A railroad car with a mass of 5.010 kg collides with a stationary railroad car of equal mass. After the collision, the two cars lock together and move off at 4.0 m/s 

a. Before the collision, the first railroad car was moving at 8.0 m/s. What was its momentum? 

b. What was the total momentum of the two cars after the collision? 

c. What were the kinetic energies of the two cars before and after the collision? 

d. Account for the loss of kinetic energy.