## Question

In fusion of hydrogen isotopes into helium the decrease in mass is about 0.65%. Calculate the energy obtainable when 1.0 gram of hydrogen is used. [ c = 3.0 x 10^{8} m/s]

### Answer

**Data:**

Mass defect, m = (0.65 / 100) x 1.0g

but 1.0 g = (1/1000) kg = 0.001 kg

Hence, m = (0.65/100) x 0.001 kg = 6.5 x 10^{6} kg

The energy obtained, E = mc^{2} = (6.5 x 10^{6}) x (3.0 x 10^{8})^{2} = 5.85 x 10^{11} J

E = 5.85 x 10^{11} Joules