Pi meson decay*
A neutral pi meson (π0), rest mass 135 MeV, decays symmetrically into two photons while moving at high speed. The energy of each photon in the laboratory system is 100 MeV.
(a) Find the meson's speed V as a ratio V/c.
(b) Find the angle θ in the laboratory system between the momentum of each photon and the initial line of motion.