and steeper with time on a distance-time graph represents acceleration.Explanation:

Above graph shows that distance is increasing as time is increasing. Also notice that as time is increasing the graph

is getting steeper and steeper.

If a graph is getting steeper at faster rate it means its acceleration is higher as shown in following graphs

Above graph shows three curves, representing three objects, all of them are accelerating. All of them have covered a

same distance of 50 meters but in different times. Curve


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"a" has covered the distance much earlier than curve "b" & "c" which means curve "a" has highest acceleration in all

Conclusion:

Lines which get more vertical over time on a distance-time graph are called "acceleration graphs".

GRAPH-D:

Description of Graph D:

Remember the most esoteric commandment about gradient.

We know that Steepness represents speed on distance-time graph. If steepness increases then speed increases And if

steepness decreases then speed decreases.

The graph shown above is getting less steep over the time. Therefore, speed is decreasing which means object is

decelerating.

Conclusion:

Curve graphs which gets more flat over the time are "deceleration graphs"

GRAPH-E:

Description of Graph E:

This graph requires some knowledge of mechanicspart of Physics.

Gravity of Earth pulls every object towards itself (ground). When an objects falls, the constant pull of gravity

accelerates the object thus speed of falling object increases unit they hit the ground.


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When you throw something up, it goes against the gravity so gravity decelerates it and thus speed decreases

constantly until it reaches the highest point.

Therefore, the gradient of the graph keeps falling--that's why thegraph of an object going freely against the gravity is

deceleration graph.

GRAPH-F:

Description of Graph F:

Gravity of Earth pulls every object towards itself (ground). When an objects falls, the constant pull of gravity

accelerates the object thus speed of falling object increases unit they hit the ground.

Therefore, the graph of a falling object is acceleration graph.

Note#1: In examination you would be given straight line graphs. Curve graphs are very rare and for descriptive

purpose.

Note#2:Examiner can only ask you to find speed on distance-time graphs. This can be done by finding the

gradient.

A note on finding gradient/slope of straight line:

Gradient/slope is the defined as how steep is the line. It is represented by small 'm'.

Mathematical formula:

m = rise (how high the line is going on Y-axis) / run (how far it's going on X-axis)

John left his home and walked 3 blocks to his school, as shown in the accompanying graph.


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What is one possible interpretation of the section of the graph from point B to point C?

(1) John arrived at school and stayed throughout the day.

(2) John waited before crossing a busy street.

(3) John returned home to get his mathematics homework.

(4) John reached the top of a hill and began walking on level ground.

Answer: (2) John waited before crossing a busy street.

II- DRAW OR PLOT A GRAPH FOR A GIVEN SITUATION

Always put "distance" on Y-axis and "time" on X-axis unless told otherwise. Always put units along with quantities

in brackets. As shown in graph below; distance (m) and time

(s). For plotting graphs two

types of questions are possible

Type 1:Examiners may give you a situation and ask you to draw its graph OR examiner may exhibit a graph and

ask you to describe it similar to the one given below.

Example

(a) A student walksFROM HOME to a library, waits to collect a book and then runs to a

friend's house.

The distance-time graph for the student is shown. Three sections of the graph are

labelled P, Q and R.

Complete the sentences with P, Q or R.
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(i) The student is walking at constant speed in section ........................................ .....(1)

(ii) The student is waiting at the library in section ...............................................(1)

(iii) The two sections of the graph that take equal amounts of time are

.............................. and ..............................(1)

(b) Use words from the box to complete the sentences.

You may use each word once, more than once or not at all.

(i) My answer to (a)(i) is because the section of the graph is

........................................ and ..................................................... (2)

(ii) My answer to (a)(ii) is because the section of the graph is

.....................................................................................................(1)

(c) How does the graph show that the student's friend lives nearer to the library than the student does?

.....................................................................................................(1)

(Total 7 marks)

Answersa-(i)P ; a-(ii)Q ; a-(iii) Q and Rb-(i)Sloping straight; b-(ii) Horizontal c-Less distance travelled in section

R than in section P

Type 2: Examiners may also give you a table in which values for distance and time is given and may ask you to plot

graph of the situation. Try following example.

Example

The table gives information about a journey made by a cyclist.

(a) Plot these points on the grid given below. (3)


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(b) (i) Use your graph to find the distance in kilometres which the cyclist travelled in 4.5 hours.

Distance = ..........................km (1)

(ii) Use your graph to find the time in hours taken by the cyclist to travel 35 kilometres.

Time = ............................ hours (1)

(c) State the equation which relates average speed, distance moved and time taken.

................................................................ (1)

(Total 6 Marks )

Example#2 Answers

a- all points correct

b(i)-Answer in the range of 67 to 68 (this will be different for you if you are printing it)

b(ii)- 2.3 to 2.4 (again this will vary)


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c- average speed = (distance moved) / time taken

Note#1: Mostly straigth lines' questions will be asked. However, very simple questions relating to accelerating and

decelerating may be asked in which examiner may be asking how far object has travelled in particular time.

III-WORK OUT OF QUANTITIES FROM A GRAPH

From distance-time graph, the quantities that you can find out are

i- The Average Speed of the object which can be found by finding the gradient of the graph.

ii- Distance travelled by the object in a particular time.

Alice runs a race the motion of which is plotted on a distance-time graph as shown below.

i- Over what distance ws the race run?

ii- How long did the runner take to cover this distance?

iii- How can we conclude from the graph that the runner ran at a steady speed during the race?

iv- what was the runner's average speed?

v- On the same axes plot a graph for a runner who ran 96 m in 12 seconds at a steady speed.

vi- Calculate the speed at which this runner ran the race.

i- 68 m ii- 8 sec iii- constant gradient iv- 8.5 m/s v- Just draw a straight line from zero to 96 m upto 12 seconds.

vi- 8 m/s

1.3 EXAMINER'S EXPECTATION: STUDENTS SHOULD BE ABLE TO KNOW AND

USE THE RELATIONSHIP BETWEEN AVERAGE SPEED, DISTANCE MOVED AND

TIME:

average speed =

Calculate the speed of an object which has covered a distance of 5 km in 2 minutes.


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Important note: standard unit of distance is not kilometer but meter and standard unit of time is not minutes but

seconds. In exams, we must keep our units in standard form unless told otherwise.

Solution:

Distance = 5 km = 5000 m and Time = 5 minutes = 5 x 60 = 120 seconds

Using above formula and pluging values

Avg. speed = 5000 / (2 x 60) = 41.67 m/s

1.4 EXAMINER'S EXPECTATION: STUDENTS SHOULD BE ABLE TO DESCRIBEEXPERIMENTS TO INVESTIGATE THE MOTION OF EVERYDAY OBJECTS SUCH

AS TOY CARS OR TENNIS BALLS

When a question about investigating motion is asked, then they would either ask you to experiment to find out

either i- Average Speed OR ii- Acceleration

TO FIND OUT AVERAGE SPEED OF TOY CAR OR TROLLEY:

Since we know that Speed = Distance / time. Therefore, to find out speed experimentally we must need have known

Distance & Time.

APPARATUS: Toy car or Tennis ball , meter rule , pully , slotted masses , stop watch, thread.FIGURE:

Procedure:

i- Put Toy Car on bench and attach pully to the corner of the bench as shown in figure.

ii- Attach one end of the thread with toy car and other end with slotted masses while hanging them over pully.

iii- Keep toy car & pully one meterAPART with meter rule.

iv- Hold the toy with hand so that it remains there immovable.

vi- Time stop watch when you let toy to move a meter distance.

vii- Repeat this & record readings for different distances in the following chart.
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viii- Draw graph to find out average speed, which can be found by finding gradient of graph.

PRECAUTIONS:

i- Do not hang heavier masses this may broke the thread.

ii- Wear shoes so as to avoid injury to foot in case of thread broken and masses fall.

iii- Put something soft underneath hanging masses like tray filled with sand.

SOURCES OF ERROR:

i- Reaction time.

ii- Ruler may not be straight.

iii- Parallax error.

iv- Friction in the bench.

Improvements In Trolley Experiment to avoid/reduce errors

i- Bench should be very polished friction.

ii- Tyres of the toy should not be very rough.

iii- Use light-gates instead of the stop watch and connect light-gates to datalogger and then to computer as shown in

followign diagram.

Animation: calculating speed using one light gates


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Animation: calculating speed using two light gates

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Note: You may use trolley/toy car instead of tennis ball in this experiment.

APPARATUS: Toy car or Tennis ball , meter rule , pully , stop watch.

Diagram:

PROCEDURE:

i- Put meter rule on one side of the bench.

ii- Give gentle push to the ball & switch on stop-watch.

iii- Stop stop-watch when ball covers a distance of 1 meters.

iv- Repeat this & record readings for different distances in the following chart.

vi- Draw graph to find out average speed, which can be found by finding gradient of graph.

SOURCES OF ERORR:

i- Reaction time.

ii- Parallax error

MEASUREMENT OF ACCELERATION

APPARATUS : Ticker timer and tape, a.c. power supply, trolley, runway

DIAGRAM
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PROCEDURE

1. Set up the apparatus as in the diagram.

2. Connect the ticker timer to a suitable low-voltage power supply.

3. Allow the trolley to roll down the runway.

4. The trolley is accelerating as the distance between the spots is increasing.

5. The time interval between two adjacent dots is 0.02 s, assuming the ticker timer marks fifty dots per second.

6. Mark out five adjacent spaces near the beginning of the tape. Measure the length s1.

7. The time t1 is 5 0.02 = 0.1 s.

8. We can assume that the trolley was travelling at constant velocity for a small time interval.

Thus initial velocity u = distance/time = s1/t1

9. Similarly mark out five adjacent spaces near the end of the tape and find the final velocity v.

10. Measure the distance s in metres from the centre point of u to the centre point of v.

11. The acceleration is found using the formula: v2= u2+ 2as or a = v2u2/ 2s

12. By changing the tilt of the runway different values of acceleration are obtained. Repeat a number of times.

13. Tabulate results as shown.RESULTS

CONCLUSION

We set out to measure acceleration and at the end of the day thats exactly what we did. We conclude with the ardent

wish that not all experiments are this mind-numbingly boring.

NOTES

1. Ignore the initial five or six dots on the tape since the trolley may not be moving with constant acceleration

during this time interval.

2. Ticker timers that use pre-carbonated tape are recommended because the friction due to paper drag is reduced.

3. Ensure that the voltage rating of the timer is not exceeded.

4. Some timers make one hundred dots in one second.

MEASUREMENT OF ACCELERATION DUE TO GRAVITY (g) USING THE FREEFALL METHOD

APPARATUS : Millisecond timer, metal ball, trapdoor and electromagnet.


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DIAGRAM

PROCEDURE

1. Set up the apparatus as shown. The millisecond timer starts when the ball is released and stops when the ball

hits the trapdoor.

2. Measure the distance s using a metre stick.

3. Flick the switch to release the ball and record the time t from the millisecond timer.

4. Repeat for different values of s.

5. Calculate the values for g using the equation s = (g/2) t2. Obtain an average value for g.

6. Draw a graph of s against t2and use the slope to find a value for g (g will be twice the slope).

RESULTS

CONCLUSION

When we plotted the graph, the slope worked out to be 4.85, which resulted in a value for g of 9.9 m s -2, which is

pretty damn close to the theoretical value of 9.8 m s-2. Conclusion? We rock!

PRECAUTIONS / SOURCES OF ERROR

1. For each height s repeat three times and take the smallest time as the correct value for t.

2. Place a piece of paper between the ball bearing and the electromagnet to ensure a quick release.

3. Remember to convert from milliseconds to seconds.

NOTE

Both points 1 and 2 above are associated with the problem that even though you switch off the power for the

electromagnet (and in so doing switch on the timer) it will not lose its magnetism immediately, therefore the ball

will not fall straight away. This means that the reading on the timer will always be (slightly) longer than the time for

which the ball was dropping.

Finding Acceleration using light gate


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Finding Acceleration with one light gate

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Finding Acceleration with two light gates

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1.5 EXAMINER'S EXPECTATION: STUDENTS SHOULD BE ABLE TO RECALL AND

USE THE RELATIONSHIP BETWEEN ACCELERATION, VELOCITY AND TIME:

acceleration =

a =

acceleration's definition is already given in table of section 1.1.

Acceleration is produced when speed of an object increases. And when the speed of the object decreases then it is

called deceleration or retardation. It's the opposite of acceleration or -ve acceleration.

For example, by pressing the accelerator of the car speed increases. And by pressing the brakes speed decreases we

call it deceleration.

Deceleration is calculated with the same forumual as that of acceleration. However, we put negative sign with the

acceleration to show it as a different number. As if acceleration = 5 m/s2then deceleration would be acceleration = -

5 m/s2

Caution:

Examiner would always try to confuse you with signs.

Note: If you are calculating deceleration then you may write it as deceleration = 5 m/s2or acceleration = - 5 5

m/s2but not as deceleration= - 5 m/s2as -ve of deceleration is acceleration.

Suppose you are solving a question to find acceleration. Your answer is coming as a negative number. And we

know that -ve acceleration is called deceleration. Then how should you write your answer ?

either

a) Acceleration = - 5 m/s2 or b) Deceleration = -5 m/s2 or c) Deceleration = 5 m/s2

The correct answer is either (a) or (c ) and if you are thinking for (b) then you will lose marks for your entire answer

in exam paper.

This is becauseve acceleration automatically means deceleration. And if placingve sign after deceleration would

change its meaning to acceleration as

-ve acceleration = deceleration AND

ve deceleration = acceleration.

Note:Two types of questions will be asked

Type 1:problems in which initial speed, final speed and time will be given. You just have to use formula to find

acceleration. These are dead easy, just apply formula and then plug and play.

Type 2:find acceleration by using graphs. Only speed-time or velocity-time graphs will be given. Because

remember the gradient. This topic is covered in section 1.6
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1.6 Examiner's Expectation: Students should be able to plot and interpret velocity-time

graphs

Similar to the distance-time graph, three types of questions are asked in velocity-time graph

i) Describe a graph

ii) Plot a graph for a given situation

iii) Work out quantities from graphs

I-DESCRIBE A GRAPH:

Always put velocity on Y-axis and time on X-axis unless told otherwise. Always put units with velocity and time on

their respective axes in brackets as shown in graph below

To describe a graph you need to know few shapes first before entering into the den of examiner.

The graph shown above has zero acceleration,this can be proved in two ways.

1-Gradient represents accelerationon on velocity-time graph. The graph is a straight horizontal line i.e. gradient is

zero. Therefore,acceleration is zero.2- A Straight horizontal line represents constant velocity on velocity-time graph. Since, acceleration means

increasing velocity not constant velocity,therefore, the graph has zero acceleration.

A straight diagonal line which is going upwards on velocity-time graph represents constant accelration.

A straight diagonal line going downwards represents constant deceleration. Gradient would come -ve gradient.

note: A curve line represents incr easing or decreasing acceleration. I f curve is going up i ts increasing

acceleration, i f it is going down f rom i ts deceleration and

i f the graph is flattening out i ts decreasing speed

Explanation of Constant deceleration graph:

First, notice that as time is increasing velocity is decreasing this concludes that it is deceleration graph--since

decreasing speed or velocity is called deceleration.

Second, it is straight diagonal line going downwards. A straight diagonal line represents constant gradient but if the

line is going downwards its -ve gradient. So a -ve gradient on velocity-time graph represents deceleration.

Explanation of increasing acceleration graph:

First, notice that graph is going up which means it is acceleration graph. Second, the graph is not straight line but its

steepness is increasing, therefore, it concludes that it is increasing acceleration.

Explanation of decreasing acceleration graph:


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The steepness is gradually decreasing which means that rate of increase of velocity is falling. Therefore, we can

conclude that object is accelerating at slower rate.

Above two graphs are curves going downwards as time is increasing, which means velocity is decreasing. So above

graphs are deceleration graphs.

In increasing deceleration graph, the graph is getting steeper and steeper negatively/downwards as time increases this

means deceleration is increasing. Reminder: deceleration is related tonegative gradient or steepness.

In decreasing deceleration graph, the graph is getting less steep as time increases but still falling down. This means

object is decelerating but slowly.

II- PLOT A GRAPH FOR A GIVEN SITUATION

A situation will be given to you during examination, and you will be asked to plot its graph.

For plotting graphs, two types of questions are mainly asked

Type 1:A situation is described and a question is asked to draw the graph of this situation.

see part b(ii) of example given at the end of the page.Type 2:A table is given in which values for velocity and time are present and a question is asked about graph.

III- WORK OUT QUANTITIES FROM GRAPH:

Always put velocity on Y-axis and time on X-axis unless told otherwise. Always put units with velocity and time on

their respective axes in brackets as shown in graph below.

Velocity-time graph is more diverse than distance-time graph. It can provide more information as you can find two quantities from it:

1stis distance and 2ndis acceleration.

To work out distance you have to find total area under the graph. Since in a velocity-time graph area under graph represents distance

travelled.

To work out acceleration you have to find gradient of the graph. Since in a velocity-time graph gradient represents acceleration.

Note: "work-out" questions will deal only straight-line graphs.

Practice Question:

o A model train travels between two stations. The velocitytime graph shows the train's motion.
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(a) (i) State in which part of the journey A, B or C the train is decelerating.

.......................... (1)

(ii) Explain your answer.

..................................................................................................................(1)

(iii) What does the graph show about the deceleration?

..................................................................................................................(1)

(b) (i) What feature of the graph represents the distance travelled between the two

stations?

..................................................................................................................(1)

(ii) A second train travels between the two stations at a constant velocity. It takes the

same time as the first train. On the axes above, draw a line showing the motion

of the second train. (3)

..................................................................................................................

(Total 7 marks)

Answer

o (a) (i) C (ii) -ve gradient (iii) constant deceleration

(b) (i) Area under the graph (ii) constant speed means straight horizontal line cutting approximatley the center of A

through C, ending at the same time.
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section 1 specification edexcel

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