Answer to Question #119735 in Physics for Sky

Question

Why would KE of combined carts after a collision be less than the KE of the carts before the collision?

Answer 1

The KE of combined carts after a collision will be less than the KE of the carts before the collision because according to the energy conservation principle, some energy will be lost to mechanical work required to deform or destroy the carts, heat of the bent or crashed parts, and some work done against friction is the carts slip on the road:

$$KE_1=KE_2+W_\text{destruction}+Q_\text{destruction}+W_\text{friction}\\ KE_2<KE_1$$