🎯 Common Question Types:
- Calculate a change in momentum from mass and velocities (2 marks)
- Calculate average force during a collision (2-3 marks)
- Explain how crumple zones / airbags reduce force (3 marks)
- Distinguish elastic from inelastic collision (2 marks)
- Calculate the time a force acts for, from force and change in momentum (2 marks)
📝 Key Command Words:
- Calculate: Show F = Δp ÷ t (or Δp = F × t); include units (N, s, kg m/s)
- Explain: Use the "increasing time → decreasing force" chain of reasoning
- Suggest: Apply the physics principle to an unfamiliar context
- State: "Momentum is always conserved; kinetic energy is only conserved in elastic collisions"
⚠️ Common Mistakes to Avoid:
- Mixing up force (N) and momentum (kg m/s): force is the rate of change of momentum, not the momentum itself
- Forgetting to include direction in momentum change calculations
- Saying kinetic energy is conserved in all collisions — it is ONLY conserved in elastic collisions
- Forgetting to divide by the time: force = change in momentum ÷ time, not just the change in momentum
This exam tips covers Exam Tips: Force and Collisions within Force & Collisions for GCSE Physics. Revise Force & Collisions in Forces for GCSE Physics with 10 exam-style questions and 10 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 5 of 7 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Practice questions for Force & Collisions
Which equation links force, change in momentum and time?
Explain how an airbag reduces the risk of injury to a driver in a collision.
Quick recall flashcards
Force and Change in Momentum
Change in momentum = force × time (Δp = F × t)
Force and Change in Momentum
Change in momentum = final momentum minus initial momentum (Δp = mv − mu), measured in kg m/s