Should be fairly simple, but I'm not so great with physics. Here's a few I'm having trouble with... 1. Under what circumstances (if any) is no work done on a moving object even though a net force acts upon it? 2. What happens to the momentum of a car when it stops? 3. When the kinetic energy of an object is doubled, what happens to its momentum? 4. A railway car is at rest on a frictionless track. A man at one end of the car walks to the other end. (a) Does the car move while he is walking? ( If so, in which direction? © What happens when the man comes to a stop?