A cyclist is riding along a road when they spot a hazard ahead and apply the brakes to stop. Explain how the cyclist's speed affects both the thinking distance and the braking distance.

OCR GCSE Physics A: Gateway Science (J249) — P8 Global challenges · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A cyclist travelling at a higher speed takes a much greater distance to stop compared with a cyclist travelling at a lower speed.

Model answer (4 marks)

Thinking distance increases with greater speed because the reaction time stays the same but the cyclist covers more ground in that fixed time.
Braking distance increases with greater speed because there is more kinetic energy (and momentum) to remove, so the braking force must act over a greater distance.

Examiner tips

  • Use the word ‘because’ to link cause and effect. Show the two distances separately. Mention reaction time for thinking distance and kinetic energy for braking distance.

Common mistakes

  • Confusing thinking distance with braking distance. Using vague phrases like ‘more distance’ without explaining why. Omitting the role of reaction time or kinetic energy.

Mark scheme (4 marks)

  1. Thinking distance increases with greater speed
  2. Because the reaction time stays the same but the cyclist covers more ground in that fixed time
  3. Braking distance increases with greater speed
  4. Because there is more kinetic energy / momentum to remove, so the braking force must act over a greater distance

Key terms in this question

thinking distance · braking distance

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