An open freight car rolls friction-free along a horizontal track in vertically pouring rain.As water accumulates in the car,its 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 (car + water), the total momentum of the system 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 Track