|Jan8-13, 11:57 AM||#1|
Velocity of the centre of mass of two photons
1. The problem statement, all variables and given/known data
Find the velocity of the centre of mass of two photons with different energies (they happen to be approaching).
2. Relevant equations
E = hf p(photon) = E/C E=gamma(mc^2)
3. The attempt at a solution
I have calculated the energy of the two photons in the centre of mass frame (using conservation of 4- momentum) and also the momentum of the centre of mass. However I have no idea how to get a velocity out of this.
|Jan8-13, 12:19 PM||#2|
How does the momentum of the center of mass look like in our lab frame?
If you know energy and momentum of that frame, you can calculate the corresponding velocity - it is like a particle at rest in this frame.
|Jan8-13, 02:37 PM||#3|
Welcome to PF, Fek!
From the definitions of 4-momentum and 4-velocity:
Furthermore, for a photon we have:
Can you deduce v from this?
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