AS Daily A Level Physics question
On a level, low-friction track, a 2.0 kg trolley moving at 0.60 m s−1 collides and couples with a stationary 0.80 kg trolley. Ignoring external forces, which option gives their common speed immediately after impact and the type of collision?
Answer
The correct answer is C.
Correct: C — 0.43 m s−1; inelastic. A is wrong because it labels the collision elastic (they couple, so kinetic energy is not conserved) and the speed is too low from an incorrect momentum calculation. B is wrong because although coupling implies inelastic, 0.25 m s−1 comes from an erroneous averaging/dividing by the wrong total mass. C is correct: total momentum 2.0×0.60 = 1.20 kg m s−1 shared by 2.8 kg gives v ≈ 1.20/2.8 ≈ 0.43 m s−1, and coupling means kinetic energy decreases, so inelastic. D is wrong because it calls the event elastic even though sticking together cannot conserve kinetic energy.