Momentum and impulse
Momentum is a vector; choose and state a positive direction.
Read the lesson: Motion with constant acceleration
For constant mass, momentum is mv and impulse is the change in momentum. In a one-dimensional calculation, signed velocities carry the directions. Multiplying mass by speed alone loses information when motion reverses.
Total momentum is conserved for a system over an interval when the external impulse is zero or negligible. This does not mean kinetic energy is conserved in every collision. Account for both objects and the same chosen direction before and after the interaction.
Worked example
A 2 kg particle changes velocity from +3 m/s to −1 m/s. Find the impulse.
- Initial momentum is 2 × 3 = 6 kg m/s.
- Final momentum is 2 × (−1) = −2 kg m/s.
- Impulse is final minus initial: −2 − 6.
Answer: −8 N s, opposite to the chosen positive direction
Practise momentum and impulse
Course mapping
These specification references show where the topic occurs. The questions cover only some parts of each topic.
- 9FM0 · FM1 · Momentum and impulse: Momentum and impulse
- 7367 · mechanics · Momentum and collisions: Momentum and impulse
- H245 · mechanics · Momentum and impulse: Momentum and impulse
- H645 · Y421 · Momentum and impulse: Momentum and impulse
- H645 · Y431 · Momentum and impulse: Momentum and impulse
- 9FM0 · FM1 · Momentum and impulse: A one-dimensional collision with restitution
- 7367 · mechanics · Momentum and collisions: A one-dimensional collision with restitution
- H245 · mechanics · Momentum and impulse: A one-dimensional collision with restitution
- H645 · Y421 · Momentum and impulse: A one-dimensional collision with restitution
- H645 · Y431 · Momentum and impulse: A one-dimensional collision with restitution
Next practice: Scalar products and angles.