# Special Relativity Decay

1. May 19, 2010

### bon

1. The problem statement, all variables and given/known data

A K meson has a total energy of 890 MeV in a laboratory where it decays along
its line of ﬂight into two π mesons. At what speed is the K meson travelling in the
laboratory frame prior to the decay? What are the velocities and energies of the π
mesons in the laboratory frame?

2. Relevant equations

3. The attempt at a solution

Would the two pi mesons be moving together? If so, I know how to solve the problem...

If they would be - why do they? If not, why not?
Thanks

2. May 19, 2010

### Andrew Mason

What are the rest masses of the K meson and $\pi$ mesons? You will need that information to solve this problem.

What is conserved here? Can it be conserved if the $\pi$ mesons are moving at the same speed as the K meson was? If not, can they change speed and still be moving together ?

AM