A railroad car of mass 2.52 104 kg is moving with a speed of 4.06 m/s. It collides and couples with three other coupled railroad cars, each of the same mass as the single car and moving in the same direction with an initial speed of 2.03 m/s.
(a) What is the speed of the four cars after the collision?
(b) How much mechanical energy is lost in the collision?