A ball is thrown vertically downwards from a height of $20 \mathrm{~m}$ with an initial velocity $\mathrm{V}_{0}$. 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 $g=10 \mathrm{~ms}^{-2}$ ) (1) $10 \mathrm{~ms}^{-1}$ (2) $14 \mathrm{~ms}^{-1}$ (3) $20 \mathrm{~ms}^{-1}$ (4) $28 \mathrm{~ms}^{-1}$