A child pulls a sled by a rope across the snow. The sled accelerates at 1.5 m/s/s. The child applies a force of 20 N to the sled, which has a mass of 2 kg, at an angle of 10 degrees above the horizontal. What is the coefficient of friction between the sled and the ground?

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.