Name: _______________________________________________

CS P1 F Forces and motion

Date:

Time: 39 minutes

Total marks available: 39

Total marks achieved: ______

Questions Q1.

Shot-put is an Olympic event. The shot is a heavy ball. An athlete throws the shot as far as possible.

A sports scientist analyses an athlete's throw to help improve performance.

The scientist can measure several quantities in the analysis.

Which one of the following is a scalar quantity?

(1)

A acceleration

B force

C mass

D velocity

(Total for question = 1 mark)

Q2.

The distance-time graph for a car is shown below.

Describe what the graph shows about the speed of the car as it travels the 80 m.

(2)

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Q3.

The mass of a car is 1200 kg.

Calculate the resultant force on the car required to produce an acceleration of 0.8 m/s2.

(2)

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Q4.

Two students, Alice and Bob, carry out an experiment to measure the speed of cars.

Alice paces out the distance between two lamp posts.

She records:

'Distance between lamp posts = 20 paces'

Bob starts to count when a car passes the first lamp post. He stops counting when he thinks it has passed the second lamp post.

He records:

'My estimate for the time taken for the car to pass between the two lamp posts = 3'

Give three ways the students could improve their experimental procedure.

(3)

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(Total for question = 3 marks)

Q5.

Figure 10 shows two students investigating reaction times.

Student B supports his left hand on a desk.

Student A holds a ruler so that the bottom end of the ruler is between the finger and thumb of student B.

When student A releases the ruler, student B catches the ruler as quickly as he can with his left hand.

The investigation is repeated with the right hand of student B.

Figure 10

(a) Give a reason why it is better to have the 0 cm mark at the bottom of the ruler rather than at the top.

(1)

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(b) Give a reason why two students are needed for this investigation.

(1)

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(c) The students took five results for the left hand and five results for the right hand.

Figure 11 shows their results.

Figure 11

(i) Calculate the average distance dropped for the right hand. Give your answer correct to 2 significant figures.

(2)

distance = ........................................................... cm

(ii) Calculate the average time for the left hand.

Use the equation

(2)

average time = ........................................................... s

(d) Explain whether any of the readings are anomalous.

(2)

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(e) Give two ways that the students can improve the quality of their data, other than ignoring anomalous results.

(2)

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(f) Describe how the students could develop their investigation to investigate how reaction time changes with another variable.

(2)

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(Total for question = 12 marks)

Q6.

A car driver sees a rabbit on the road.

The driver makes an emergency stop after he sees the rabbit.

Figure 6 shows the speed of the car from the time the driver sees the rabbit until the car stops.

Figure 6

Calculate the distance that the car travels in the first 0.5 seconds.

(3)

distance = ........................................................... m

(Total for question = 3 marks)

Q7.

A student investigates the motion of a trolley along a horizontal runway using the apparatus in Figure 2.

Figure 2

A trolley is attached to a string passing over a pulley.

A block of metal hangs on the end of the string.

Each light gate measures the time it takes for the card to pass through the gate.

When the trolley is released, it moves along the track.

A computer measures the time it takes for the card to pass between each light gate.

Figure 3 shows a graph of acceleration against force for three trollies of different mass that are pulled along the runway.

The graphs for the trollies are labelled P, Q and R.

Figure 3

Use the information from the graph.

(i) Calculate the mass of trolley Q

(2)

mass of trolley Q = ........................................................... kg

(ii) Describe how the graph shows that trolley R has the greatest mass.

(2)

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(Total for question = 4 marks)

Q8.

(a) Here is the velocity-time graph for a car for the first 20 s of a journey.

(i) Calculate the change in velocity of the car during the first 5 s.

(1)

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(ii) Calculate the acceleration of the car during the first 5 s.

(2)

acceleration = ......................m/s2

(iii) State the size of the resultant force between 10 s and 15 s

(1)

.............................................................................................................................................. (b) The mass of a car is 1200 kg.

Calculate the resultant force on the car required to produce an acceleration of 0.8 m/s2.

(2)

.............................................................................................................................................. *(c) A car, travelling at 20 m/s, with just the driver inside takes 70 m to stop in an emergency. The same car is then fully loaded with luggage and passengers as well as the driver.

Explain why it will take a different distance to stop in an emergency from the same speed.

(6)

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(Total for Question = 12 marks)

Q1. No Examiner's Report available for this question Q2.

Many candidates failed to answer this correctly due to the following points;

i) Not recognising that a diagonal line on a distance time graph = constant speed and instead interpreting this section as acceleration.

ii) If candidate did correctly identify the first section as constant/ steady speed – many went on to describe the second section (less steep line) as acceleration not deceleration.

iii) Many candidates simply described the pattern of the graph rather than using specific terms e.g. as time increased, the distance increased.

Results Plus: Examiner Comments Vague descriptions of the graph. 0 marks.

Results Plus: Examiner Comments One of the responses that scored both marks for this question.

Results Plus: Examiner Comments This type of response from candidates was very common. 0 marks.

Results Plus: Examiner Comments Many candidates thought that the decrease in gradient represented an acceleration of the car. This candidate scored one mark for the first part of their response.

Results Plus: Examiner Tip Always write clearly and concisely.

Q3.

This was a straightforward calculation for most candidates. The most common error seemed to be incorrect use of the calculator by carrying out a division of 1200 by 0.8 to produce a result of 1500. As usual, candidates could score 1 mark if the substitution was correctly shown.

Results Plus: Examiner Comments This clearly laid out response scored 2 marks.

A mark was given for substituting the correct values into the equation.

Results Plus: Examiner Comments The expression 1200 Kg x 0.8 is correct for one mark. Unfortunately the candidate seems to have used the divide function on the calculator and so could not get the second mark.

Results Plus: Examiner Comments The candidate may have made the same mistake and pressed divide rather than multiply on the calculator. Unfortunately, there was no working shown and so no marks were scored.

Results Plus: Examiner Tip Always show your working.

Q4. No Examiner's Report available for this question Q5. No Examiner's Report available for this question

Q6. No Examiner's Report available for this question Q7. No Examiner's Report available for this question Q8.

aiii

Candidates should be aware that if they are asked to state a value then a calculation is not necessary. This question asked candidates to 'state the size' of the resultant force between 10s and 15s. The graph shows that the car had a constant velocity during this time and so the resultant force must be zero.

Results Plus: Examiner Comments The answer should be simply 0.

Results Plus: Examiner Tip You do not need to do a calculation if you are simply asked to 'state the size' of something.

ai-ii

For the first part of this question (i), candidates needed to subtract the starting velocity (0) from the velocity at 5s (8 m/s) to arrive at an answer of 8 m/s. Many candidates calculated the acceleration in this part by finding the gradient of the line.

In the second part (ii), candidates needed to divide the change in velocity in part (i) by the time taken (5s) to find the acceleration (1.6 m/s2). Provided that working was shown, examiners allowed full credit for an error carried forward from (i) into (ii).

Although the answer to part (i) is incorrect, the candidate has carried on to use the value to calculate acceleration and has shown the working. The examiner could clearly see that the candidate knows how to find acceleration and awarded 2 marks for part (ii).

Results Plus: Examiner Comments Candidates need to be clear about the difference between 'change in velocity' and 'rate of change in velocity' (ie acceleration).

Results Plus: Examiner Tip 'Calculate' does not always mean that you have to multiply or divide. It can also mean add or subtract.

b

This was a straightforward calculation for most candidates. The most common error seemed to be incorrect use of the calculator by carrying out a division of 1200 by 0.8 to produce a result of 1500. As usual, candidates could score 1 mark if the substitution was correctly shown.

Results Plus: Examiner Comments This clearly laid out response scored 2 marks.

A mark was given for substituting the correct values into the equation.

Results Plus: Examiner Comments The expression 1200 Kg x 0.8 is correct for one mark. Unfortunately the candidate seems to have used the divide function on the calculator and so could not get the second mark.

Results Plus: Examiner Comments The candidate may have made the same mistake and pressed divide rather than multiply on the calculator. Unfortunately, there was no working shown and so no marks were scored.

Results Plus: Examiner Tip Always show your working.

c

Most candidates realised that the extra passengers and luggage would increase the overall mass of the car. However, very many expressed this as an increase in weight rather than mass. This seemed to lead them towards considering downwards forces on the road and, very often, increase in friction. They then drew the conclusion that this would make the car stop more quickly in an emergency. There was a widespread misunderstanding that it was friction between the tyres and the road which was responsible for stopping the car when the brakes were applied. It was surprising that a large number of candidates thought that a heavily loaded car could stop more quickly than one with just the driver.

Candidates who correctly used the term 'increase in mass' very often went on to reason that the car would take a longer time to come to halt. This was sometimes nicely expressed in terms of momentum or kinetic energy and sometimes expressed in terms of forces and rate of change of velocity.

It was sometimes difficult for the examiner to decide whether 'takes longer to stop' referred to a longer time or a greater distance.

There were quite a few candidates who suggested that the passengers might distract the driver. They often went on to give a good description of how this could affect overall stopping distance by increasing the thinking distance. Examiners gave credit for this.

Results Plus: Examiner Comments This answer makes a correct statement about the mass or weight increasing when the car is fully loaded. This is a level 1 response. It then goes on to consider resistance and forces pulling the car down to arrive at a conclusion that the car will stop quicker than an unloaded car. This is incorrect and so cannot reach level 2. It scored only 2 marks.

Results Plus: Examiner Comments The candidate links the increase in mass with taking 'longer to stop'. It is not clear whether this is a longer time or a longer distance. The answer goes on to describe air

resistance and gravity which is not relevant in this situation. It then goes on to mention resultant forces, but, once again, this is not in the correct context. The examiner ignored the second and third sentences. The candidate eventually goes on to state that the lighter car takes a shorter time to stop without mentioning distance. This is a good level 2 response but does not quite make the links clear enough to reach level 3. The quality of written communication is appropriate. It scored 4 marks.

Results Plus: Examiner Comments Although it not clear what force is being referred to, the answer makes very good points about an increase in mass resulting in a longer time to stop and so a longer distance travelled. This is a level 3 response. The quality of written communication is appropriate for this level. It scored all 6 marks.

Mark Scheme Q1.

Q2.

Q3.

Answer Acceptable

answers Mark

substitution F = 1200 × 0.8 (1) evaluation (1) 960 (N)

full marks for correct answer with no working shown.

(2)

Q4.

Q5.

Q6.

Q7.

Q8.

Answer Acceptable

answers Mark

(a)(i) 8 – 0 (m/s) 8 (1)

(a)(ii) substitution 8 / 5 (1) evaluation (1) 1.6 (m/s2)

ecf from (i) full marks for correct answer (or ecf) with no working shown.

(2)

(a)(iii) 0 Nil / nothing / zero / (1)

none (no mark for no response)

(b) substitution F = 1200 × 0.8 (1) evaluation (1) 960 (N)

full marks for correct answer with no working shown.

(2)

Indicative Content Mark

QWC *(c) an explanation linking some of the following points: compared to a car with just the driver, a fully loaded car will

have a greater mass / be heavier

greater kinetic energy / momentum

experience the same braking force (when brakes are applied)

require a greater braking force (than available) to stop (in the same distance)

have a smaller acceleration / deceleration

take a longer time to come to rest (from given speed)

travel greater distance in this time

needs to do more work with same amount of force

use of relevant equations such as F = ma, work done = F × d

consequence of driver distractions (6)

Level 0 No rewardable content

1 1 - 2

a limited explanation using one idea from the indicative content eg fully loaded car is heavier.

in answer communicates ideas using simple language and uses limited scientific terminology

spelling, punctuation and grammar are used with limited accuracy

2 3 - 4

a simple explanation which links ideas from the indicative content eg it is heavier and so it takes a longer distance to stop

the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately

spelling, punctuation and grammar are used with some accuracy

3 5 - 6

a detailed explanation which links several ideas from the indicative content e.g. It has more momentum and so it will take a longer time to stop. This means that it will travel a further distance. The answer communicates ideas clearly and coherently uses a range of scientific terminology accurately

spelling, punctuation and grammar are used with few errors