a box of mass 15kg placed on a horizontal floor is pulled by a horizontal force. What will work done by the force if the coefficient of sliding friction between the box and surface of the floor is 0.3 and body moved at unit distance

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.