FRICTION AND BRAKING
3 marks · NormalA driver is travelling at night when it begins to rain heavily. Describe and explain how both the thinking distance and the braking distance are affected, giving a reason for each.
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Thinking distance may increase because the driver could take longer to notice hazards due to poor visibility in heavy rain. Braking distance increases because the wet road reduces friction between the tyres and the road surface, so the vehicle takes longer to stop.
Also accept: Thinking distance might not change if the driver's reaction is unaffected, but poor visibility can increase reaction time. Braking distance always increases in wet conditions.
Common mistakes: Saying only that both distances 'increase' without reasons.; Confusing thinking distance and braking distance causes.
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States that thinking distance may increase due to poor visibility or driver taking longer to see hazards.
B1 · 1 mark · States braking distance increases because of reduced friction on the wet road.
B1 · 1 mark · Gives valid scientific reasons for both changes (poor visibility/reaction; reduced friction).
Worked solution
In heavy rain at night, thinking distance may increase because the driver takes longer to spot hazards due to poor visibility.
Braking distance increases because the wet road surface decreases the friction force between the tyres and the road, so the car takes longer to stop.