Pushing a Cart 1

Consider two carts, of masses m and 2m, at rest on an air track. If you push first one cart for a certain amount of time and then the other for the same length of time, exerting equal force on each, the momentum of the light cart is

A) four times the momentum of the heavy cart.

B) twice the momentum of the heavy cart.

C) equal to the momentum of the heavy cart.

D) half the momentum of the heavy cart.

Solution: C. Change in momentum is equal to force times time, according to the impulse-momentum theorem. The initial momentums of the carts are equal, the forces on the carts are equal, and the times over which the forces act are equal, so the final momentums of the two carts are equal.