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AS Daily A Level Physics question

2026-02-25 OCR A Conservation of momentum (1D) OCR-A Module 3.5: Newton’s laws and momentum — conservation of linear momentum in 1D (AS) OCR-A Module 3.5: Momentum and impulse (AS) — p = mv; impulse as change in momentum

On a near-frictionless air track, a 0.30 kg glider moves to the right at 2.4 m/s and collides with, then sticks to, a stationary 0.60 kg glider. Assuming no significant external horizontal forces during the brief impact, which statement must be true immediately after the collision?

  1. A The joined gliders move at about 0.40 m/s to the right.
  2. B The joined gliders move at about 0.80 m/s to the right. (correct)
  3. C The joined gliders move at about 1.2 m/s to the right.
  4. D The joined gliders remain at rest immediately after impact.

Answer

The correct answer is B.

Correct: B — The joined gliders move at about 0.80 m/s to the right. A is incorrect because 0.40 m/s would give only 0.36 kg m/s of momentum, not matching the initial 0.72 kg m/s. B is correct: using momentum conservation, v = (0.30 × 2.4)/(0.30 + 0.60) = 0.72/0.90 ≈ 0.80 m/s to the right. C is incorrect because 1.2 m/s comes from dividing by only the struck mass (0.60 kg), ignoring that both masses move together after sticking. D is incorrect because stopping would require zero total initial momentum; energy loss in an inelastic collision does not remove momentum without external forces.

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