1. The problem statement, all variables and given/known data A neutral pion may decay into two photons. A particular pion is traveling along the x axis when it decays into two photos, the first going directly along the +x axis, the second going directly back along the -x axis. The energy of the photons is measured and it is found that E1 is n times more energetic than E2. Find the velocity u of the pion. 2. Relevant equations 1) relativistic momentum = gamma *m*u where u is velocity, m is mass 2) momentum of a photon is h/wavelength = h*frequency/c (I'm denoting frequency by nu). 3. The attempt at a solution I tried to do this using conservation of momentum. I'd like to know if my solution is correct. Pi = Pf (via conservation of momentum for isolated system) so gamma*m*u = h*nu1/c - h*nu2/c (the minus sign accounts for the fact that the photons move in opposite directions along the x axis) but as given above, E1 = n*E2, so gamma*m*u = h*nu2 (n - 1)/c Then I solved for u using algebra (I didn't forget about the u in gamma, I squared everything and solved for u afterwards). Can that be right? Or am I thinking way too simplistically here?