An open train car moves with speed 15 m/s on a flat frictionless railroad track, with no engine pulling the car. It begins to rain. The rain falls straight down and begins to fill the train car.

Question

An open train car moves with speed 15 m/s on a flat frictionless railroad track, with no engine pulling the car. It begins to rain. The rain falls straight down and begins to fill the train car.

The speed of the car

A. increases

B. stays the same

C. decreases

Answer 1

Well momentum is constant, so if mass increases velocity must decrease. So as the rain falls in the car, the mass of the car+rain increases so speed must decrease.

Mike