1. The problem statement, all variables and given/known data A K0 particle is unstable and has a mass of 8.87x10-28 kg. It can decay into π+ and π- particles, each of mass 2.49x10-28 kg. Suppose that a K0 is moving in the +x direction and decays by this process, with the π+ moving off at 0.9c and the π- moving off at 0.8c. a) What was the speed of the K0 before the decay? b) In what directions do each of the π particles move after the decay? 2. Relevant equations Pinitial=P1+P2 3. The attempt at a solution I assume that the momentum is conserved thus Pinital=P1+P2. I also know that P=gamma*mass*velocity So with that information, I can solve for the momentum of the two particles. P1+P2=2.12*10^-19 Now I know my total momentum, thus I isolate for velocity. HOWEVER, the original mass of the kaon is 8.87*10^-28, but the masses of the two particles do not add up to the total mass, where did the lost mass go? Energy? If so, how do I solve th problem? Also, for part b) do I just say, they are in opposite directions?