Collisions

Revise Collisions for Mechanics 2 WME02 (A2 Level) — revision notes and instant AI marking.

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Edexcel IAL Mechanics 2 (WME02)

Collisions

The big idea: In every collision momentum is conserved; Newton's law of restitution supplies the second equation you need.

Summary — What This Chapter Covers

Impulse = change in momentum, I = m(v − u), as vectors.
Conservation of momentum in a direct impact.
Newton's law of restitution: speed of separation = e × speed of approach (0 ≤ e ≤ 1).
Impact with a wall: rebound speed = e × approach speed.

1. Impulse and Momentum as Vectors

Impulse

I = m(v − u)

Impulse and momentum are vectors: add impulse/m to the velocity component by component.

Worked Example

A 0.5 kg ball moving with velocity (3i + 4j) m s⁻¹ receives an impulse (−2i + j) N s. Find its new velocity.

2. Direct Impact and Newton's Law of Restitution

Restitution

Two equations, two unknowns

Draw before/after diagrams with all velocities in the same positive direction. Momentum gives one equation, restitution the other.

Worked Example

A (2 kg, 5 m s⁻¹) catches B (3 kg, 2 m s⁻¹) moving the same way; e = 0.5. Find their speeds after impact and the loss of KE.

3. Successive Impacts

Successive impacts

Collision after collision

Memorise

Momentum

Conserved in every impact

Restitution

separation = e × approach

Wall

rebound = e × approach

KE

Lost unless e = 1

Common Mistakes

Sign errors

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Collisions

Collisions

I = m(v − u)

Two equations, two unknowns

Collision after collision

Momentum

Restitution

Wall

KE

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