work energy power Questions

A ball is thrown vertically downwards from a height of $20\text{m}$ with an initial velocity $v_0$. It collides with the ground, loses $50$ percent of its energy in collision and rebounds to the same height. The initial velocity $v_0$ is: (Take $g=10{\text{m s}}^{-2}$)

The heart of a man pumps $5\text{litres}$ of blood through the arteries per minute at a pressure of $150\text{mm}$ of mercury. If the density of mercury be $13.6\times 10^3{\text{kg/m}}^3$ and $g=10{\text{m s}}^2$ then the power of heart in watt is: