What is an elastic collision?

An elastic collision is defined as a type of collision in which the total kinetic energy of the system is conserved before and after the event. This means that the kinetic energy before the collision is equal to the kinetic energy after the collision, with no loss of energy to other forms like heat or deformation. In an elastic collision, not only is kinetic energy conserved, but the momentum of the system is also conserved.

This definition clarifies why the other options do not correctly describe elastic collisions. Kinetic energy being completely lost describes an inelastic collision, where energy is transformed into other forms. The speed of the objects involved is irrelevant to the classification of the collision; elastic collisions can occur at any speed. Furthermore, while many examples of elastic collisions might involve two objects, it's not a requirement; multiple objects can also participate in an elastic collision scenario. Thus, the correct characterization of an elastic collision is that it is one in which no kinetic energy is lost.