You hold a metal block of mass 40 kg above your head at a height of 2 m how much work is done bu gravity if you let the block fall to 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.