Bruger:John.St/sandkasse

${\begin{aligned}E_{r}^{2}-|{\vec {p}}\,|^{2}c^{2}&=m_{0}^{2}c^{4}\\E_{r}^{2}=(m_{0}c^{2})^{2}+(pc)^{2}\\E_{r}^{2}-(pc)^{2}&=(m_{0}c^{2})^{2}\\E_{r}={\sqrt {(m_{0}c^{2})^{2}+(pc)^{2}}}\,\!\end{aligned}}$

${\begin{aligned}E_{r}^{2}-|{\vec {p}}\,|^{2}c^{2}&=m_{0}^{2}v^{4}\\E_{r}^{2}=(m_{0}v^{2})^{2}+(pc)^{2}\\E_{r}^{2}-(pc)^{2}&=(m_{0}v^{2})^{2}\\E_{r}={\sqrt {(m_{0}v^{2})^{2}+(pc)^{2}}}\,\!\end{aligned}}$