FRICTION AND BRAKING
4 marks · NormalExplain how each of the following factors affects the braking distance of a vehicle. (a) The mass of the vehicle (b) The speed of the vehicle (c) The condition of the road surface (d) The condition of the tyres
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(a) A greater mass means a longer braking distance because more force is required to slow down a heavier vehicle.
(b) A higher speed increases braking distance, because the vehicle has more kinetic energy and takes longer to stop.
(c) A poor road surface (wet, icy or muddy) reduces friction, increasing the braking distance.
(d) Worn or poorly inflated tyres reduce friction with the road, making braking distance longer.
Also accept: Answers in any clear scientific form explaining each effect.
Common mistakes: Only listing factors with no explanation.
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Marking points
B1 (a) · 1 mark · Explains that greater mass increases braking distance.
B1 (b) · 1 mark · Explains that higher speed increases braking distance.
B1 (c) · 1 mark · Explains that poor road surface (wet/icy) increases braking distance due to reduced friction.
B1 (d) · 1 mark · Explains that worn/poorly inflated tyres increase braking distance due to reduced friction.
Worked solution
(a) A greater mass means there is more kinetic energy to remove, so the same braking force takes longer to stop the vehicle.
(b) Higher speed means the vehicle has much more energy, so braking distance increases (proportionally to the square of speed for constant force).
(c) A wet, icy or uneven road gives less friction, so the tyres slip and the car travels further.
(d) Bald or poorly inflated tyres cannot grip well, again reducing friction and lengthening the distance needed to stop.