A shopping trolley is pushed along a flat supermarket floor. When the person stops pushing, the trolley decelerates and comes to rest. Explain why the trolley decelerates when the pushing force is removed, and state which of Newton's laws describes the trolley remaining at rest once it has stopped.

Eduqas GCSE Physics — 4.2 Forces, accelerations and Newton's laws of 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)

When the pushing force is removed, friction between the trolley wheels and the floor continues to act.
Friction acts opposite to the direction of motion, producing a net force on the trolley.
This unbalanced force causes the trolley to decelerate.
Once the trolley stops, Newton’s First Law applies – it remains at rest because no net force acts on it.

Examiner tips

  • Use the word ‘friction’ and state its direction relative to motion
  • Show that a net force causes deceleration
  • Mention Newton’s First Law for the final rest state
  • Keep answer concise and to the point

Common mistakes

  • Confusing friction with the pushing force, or saying friction is absent
  • Forgetting to state the direction of friction
  • Misidentifying the relevant Newton’s law (e.g., using the second law instead of the first)

Mark scheme (4 marks)

  1. When the pushing force is removed, friction (from the floor/wheels) still acts on the trolley
  2. Friction acts in the opposite direction to the trolley's motion
  3. There is a resultant (unbalanced) force on the trolley, causing it to decelerate
  4. Newton's First Law describes the trolley remaining at rest (an object remains at rest unless acted on by a resultant force)

Key terms in this question

decelerate

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