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The total energy of a body of mass m is given by

E = γmc2

where total energy = kinetic energy + rest energy


E = KE + E0

When a body is at rest γ = 1, KE = 0 and the rest energy E0 is given by

E0 = mc2

The rest energy includes all forms of energy internal to the system.

The kinetic energy of a body of mass m is

KE = γmc2 - mc2

If the speed of the object is not too large, this reduces too the usual expression

KE = ½mv2 ( v << c )

Using the expression p=γmv, the total energy of a body can be written as:

E2 = m2c4 + p2c2

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