Griffiths Introduction to Elementary Particles · Problem 3.20
Symmetries — David J. Griffiths
Physics — QFT · cm-frame-kinematics
Problem
(a) A particle traveling at speed v approaches an identical particle at rest. What is the speed of each particle in the CM frame? (*Classically*, of course, it would just be v/2. Why *isn't* this true relativistically?)
(b) Use your result in part (a) to compute the kinetic energy of each particle in the CM frame, and thus rederive equation (3.53).