Why don't inelastic collisions conserve energy?
- The classic is a bug splatting against the windshield (windscreen) of a car. Work is done on that bug, changing its shape, so some kinetic energy is lost.
- When 2 cars collide, energy goes toward changing the shape of both cars' bodywork.
In the first example, that is a fully inelastic collision because the 2 masses remain stuck together. In the second example, if the 2 cars bounce off separately, that was an inelastic collision, but not fully inelastic.
Momentum is conserved in both cases, but not energy.
I hope this helps,