A horizontal force of 8.0 Newtons is used to pull a 20 Newton wooden box moving toward the right along a horizontal, wood surface. Calculate the magnitude of the frictional force acting on the box

Arailroad car collides with and sticks to an identical railroad car that is initially at rest. after the collision, the total kinetic energy of the two cars is a) the same as before. b) half as much as before. c) one third as much as before. d) one fourth as much as before. e) twice as much as before.