An open freight car rolls friction free along a horizontal track in a pouring rain that falls vertically. As water accumulates in the car, the car's speed

Question

Quizplus · Accepted Answer

As water accumulates in the car, its mass increases. According to the principle of conservation of momentum, if no external horizontal forces act on the system, the total momentum of the system must remain constant. Since momentum is the product of mass and velocity, as the mass of the car increases, its velocity must decrease to keep the momentum constant.

An Open Freight Car Rolls Friction Free Along a Horizontal