# Homework Help: Calculation of momentum of relativistic particles

1. Apr 20, 2012

### physicsblr

1. The problem statement, all variables and given/known data
A particle of mass M decays at rest into a massless particle and another particle of mass m. The magnitude of the momentum of each of these relativistic particles is:

2. Relevant equations

E = γmc2; p=γmv

3. The attempt at a solution
Pf-Pi = 0; but the particle is at rest, so pi = 0; and the momentum of massless particle = 0;

2. Apr 20, 2012

### George Jones

Staff Emeritus
This isn't correct. Look in your notes and/or text for the relationship between energy and momentum for a massless particle.

3. Apr 20, 2012

### physicsblr

No, I tried the relation E2 = m2c4+p2c2 also, am not getting right answer. There are no explanations of this in my text graduation text books. These are pg level questions.

I did substitute E2 = M2c4 (initial energy) and onto r.h.s, p2c2+m2c4+p2c2 - p2c2 is the kinetic energy of the massless particle and m2c4+p2c2 for the particle of mass m.

Please give a solution if possible, am taking so much time to google n check. I am already running out of time for my entrance exam next week.