A child drops a stone of 1 kg from the top of a tower. Find its kinetic energy, 5 s after it starts falling. (Take, g = 10${{ms}^{-2}}$)

1 Initial velocity, u = 0, time, t — 5 s

Acceleration due to gravity, g — 10 ${{ms}^{-2}}$

As from equation of motion,

v = u + gt [for downward motion]

=> v =0+10x5 => t> = 50${{ms}^{-1}}$

.’. Kinetic energy of the stone is given by 1/2 m${{v}^{2}}$ = 1/2 x 1 x 50 x 50 = 1250 J