AS Daily A Level Physics question
On a nearly frictionless air track, a 0.50 kg glider moves at 2.0 m s−1 to the right and collides head-on with a 1.50 kg glider moving at 0.50 m s−1 to the left. The gliders latch together on impact. Which option gives their common velocity immediately after the collision?
Answer
The correct answer is D.
Correct: D — 0.13 m s−1 to the right. Total momentum before is (0.50×2.0) + (1.50×−0.50) = 1.00 − 0.75 = +0.25 kg m s−1; total mass after sticking is 2.00 kg, so v = 0.25/2.00 ≈ 0.13 m s−1 to the right. A is wrong because taking the heavier glider’s initial speed and direction ignores conservation of momentum; the net momentum is to the right, not the left. B is wrong because 0.25 is the net momentum, not the final speed—this omits dividing by the total mass. C is wrong because the magnitude is about right but the direction must be to the right since the net momentum is positive. D is the only option consistent with 1D momentum conservation in both magnitude and direction.