A body moving with velocity v, which absorbs … in the process, has, as a consequence its … Thus the body has the same energy as … body takes up an amount of energy E_0, … not a constant, but varies according to the … even be regarded as a measure of its … we see that the term mc^2 … is nothing else than the energy possessed by … [footnote: "As judged from a coordinate system moving with the body"] before it absorbed the energy E_0.
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