Say there was 2 collisions. There are 2 carts of identical mass. In the first case cart A starts at height h above the ground and crashes into cart B which is stationary on the flat ground. They stick together. In the second case, cart A starts at height h/2 above the ground, cart B starts at height h/2 above on the ground on the other side. They fall in opposite directions and collide and stick together. The problem asks that when the carts reach the flat ground, in which case is the magnitude of the total momentum greater. When they ask about the magnitude, in case 2, should the momentum be M(a)V(a) + M(b)V(b) = 2M(a)V(a) (which would be greater than case 1), or should I factor in the fact that they are traveling in opposite directions, in which case the total momentum would be zero? The second question asks whether the total energy lost in greater in case 1 or case 2. The energy lost would be greater in case 2 if the momentum was 2M(a)V(a).... but then again this goes to question 1. Thanks!