This key facts covers Conservation of Momentum — Worked Examples within Momentum for GCSE Physics. Revise Momentum in Forces for GCSE Physics with 13 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 4 of 12 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
🔢 Conservation of Momentum — Worked Examples
Example 1: Two cars collide and stick together (inelastic)
Car B: mass = 1500 kg, velocity = 0 m/s (stationary)
Momentum before = (1000 × 20) + (1500 × 0) = 20,000 kg m/s
Momentum after = (1000 + 1500) × v = 2500v
2500v = 20,000
v = 8 m/s (combined, moving in original direction)
Example 2: Explosion (person jumps off skateboard)
Person (60 kg) jumps left at 3 m/s
Momentum of person = 60 × (-3) = -180 kg m/s
Momentum of skateboard = +180 kg m/s
Skateboard (5 kg) → v = 180/5 = 36 m/s right
Quick Check: A 3 kg ball moves at 4 m/s and collides with a stationary 5 kg ball. They stick together. What is their combined velocity?
Momentum before = 3 × 4 = 12 kg m/s. Momentum after = (3 + 5) × v = 8v. 8v = 12, so v = 1.5 m/s in the original direction. Total momentum is conserved.
Practice questions for Momentum
What is the equation for momentum?
Explain what is meant by saying momentum is a vector quantity.