FRICTION AND BRAKING
3 marks · EasyA driver is travelling at 30 mph in dry conditions. The thinking distance for this speed is 9 m and the braking distance is 14 m.
Calculate the total stopping distance.
If the driver’s reaction time increases (for example, because they are tired), explain what will happen to the stopping distance.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 23 m
(b) The stopping distance will increase because the thinking distance will be longer if reaction time is greater. · must show states increase in stopping distance, links to increased thinking distance or time
Common mistakes: Omitting one distance; Failing to link increased reaction time with thinking distance
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Marking points
A1 (a) · 1 mark · Correct addition of thinking and braking distances: 9 m + 14 m = 23 m.
B1 (b) · 1 mark · States that the stopping distance increases if reaction time increases.
B2 (b) · 1 mark · Explains that this is because thinking distance increases with longer reaction time.
Worked solution
(a) Total stopping distance = thinking distance + braking distance = 9 m + 14 m = 23 m.
(b) If the driver’s reaction time increases, the thinking distance will become longer. Since stopping distance is the sum of thinking and braking distances, the total stopping distance will increase.