A railroad car of mass M moving at a speed v_{1} collides and couples with two coupled railroad cars, each of the same mass M and moving in the same direction at a speed v_{2}.

(a) What is the speed v_{f} of the three coupled cars after the collision in terms of v_{1} and v_{2}?

(b) How much kinetic energy is lost in the collision? Answer in terms of M, v_{1}, and v_{2}.