PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
Two identical low-friction carts, A and B, are on a straight, horizontal track. Cart A is initially moving toward cart B, which is at rest. The collision that follows is known to conserve the total kinetic energy of the two-cart system.
(a) Describe the physical criterion that distinguishes a collision that conserves total kinetic energy from one that does not.
(b) Without carrying out any numerical calculations, predict the directions of motion of carts A and B after they collide. Justify your prediction using appropriate physical reasoning.
(c) After the collision, the speed of cart A is observed to be nearly zero while cart B moves away with a speed approximately equal to A’s original speed. Explain how this observation is consistent with conservation of both momentum and kinetic energy, even though the kinetic energies of the individual carts have changed.
(d) Suppose instead that cart A has twice the mass of cart B but the same initial speed as in the original scenario, while cart B remains at rest. Qualitatively describe how the post-collision motion of each cart in this new scenario would differ from the motion you predicted in part (b). Provide physical reasoning for your answer.