Raketdrift enligt SR

A rocket propels itself rectilinearly by giving portions of its mass a constant (backward) velocity u relative to its instantaneous rest-frame. It continues to do so until it attains a velocity v relative to its initial rest-frame.

Prove that the ratio of the initial to the final rest-mass of the rocket is given by

m_i / m_f = [(c + v)/(c - v)]^q, where q = c/(2u).