WAEC Physics 2015 Paper

Concept:Newton's law of universal gravitation states that the attractive force between two masses is proportional to the product of their masses and inversely proportional to the square of the distance between them.Explanation:The formula is $F = \frac{G M_1 M_2}{r^2}$, where $G = 6.7 \times 10^{-11} \, \mathrm{N\,m^2\,kg^{-2}}$.Here, $M_1 = 6.0 \times 10^{24} \, \mathrm{kg}$ and $M_2 = 7.0 \times 10^{22} \, \mathrm{kg}$.The distance between them is $r = 4.0 \times 10^{8} \, \mathrm{m}$.Substitute the values into the equation:$$F = \frac{6.7 \times 10^{-11} \times 6.0 \times 10^{24} \times 7.0 \times 10^{22}}{(4.0 \times 10^{8})^2}$$$$F = \frac{2.814 \times 10^{37}}{1.6 \times 10^{17}}$$$$F = 1.8 \times 10^{20} \, \mathrm{N}$$Answer:The force of attraction between the Earth and the Moon is $1.8 \times 10^{20} \, \mathrm{N}$.Therefore, the correct option is D.