AQA GCSE Physics (8463), Higher tier · Forces › Forces and motion › Forces and braking
Practise Braking forces and deceleration. 14 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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What happens to the temperature of the brakes?
It increases.
A car’s brakes exert a force of 4500 N over a distance of 15 m. Calculate the work done by the brakes. Use the equation: work done = force × distance
67 500 J
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
(a) When the brakes of a moving car are applied, work is done by the friction force between the brakes and the wheels. What happens to the kinetic energy of the car? Tick (✓) one box.[1]
It decreases
It increases
It stays the same
(b) What happens to the temperature of the brakes?[1]
(c) The brakes of a car exert a braking force of 6000 N while the car travels 20 m. Calculate the work done by the brakes. Use the equation: work done = force × distance[2]
Show the answer and mark scheme
(a)Answer: It decreases
(b)Answer: It increases.
it increases
(c)Answer: 120 000 J
W = 6000 × 20
120 000 (J)
Question 2Medium7 marks
A car of mass 1200 kg is travelling at 15 m/s. The driver brakes and the car stops in a braking distance of 18 m.
(a) Calculate the kinetic energy of the car before braking.[2]
(b) Calculate the average braking force.[3]
(c) Describe the energy transfer that takes place as the car brakes.[2]
Show the answer and mark scheme
(a)Answer: 135 000 J
Ek = 0.5 × 1200 × 152
135 000 (J)
(b)Answer: 7500 N
work done by the brakes = kinetic energy lost = 135 000 J
135 000 = F × 18
F = 7500 (N)
(c)Answer: Work done by friction in the brakes transfers energy from the car’s kinetic store to the thermal store of the brakes.
work done by the friction force (between the brakes and the wheels) reduces the kinetic energy of the car
energy is transferred to the thermal energy store of the brakes / the temperature of the brakes increases
Question 3Hard7 marks
A car of mass 1500 kg travelling at 25 m/s brakes to a stop. 80% of the car’s kinetic energy is transferred to the thermal energy stores of its four brake discs. Each disc has a mass of 6.0 kg. The specific heat capacity of the disc material is 460 J/kg °C.
(a) Calculate the kinetic energy of the car before braking.[2]
(b) Calculate the increase in temperature of the brake discs. Assume that the energy is shared equally between the four discs. Use the Physics Equations Sheet.[3]
(c) Explain why braking repeatedly while driving down a long, steep hill can be dangerous.[2]
Show the answer and mark scheme
(a)Answer: 468 750 J
Ek = 0.5 × 1500 × 252
468 750 (J)
(b)Answer: 34 °C
energy transferred to the discs = 0.80 × 468 750 = 375 000 (J)
375 000 = (4 × 6.0) × 460 × Δθ
Δθ = 34 (°C)
(c)Answer: The brakes may overheat and become less effective, so the car takes longer to stop.
the brakes can overheat / get very hot
so the brakes become less effective / the braking force decreases, so the braking distance increases