25 ! when is a collision considered inelastic?

When Kinetic energy is not conserved.

Explanation:

When collision occurs, a body transfer its velocity to another. But sometimes the kinetic energy K= 1/2(mv²) is not conserved, in that case collision is termed as Inelastic collision.

This happens due to action of internal friction. The lost kinetic energy is transferred into some different energy such as thermal energy or sound energy.

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real, smaller and upside-down.   so the answer should be b.