FRICTION AND BRAKING
3 marks · HardA driver needs to stop suddenly when a traffic light turns red. The car is moving at a higher speed than usual, and the driver is very tired.
Describe how the driver’s tiredness and the higher speed affect the thinking and braking distances.
Explain the effect of these factors on the total stopping distance.
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(a) Tiredness increases reaction time, which increases thinking distance. Higher speed also increases thinking distance, since the car travels faster during the reaction time. Higher speed increases braking distance, because the car has more kinetic energy to lose before stopping. · must show effect of tiredness on thinking distance, effect of higher speed on thinking distance, effect of higher speed on braking distance
(b) Both thinking distance and braking distance increase, so the total stopping distance increases significantly. · must show stopping distance increases due to both effects
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Marking points
B1 (a) · 1 mark · States that tiredness increases thinking distance (by increasing reaction time)
B2 (a) · 1 mark · States that higher speed increases both thinking distance and braking distance
B3 (b) · 1 mark · States or explains that stopping distance increases due to both effects
Worked solution
a) Tiredness makes the driver’s reaction time longer, so the thinking distance increases. Higher speed increases the distance travelled during the reaction time (thinking distance) and also means the car takes longer to stop (braking distance), since more kinetic energy must be removed.
b) Because both thinking and braking distances increase, the total stopping distance is much larger.