That's "just" special relativity. I would suggest to see it exposed in current textbooks. Spoiler: E=m_rest c2 + E_kinetic unless you redefine the mass as a fu

That's "just" special relativity. I would suggest to see it exposed in current textbooks. Spoiler: E=m_rest c2 + E_kinetic unless you redefine the mass as a function of velocity. Something that people used to do a century ago but is unusual to it nowadays