JAMB Physics 2011 Paper

Concept:The falling hammer converts gravitational potential energy into kinetic energy, so just before impact, $KE = PE$.Explanation:At the top of the roof, the hammer is at rest, so its kinetic energy is zero.Its potential energy is given by $PE = mgh$.Substitute the values: $m = 1.5\,kg$, $g = 10\,ms^{-2}$, and $h = 20.0\,m$.$PE = 1.5 \times 10 \times 20$$PE = 300\,J$By conservation of mechanical energy, the kinetic energy just before hitting the ground equals this potential energy.Therefore, $KE = 300\,J$.Answer:C. $300\,J$