# Relativistic inelastic collisions

## Homework Statement

1) Two identical bodies, each with rest mass m(o), approach each other with equal velocities u, collide and stick together in a perfectly inelastic collision. Determine the rest mass of the composite body.

## The Attempt at a Solution

The solution as given in my book is:
Let M(o) be the rest mass of the composite body.
E(initial)=E(final)
[2m(o)c^2]/{[1 - u^2/c^2]^(1/2)} = M(o)c^2
Unlike non relativistic perfectly inelastic collisions, is Total energy conserved in perfectly inelastic relativistic collisions?

## Answers and Replies

Unlike non relativistic perfectly inelastic collisions, is Total energy conserved in perfectly inelastic relativistic collisions?
Total energy and kinetic energy are different things. Kinetic energy is not conserved in inelastic collisions, while total energy is always conserved, regardless of whether or not we take relativistic events into account. (In an inelastic collision, energy is conserved because kinetic energy is transferred into heat/sound, etc.)

Thats cool! Thanx.