申論題

8. A relativistic particle of mass M with total energy E decays into a lighter particle of mass m together with some other undetected particles. The particle m also decays afterwards. The proper lifetime of particle M is measured to be T and the proper lifetime of particle m is t. If half of the kinetic energy of particle M has been transmitted to particle m during this process, what are the flight distances of the particle M and of the particle m, from an observer at rest?