# I How can I calculate the energy of a body of mass?

Tags:
1. Nov 1, 2018

### DLeuPel

Since E = mc2 the if I know the mass and the energy I can figure out the constant c2, but how do I know how much energy does the body have ? How do I calculate it ?

2. Nov 1, 2018

### PeroK

Normally you would measure its rest mass, $m$, and multiply by $c^2$. That would give you the rest energy, $E$.

These days $c$ is defined to have a certain value. So, you don't calculate it from other quantities, or from experiment.

3. Nov 1, 2018

thanks