physics 101 lost energy

Question

A 8,300-kg truck runs into the rear of a 1,000-kg car that was stationary. The truck and car are locked together after the collision and move with speed 2 m/s. Compute how much kinetic energy was "lost" in this inelastic collision.

Answer 1

By conservation of momentum, MV = (M + m)v so the truck's speed before collision was V = (1 + m/M)v.

The change in k.e. is MV²/2 – (M + m)v²/2.