AQA GCSE Physics (8463), Higher tier · Forces › Forces and motion › Forces and braking
Practise Factors affecting braking distance. 11 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
(c)Answer: There is less friction between tyres and road, so the braking force and deceleration are smaller.
there is less friction (grip) between the tyres and the road
so the braking force is smaller / the deceleration is smaller
Question 2Medium3 marks
A car with a roof rack loaded with luggage has a much greater mass than the same car when empty. Both have identical brakes.
Explain why the loaded car needs a greater braking distance than the empty car, when braking from the same speed with the same braking force.[3]
Show the answer and mark scheme
Answer: More mass means more kinetic energy at the same speed; with the same braking force, more distance is needed to do the extra work removing it.
the loaded car has a greater mass, so (for the same speed) it has more kinetic energy
work done by the brakes = braking force × braking distance; the brakes must do more work to remove this greater kinetic energy
since the braking force is the same, a greater distance is needed to do this extra work, so the braking distance is greater
Question 3Hard9 marks
Use these typical values for a car on a dry road: reaction time of the driver ~0.7 s maximum braking deceleration ~7 m/s2
(a) Estimate the stopping distance of a car travelling at a typical town speed of 13 m/s. Use the Physics Equations Sheet.[3]
(b) Estimate the stopping distance of a car travelling at a typical motorway speed of 31 m/s.[2]
(c) The motorway speed is about 2.4 times the town speed, but the stopping distance is more than 4 times as great. Explain why.[2]
(d) On an icy road the maximum braking deceleration is about one quarter of the value on a dry road. Explain what this means for a driver travelling at 31 m/s on an icy road.[2]
Show the answer and mark scheme
(a)Answer: 21 m
thinking distance = 13 × 0.7 = 9.1 (m)
braking distance = 132 ÷ (2 × 7) = 12 (m)
stopping distance = 21 (m)
(b)Answer: 90 m
(31 × 0.7) + 312 ÷ (2 × 7) = 21.7 + 68.6
90 (m)
(c)Answer: Braking distance ∝ speed², so it increases by about 2.4² ≈ 5.7 times, while thinking distance increases 2.4 times.
thinking distance is proportional to speed, but braking distance is proportional to (speed)2
so the braking distance increases by a factor of about 2.42 ≈ 5.7
(d)Answer: The braking distance is about four times longer (≈ 275 m), so the driver must slow down and leave a much bigger gap.
the braking distance is about four times greater (about 275 m)
so the driver should travel much more slowly / leave a much bigger gap to the vehicle in front