In which type of collision is kinetic energy lost?

In an inelastic collision, some portion of the kinetic energy of the system is transformed into other forms of energy, such as heat, sound, or internal energy, during the collision process. This is a defining characteristic of inelastic collisions, where the objects involved may stick together or deform, indicating that kinetic energy is not conserved. While momentum is conserved in both elastic and inelastic collisions, kinetic energy conservation occurs only in elastic collisions.

In the case of perfect inelastic collisions, the two colliding objects stick together after impact, resulting in a significant loss of kinetic energy. However, since "inelastic collision" encompasses both cases where energy is lost and situations where the objects may still separate (but are still not conserving kinetic energy), it is appropriately answered as inelastic collision since it broadly indicates situations where kinetic energy is lost.

The terms in the other options refer to scenarios where kinetic energy is conserved or altered in predictable ways that do not fit the definition of kinetic energy loss. Therefore, the classification of inelastic collisions captures the essence of kinetic energy loss correctly.