AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), 2020: Question 6

13 marks · Standard Demand difficulty · Extended Answer

Calculate a reduced speed limit and braking distance, and explain how reduced speed and lower vehicle mass affect stopping distance and collision risk.

Practise this question

Question

The question page contains four linked parts about road speed and stopping distance. Part 06.1 states that the speed limit on many roads in towns is 13.5 m/s and outside schools this is reduced by one-third, then asks for the reduced speed limit for 2 marks with answer lines. Part 06.2 says a reduced speed limit may reduce air pollution and asks for one other advantage for 2 marks. Part 06.3 includes a photograph labelled Figure 11 showing a roadside speed camera and a blurred car driving past; text says the camera recorded two images 0.70 s apart, the car travelled 14 m between images, and the maximum deceleration is 6.25 m/s squared, then asks for the minimum braking distance for 6 marks. Part 06.4 includes Figure 12, a photograph of the open back of a delivery van full of packages with labels pointing to the packages, and asks why the empty van has a shorter stopping distance than the full van when driven at the same speed, for 3 marks.
Question text

06 The speed limit on many roads in towns is 13.5 m/s

Outside schools this speed limit is often reduced by one-third.

06.1 Calculate the reduced speed limit.

[2 marks]

Reduced speed limit = m/s

06.2 A reduced speed limit may reduce air pollution.

Explain one other advantage of a reduced speed limit.

[2 marks]

06.3 Figure 11 shows a car being driven at a constant speed past a speed camera.

Figure 11

The camera recorded two images of the car 0.70 s apart.

*15* The car travelled 14 m between the two images being taken.

The maximum deceleration of the car is 6.25 m/s2

Calculate the minimum braking distance for the car at the speed it passed the

speed camera.

[6 marks]

Minimum braking distance =17 m

06.4 Figure 12 shows a delivery van full of packages.

*16* Figure 12

The driver delivers all the packages.

The empty van has a shorter stopping distance than the full van when driven at the

same speed.

Explain why.

[3 marks]

Mark scheme

Show the mark scheme The mark scheme is a table with rows for questions 06.1 to 06.4, columns for answers, extra information, marks, and AO/specification references. For 06.1 it awards marks for calculating 13.5 multiplied by two-thirds or subtracting one-third to give 9.0 m/s. For 06.2 it credits answers such as reduced stopping distance leading to less chance of collision, or less kinetic energy causing less injury. For 06.3 it gives method marks for using 14 = v × 0.70 to find v = 20 m/s, then applying the motion equation 0 squared minus 20 squared equals 2 times negative 6.25 times s to obtain s = 32 m, with minus signs ignored. For 06.4 it credits explanations that the brakes apply the same maximum force, a lower mass gives greater deceleration and shorter braking distance, or equivalently that lower mass means less kinetic energy and less work needed to stop, so the braking distance is less.

AO /

Question Answers Extra information Mark

Spec. Ref.

06.1 13.5 × 1 AO2

6.5.4.3

9.0 (m/s) allow 9 (m/s) 1

OR

13.5 × = 4.5 (1)

13.5 - 4.5 = 9.0 (m/s) (1)

06.2 reduced speed reduces allow reduces thinking / braking 1 AO1

stopping distance distance 6.5.4.3.2

6.5.4.3.3

means less chance of collision 1

OR

the car will have less kinetic

energy (1)

so less likely to cause injury in

the event of a collision (1)

06.3 14 = v × 0.70 1 AO2

6.5.4.1.2

14 1 6.5.4.1.5

v =

0.70

v = 20 (m/s) 1

02–202 = 2 × (–6.25) × s

s =

(2 × 6.25) 1

ignore minus signs throughout

s = 32 (m) 1

06.4 same maximum force applied by 1 AO2

the brakes

because mass is less there is a allow momentum for mass 1 13

greater deceleration AO1

braking distance is less 1

AO1

OR

6.5.2

reducing the mass reduced the

kinetic energy of the van (at a

given speed) (1)

less work needed to be done to

bring the van to a stop (1)

(force from the brakes is the

same) so braking distance is

less (1)

Total 13

How to answer it

Road Safety, Braking Distance and Motion
What this question tests
Calculating fractions and speed changes, explaining road safety advantages, using speed = distance ÷ time, using the braking equation, and linking mass, kinetic energy, force and braking distance.
Question 06.1 — Calculate the reduced speed limit

Part (a): Reduced speed limit outside schools

💡 Key knowledge

  • “Reduced by one-third” means take away 1/3 of the original speed.
  • That leaves 2/3 of the original speed.
  • Always keep the unit: m/s .

📐 Calculation: step-by-step

  1. Original speed = 13.5 m/s
  2. Reduced speed = 13.5 × 2/3
  3. 13.5 ÷ 3 = 4.5
  4. 4.5 × 2 = 9.0

Reduced speed limit = 9.0 m/s

Mark breakdown: 1 mark for using the correct fraction, 1 mark for the correct answer with unit.

❌ Common errors

  • Using 13.5 × 1/3 and stopping there — that gives the amount reduced, not the new speed.
  • Writing 4.5 m/s as the answer — this is only the reduction.
  • Forgetting the unit.

🧠 Exam technique

For “reduced by one-third”, think: new value = original × 2/3. This is a quick shortcut that avoids working out the part removed first.

Question 06.2 — One other advantage of a reduced speed limit

Part (b): Why lower speeds are safer

✅ Correct answers

  • Reduced speed reduces stopping distance, so there is less chance of a collision.
  • The car has less kinetic energy, so it is less likely to cause injury in a crash.
  • Reduced speed reduces thinking distance or braking distance.

💡 Key knowledge

  • Stopping distance = thinking distance + braking distance.
  • Kinetic energy increases with speed, so faster cars are more dangerous.
  • Examiners accept either a safety point or an energy point if explained clearly.

🧠 How to get the marks

For 2 marks, make two linked points. A good structure is:

lower speed → shorter stopping distance → less chance of collision

or

lower speed → less kinetic energy → less injury if a collision happens

❌ Common errors

  • Just saying “it is safer” without explaining why.
  • Mixing up stopping distance and braking distance.
  • Writing about pollution again — the question asks for a different advantage.

✅ Example full-mark response

“A reduced speed limit reduces stopping distance, so there is less chance of a collision.”

That would score full marks because it gives a clear cause-and-effect explanation.

Question 06.3 — Minimum braking distance

Part (c): Calculate the braking distance at the speed camera

📐 Step 1: Find the speed of the car

The car travels 14 m in 0.70 s .

  1. Use speed = distance ÷ time
  2. v = 14 ÷ 0.70
  3. v = 20 m/s

📐 Step 2: Use the equation for braking

Maximum deceleration = 6.25 m/s²

  1. Use v² = u² + 2as
  2. Final speed at stop = 0
  3. Initial speed = 20 m/s
  4. Acceleration is negative because it is braking, but the mark scheme allows ignoring minus signs.

0² = 20² + 2 × (-6.25) × s

So, s = 20² ÷ (2 × 6.25)

s = 32 m

🧠 Exam technique

  • Show the speed calculation first: it often earns a mark on its own.
  • Use the correct equation and substitute values carefully.
  • State the final answer with the unit m .
  • If your answer is different by a small amount because of rounding, show clear working.

❌ Common calculation traps

  • Using 14 ÷ 70 instead of 14 ÷ 0.70 .
  • Using the wrong equation, or forgetting to square the speed.
  • Putting 6.25 in as a positive acceleration without thinking about braking.
  • Forgetting the unit on the final answer.

✅ Mark-earning answer structure

  1. Calculate speed: 20 m/s
  2. Use the braking equation: 0² = 20² + 2 × (-6.25) × s
  3. Rearrange correctly
  4. Answer: 32 m
Question 06.4 — Why the empty van stops in a shorter distance

Part (d): Explain why the empty van has a shorter stopping distance

✅ Correct ideas from the mark scheme

  • The brakes apply the same maximum force.
  • Because the van is less massive when empty, it has greater deceleration.
  • So the braking distance is shorter.

💡 Key knowledge

  • At the same speed, a smaller mass means less kinetic energy.
  • Less kinetic energy means less work is needed to bring the van to rest.
  • If braking force stays the same, the stopping distance decreases.

🧠 Best exam wording

A strong answer usually includes a chain:

less mass → less kinetic energy → less work needed → shorter braking distance

or

same braking force + less mass → greater deceleration → shorter stopping distance

❌ Common errors

  • Saying the brakes are “stronger” when the van is empty — the force is the same.
  • Talking only about speed, even though speed is the same in both cases.
  • Not linking mass to kinetic energy or deceleration.

🧠 Examiner insight

Top answers did more than state “less mass means shorter stopping distance”. They explained why: the same braking force acts on a smaller mass, so the van slows more quickly, or less kinetic energy must be removed.

Overall exam focus

How this whole question is marked

💡 Knowledge to remember

  • Fractions of quantities: “reduced by one-third” means multiply by 2/3 .
  • speed = distance ÷ time
  • v² = u² + 2as
  • Less mass at the same speed gives less kinetic energy.

🧠 General technique

  • Always include units.
  • Show working clearly for calculation questions.
  • For explanations, use because / so / therefore to link ideas.
  • Give enough detail to earn the second mark, not just the first statement.

❌ Final reminders

  • Don’t confuse stopping distance with braking distance.
  • Don’t forget that “reduced by one-third” means the answer is 2/3 of the original.
  • Don’t stop after finding the distance removed.

Topics

Physics · P1: Energy · P5: Forces

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 2 (Higher), 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.