### Solution:

Concept: Momentum and kinetic energy are frequently preserved in elastic collisions. Assume that two nearby trolleys are moving in the same direction at the same pace. They sprint while maintaining their momentum and bumping into one another. The fact that it has not lost control makes this collision completely elastic.Collisions between objects are governed by the principles of momentum and energy. The total momentum of the entity system is conserved in the event of a collision in an isolated system.

Elastic collisions don't result in any energy loss. Therefore, the kinetic energy following the surface impact would be equal to the energy before to the contact. As a result, just the directions will change; there will be no change in heights.

An elastic collision is one in which there is no net loss of kinetic energy in the system as a result of the collision. Momentum and kinetic energy are frequently conserved quantities in elastic collisions.

Hence, the correct option is 1 .