I know the standard formula, but how would I use it in this context?

Question

The Sun generates energy at the rate of about 3.9 × 10²⁶ W. Use Einstein’s equation to verify that the Sun loses mass at the rate of about 4 million tonnes per second.

Answer 1

Einstein 's mass-energy equation is E = mc². If the sun generates 3.9 x 10²⁶ Watts, this is equal to 3.9 x 10²⁶ J/s. This is substituted for E in the above equation which can be solved for m knowing c is approximately 3x10⁸ m/s. Doing the math gives m = 4.3 x 10⁹ kg/s or 4.3 x 10⁶ metric tons (or tonnes) per second.