A child drags a sledge across a flat, snowy field using a horizontal rope. The snow exerts a friction force on the sledge. Explain why work is done on the sledge by the applied force, and describe what happens to the energy transferred against friction.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
1. Work is done by the applied force because the force causes the sledge to move, giving it a displacement in the direction of the force.
2. The amount of work is equal to the applied force multiplied by the distance over which it acts.
3. The friction force also does work on the sledge, but in the opposite direction to the motion.
4. The energy transferred against friction is converted into heat, raising the temperature of the sledge and the snow.
2. The amount of work is equal to the applied force multiplied by the distance over which it acts.
3. The friction force also does work on the sledge, but in the opposite direction to the motion.
4. The energy transferred against friction is converted into heat, raising the temperature of the sledge and the snow.
Examiner tips
- Show the force–displacement relationship for work, then state the formula W=F×d.
- Explain that friction does negative work and that the energy becomes heat.
- Use UK spelling and correct terminology (work, friction, heat).
Common mistakes
- Confusing the direction of work with the direction of force; forgetting that work is only done when there is displacement in the force direction.
- Treating friction as a force that adds energy instead of dissipating it.
- Using the wrong formula (e.g., W=F×θ) or omitting the distance term.
Mark scheme (4 marks)
- Work is done because a force causes the sledge to move / there is displacement in the direction of the applied force
- Work done is equal to force multiplied by distance moved (in the direction of the force)
- Work is done against friction / the friction force does work on the sledge
- Energy transferred against friction causes a rise in temperature / is transferred as heat/thermal energy to the sledge and snow
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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