A motorcyclist is travelling along a road when a pedestrian steps out ahead. Explain why the stopping distance of the motorcycle increases when the motorcyclist is tired.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Stopping distance is made up of two parts: thinking distance and braking distance. A typical human reaction time is between 0.2 and 0.9 seconds.
Model answer (5 marks)
Tiredness increases the motorcyclist’s reaction time.
A longer reaction time means the motorcycle continues to travel at full speed for a greater period before the brakes are applied.
During this extra time the thinking distance therefore increases.
The total stopping distance is the sum of the thinking distance and the braking distance.
Because the thinking distance has increased, the overall stopping distance is greater.
A longer reaction time means the motorcycle continues to travel at full speed for a greater period before the brakes are applied.
During this extra time the thinking distance therefore increases.
The total stopping distance is the sum of the thinking distance and the braking distance.
Because the thinking distance has increased, the overall stopping distance is greater.
Examiner tips
- State the effect of tiredness on reaction time first.
- Explain how a longer reaction time increases thinking distance.
- Show that stopping distance = thinking + braking distance.
- Conclude that the overall stopping distance rises.
Common mistakes
- Confusing reaction time with braking time.
- Failing to link increased reaction time to increased thinking distance.
- Using vague terms like ‘slower’ instead of ‘longer reaction time’.
Mark scheme (5 marks)
- Tiredness increases the driver's reaction time
- A longer reaction time means the motorcycle travels further before the brakes are applied
- Thinking distance increases (because the motorcycle is still moving at full speed during the reaction time)
- Stopping distance is the sum of thinking distance and braking distance
- So the overall stopping distance is greater (because thinking distance has increased)
Key terms in this question
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