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 (car plus the accumulated water) must remain constant. Since momentum is the product of mass and velocity, an increase in the mass (due to accumulating water) must result in a decrease in velocity to keep the momentum constant.

An Open Freight Car Rolls Friction Free Along a Horizontal