JAMB Physics 2011 Paper

Concept:For vertical motion under gravity, acceleration is the same for all masses, so both balls have identical motion when launched with the same initial velocity.Explanation:Take upward as positive and use $g = 10\ \mathrm{m\,s}^{-2}$.The displacement after time $t$ is given by:$$s = ut - \frac{1}{2}gt^{2}$$Here, $u = 100\ \mathrm{m\,s}^{-1}$ and $t = 1\ \mathrm{s}$.So:$$s = 100(1) - \frac{1}{2}(10)(1)^{2}$$$$s = 100 - 5 = 95\ \mathrm{m}$$This distance does not depend on mass.The 5 g ball and the 50 kg ball are acted on by the same gravitational acceleration.Therefore, after one second, both balls are at the same height above the point of throw.Answer:Both balls are at the same position, $95\ \mathrm{m}$ from the point of throw, so none of the provided options is correct.