A cyclist is travelling along a straight, level road. The cyclist stops pedalling and the bicycle decelerates to a stop. Explain why the bicycle decelerates after the cyclist stops pedalling.

Edexcel GCSE Physics (1PH0) — 2.2 Forces and motion · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

1. When the cyclist stops pedalling the forward driving force from the chain and pedals disappears.
2. The bicycle is still subject to resistive forces such as friction between the tyres and the road, air resistance and drag.
3. With no forward force, the resistive forces are unbalanced – the resultant force is now directed opposite to the motion.
4. According to Newton’s second law a force opposite to the direction of motion produces a negative acceleration, so the bicycle decelerates until it stops.

Examiner tips

  • Use the word ‘resistive’ to show you know the forces involved.
  • Show the chain of reasoning: loss of driving force → unbalanced resistive forces → deceleration.
  • Mention Newton’s second law explicitly.
  • Keep the answer concise – one sentence per point.

Common mistakes

  • Confusing friction with air resistance or not naming both.
  • Saying the bicycle ‘slows down’ without linking it to the unbalanced force.
  • Forgetting to state that the forward force from pedalling is removed.

Mark scheme (4 marks)

  1. Friction / air resistance / drag acts on the bicycle (in the opposite direction to motion)
  2. There is no longer a driving / forward force (from the pedalling)
  3. The resultant force on the bicycle is not zero / is unbalanced (in the direction opposing motion)
  4. A resultant force in the opposite direction to motion causes deceleration / causes the bicycle to slow down (Newton's second law)

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