WAEC Physics 2011 Paper

Concept:Nuclear energy released equals the mass defect multiplied by the square of the speed of light.Explanation:Use Einstein’s mass-energy relation, $E = \Delta m c^2$.The mass defect is $\Delta m = 2.0 \times 10^{-27}\ \mathrm{kg}$.The intended value of the speed of light, consistent with the options, is $c = 3.0 \times 10^8\ \mathrm{m\,s^{-1}}$.(Using the given $2.0 \times 10^8\ \mathrm{m\,s^{-1}}$ would give $8.0 \times 10^{-11}\ \mathrm{J}$, which is not listed.)Substitute into the equation:$E = (2.0 \times 10^{-27}) \times (3.0 \times 10^8)^2$$E = (2.0 \times 10^{-27}) \times (9.0 \times 10^{16})$$E = 1.8 \times 10^{-10}\ \mathrm{J}$.Answer:The amount of energy released is $1.8 \times 10^{-10}\ \mathrm{J}$.Therefore, the correct option is A.