AQA GCSE Combined Science: Trilogy Physics Paper 2 (Foundation), 2023: Question 2
8 marks · Standard Demand difficulty · Short Answer
Interpret a distance-time graph to determine braking distance and calculate deceleration using a given formula.
Practise this questionQuestion
Question text
02 A car contains a device called a black box. The black box records the distance
travelled and the time taken for each journey.
Figure 3 shows the distance–time graph for part of a journey.
Figure 3
02.1 Which feature of Figure 3 shows that the car travels at a constant speed for the
first 4 seconds?
[1 mark]
Tick ( ) one box.
The line becomes horizontal.
The line goes through the origin.
The line is straight. 11
02.2 After 4 seconds the driver applied the brakes and the car slowed down and stopped.
The distance the car travelled after the brakes were applied is called the
braking distance.
Determine the braking distance of the car.
*10* Use Figure 3.
[2 marks]
Braking distance = m
The black box also records the deceleration of the car.
02.3 As the car decelerates, the velocity of the car changes by 16 m/s.
The car decelerates for 2.5 seconds.
Calculate the deceleration of the car.
Use the equation:
change in velocity
deceleration =
time taken
[2 marks]
12Deceleration = m/s2
02.4 If the black box records large decelerations, it identifies that the driving may
be dangerous.
Why can large decelerations be dangerous?
[2 marks]
Tick ( ) two boxes.
*11* The brakes on the car can overheat.
The driver may lose control of the car.
The force applied by the brakes is very small.
The reaction time of the driver increases.
The thinking distance is very short.
02.5 The black box monitors the speed of the car.
Describe how speed affects braking distance.
[1 mark]
Mark scheme
Show the mark scheme
Question 2
AO /
Question Answers Extra information Mark
Spec. Ref.
02.1 the line is straight 1 AO2
6.5.4.1.4
AO /
Spec. Ref.
02.2 64 and 84 read from graph 1 AO3
6.5.4.1.4
braking distance = 20 (m) do not accept if readings from 1
the graph are incorrect
AO /
Spec. Ref.
02.3 16 1 AO2
a = 6.5.4.1.5
2.5
a = 6.4 (m/s2) ignore negative signs 1
AO /
Spec. Ref.
02.4 the brakes on the car can 1 AO1
overheat 6.5.4.3.4
the driver may lose control of 1
the car
AO /
Spec. Ref.
02.5 the greater the speed the 1 AO1
greater the braking distance 6.5.4.3.1
Total Question 2 8
How to answer it
Distance, Speed, and Braking Safety
What this question tests
This question assesses your ability to interpret distance-time graphs, calculate deceleration using a provided formula, and understand the safety implications of braking forces and speed.
Identifying Constant Speed
Correct Answer
✅ The line is straight.
Key Knowledge
- On a distance-time graph, the gradient (slope) represents the speed.
- A straight line has a constant gradient, meaning the speed is not changing.
Exam Technique
Don't confuse distance-time graphs with velocity-time graphs! On a velocity-time graph, a straight diagonal line means constant acceleration. Always check the axis labels first.
Determining Braking Distance
Step-by-Step Calculation
- Identify start of braking: At 4 seconds, the distance is 64 m.
- Identify end of journey: The car stops when the line becomes horizontal. At this point, the distance is 84 m.
- Calculate the difference: 84 m - 64 m = 20 m.
Mark 2: Correct final answer (20 m).
Common Errors
❌ Reading the total distance: Many students simply write "84 m". This is the total distance for the whole journey, not just the distance travelled while braking.
Calculating Deceleration
Calculation Steps
Formula: deceleration = change in velocity / time taken
- Substitute values: 16 / 2.5
- Final Answer: 6.4 m/s²
Mark 2: Correct calculation.
Examiner Insight
The mark scheme says to ignore negative signs. In physics, deceleration is technically a negative acceleration, but if the question asks for "deceleration," a positive number is usually expected as the word "deceleration" already implies slowing down.
Dangers of Large Decelerations
Correct Answers (Tick Two)
- ✅ The brakes on the car can overheat.
- ✅ The driver may lose control of the car.
Key Knowledge
When brakes are applied, friction between the brake pads and the wheels transfers kinetic energy into thermal energy. If this happens too quickly (large deceleration), the temperature can rise high enough to cause "brake fade" or failure.
Speed and Braking Distance
Correct Answer
The greater the speed, the greater the braking distance.
Key Knowledge
Braking distance is proportional to the square of the speed. If you double your speed, your braking distance actually increases by four times (2² = 4).
Common Errors
❌ Confusing Thinking and Braking: Speed affects both, but this question specifically asks for braking distance. Avoid talking about reaction times here, as speed doesn't change how fast your brain works, only how far the car travels while you think!
Topics
Physics · P5: Forces
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 2 (Foundation), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.