A 8,200-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.

Question

An 8,200-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 at a speed 2 m/s. Compute how much kinetic energy was "lost" in this inelastic collision.

Answer 1

By momentum conservation, the initial truck momentum is conserved as MV = (M + m)v.

Therefore the change of K.E. is

(M + m)v²/2 – MV²/2 = (M + m – (M + m)²/M)v²/2 = –(1 + m/M)mv²/2 < 0.