A Pie zero meson ( rest-mass energy 135 Mev) is moving with velocity .8c K in the laboratory rest frame when it decays into 2 photons, gamma1 and gamma2. In the pie zero rest frame, gamma1 is emitted forward and gamma2 is emitted backward relative to the pie zero direction of flight. The velocity of gamma2 in the laboratory rest frame is (A) -c k (B) -.2c k (C) .8c k (D) 1.0c k (E) 1.8c k I know that it is either (A) or (D), because it is a photon, must travel at the speed of light in any frame, but I narrowed it down to A, in the rest frame of pie zero, and to D in the laboratory frame, However the correct answer is A in the laboratory rest frame. I am not sure why it is different from my intuition :uhh: . Thank u so much!