WAEC Physics 2015 Paper

Concept:When a body falls freely, its potential energy is completely converted into kinetic energy just before striking the ground.Explanation:The body starts at height $h = 10 \, \text{m}$ with mass $m = 1000 \, \text{kg}$ and $g = 10 \, \text{m/s}^2$.Its initial potential energy is:$$E_p = mgh = 1000 \times 10 \times 10$$$$E_p = 100000 \, \text{J}$$By the law of conservation of energy, the kinetic energy just before impact equals the initial potential energy.Therefore:$$E_k = E_p = 100000 \, \text{J} = 10^5 \, \text{J}$$Answer:The kinetic energy is $10^5 \, \text{J}$.Correct option: D. $10^5 \, \text{J}$