FRICTION AND BRAKING
3 marks · NormalA car and a heavy lorry both apply their brakes with the same force while travelling at the same speed on a dry road. The lorry travels further before stopping.
Explain why the lorry takes longer to stop than the car, even though the braking force is the same.
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The lorry has a larger mass, so the same braking force causes a smaller deceleration (a = F/m). This means it slows down less quickly and takes longer and travels further before stopping.
Must show: reference to mass, a = F/m, smaller deceleration means further distance
Also accept: Reference to Newton's second law in words
Common mistakes: Saying lorries are slower without reference to mass or force; Ignoring braking force and mass relationship
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Recognises the lorry has more mass
M2 · 1 mark · States or uses the relation a = F/m (Newton's second law)
M3 · 1 mark · Links smaller deceleration to a greater stopping/braking distance
Worked solution
The lorry has a much larger mass than the car. According to Newton's second law (), the same braking force will produce less deceleration in the lorry than in the car. As a result, the lorry slows down more slowly and travels further before stopping.