PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
Two identical low-friction carts A and B, each of mass 0.50 kg, rest side-by-side on a horizontal track. A compressed spring is held between the carts so that the spring pushes on both carts when released. While the spring is compressed, a small horizontal breeze exerts a constant force of 0.20 N toward the +x direction on cart A only. At time t = 0 the spring is released and returns to its relaxed length in 0.30 s, after which the breeze continues to act on cart A.
Assume the track is frictionless and neglect any external forces other than the breeze.
(a) During the 0.30 s interval while the spring is expanding, describe all horizontal forces acting on each cart and state their directions.
(b) Consider the system consisting of both carts and the spring. Determine whether the horizontal momentum of this system is conserved during 0 ≤ t ≤ 0.30 s. Justify your answer in terms of the forces identified in part (a).
(c) Now consider the system consisting of cart B only. Explain whether the horizontal momentum of cart B changes during 0 ≤ t ≤ 0.30 s, and identify the physical quantity responsible for any change.