Question

A body of mass 10 kg is moving with a velocity 20 m $s^{-1}$. If the mass of the body is doubled and its velocity is halved, find:(i) the initial kinetic energy, and (ii) the final kinetic energy.

Answer 1

(i) Initial kinetic energy $=\frac{1}{2}m{v}^2=\frac{1}{2}\times 10\times {20}^2=2000J$

(ii) If mass is doubled and velocity halved, final kinetic energy $=\frac{1}{2}\times 2m\times {\left(\frac{v}{2}\right)}^2=\frac{1}{2}\times 20\times {10}^2=1000J$