Question:

Imagine that a reactor converts all given mass into energy and that it operates at a power level of 10⁹W. The mass of the fuel consumed per hour in the reactor will be (velocity of light, c is 3×10⁸m/s)

0.96gm

4×10⁻⁶gm

6.6×10⁻⁹gm

0.8gm

Energy converted in one hour =p×t=10⁹×3600sec=36×10¹¹J
Mass of fuel consumed in one hour is
M=E/c²
M=36×10¹¹/(3×10⁸)²
M=4×10⁻⁶kg=4×10⁻⁶gm