AS Daily A Level Physics question
In a lab, a 0.50 kg trolley glides on a near-frictionless track at 0.80 m/s to the right and collides with an identical 0.50 kg trolley at rest; they stick together. Immediately after the collision, what is the speed of the joined trolleys?
Answer
The correct answer is A.
Correct: A — 0.40 m/s to the right. A is correct because total momentum before (m × 0.80) equals total momentum after (2m × v), giving v = 0.80/2 = 0.40 m/s in the same direction. B is wrong because the speed cannot stay the same when the mass doubles if momentum is conserved. C is wrong because the total initial momentum is not zero, so they cannot come to rest. D is wrong because it comes from (incorrectly) conserving kinetic energy in a sticky collision, giving v ≈ 0.80/√2 ≈ 0.57 m/s, which does not apply here.