Ariver current has a velocity of 5km/h relative to the shore, and a boat moves in the same direction as the current at 5km/h relative to the river. how can the velocity of the bot relative to the shore b calculated?

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.