🎯 Common Question Types:
- Calculate momentum of an object (1-2 marks)
- Use conservation of momentum to find velocity after collision (3-4 marks)
- Explain why total momentum is conserved in a collision (3 marks)
- Explosion: find velocity of one piece given mass and velocity of other (3 marks)
📝 Key Command Words:
- Calculate: Show p = mv clearly; for collisions write "before = after"
- State: "Total momentum is conserved" — say it explicitly
- Explain: Link to Newton's Third Law — equal/opposite forces, same time
- Determine direction: Use positive/negative sign convention
⚠️ Common Mistakes to Avoid:
- Forgetting momentum is a vector — direction (sign) is essential
- Using mass in grams instead of kg
- Confusing speed (scalar) with velocity (vector) in p = mv
- Claiming kinetic energy is conserved in all collisions — only elastic ones
Quick Check: A 0.5 kg ball moves at 6 m/s to the right and a 2 kg ball moves at 1 m/s to the left. What is the total momentum of the system? (Take right as positive.)
Ball 1 momentum = 0.5 × 6 = +3 kg m/s. Ball 2 momentum = 2 × (-1) = -2 kg m/s. Total = 3 + (-2) = +1 kg m/s to the right. Direction matters — always assign signs before calculating.
This exam tips covers Exam Tips for Momentum within Momentum for GCSE Physics. Revise Momentum in Forces for GCSE Physics with 15 exam-style questions and 6 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 11 of 12 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Practice questions for Momentum
What is the equation for momentum?
Explain what is meant by saying momentum is a vector quantity.