A particle with mass m has speed c!2 relative to inertial
Chapter 37, Problem 81(choose chapter or problem)
A particle with mass m has speed c!2 relative to inertial frame S. The particle collides with an identical particle at rest relative to frame S. Relative to S, what is the speed of a frame S' in which the total momentum of these particles is zero? This frame is called the center of momentum frame.
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