If we throw a body upwards with velocity of 4 m/s what height its kinetic energy reduces to half of the initial value ? Take  $g=10m/s^2$

 Initial energy

$=\frac{1}{2}{\mathrm{mv}}^2=\frac{1}{2}\mathrm{m}(4{)}^2=8\mathrm{m}$

Let at height i, the kinetic energy reduces to half, i.e , it becomes 4 m. It is also equal to potential energy. Hence
$$\begin{gathered} \mathrm{mgh}=4\mathrm{m} \\ \mathrm{or} \mathrm{h}=\frac{4}{\mathrm{g}}=\frac{4}{10}=0\cdot 4\mathrm{m} \end{gathered}$$