How much less, and what becomes of this energy?

Question

Consider the elastic collision between two freight cars in figure 3.9. The momentum before and after the Collision is the same. The KE, however, is less after the Collision than before. How much less, and what becomes of this energy?

Answer 1

When the one car hits the other car some energy is transferred to the second car.

The total momentum of the two cars is the same. This is the meaning of an elastic collision.

However the momentum of the first car is reduced by the amount that was transferred to the second car.

since no mass was lost this resulted in a loss of velocity.

The total kinetic energy would also be conserved but the first car would lose the energy that was transferred to the second car. The only time kinetic energy would be lost would be if the collision was not elastic and some energy was lost.