2 A small ball is projected vertically downwards with speed \(5 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) from a point \(A\) at a height of 7.2 m above horizontal ground. The ball hits the ground with speed \(V \mathrm {~m} \mathrm {~s} ^ { - 1 }\) and rebounds vertically upwards with speed \(\frac { 1 } { 2 } V \mathrm {~m} \mathrm {~s} ^ { - 1 }\). The highest point the ball reaches after rebounding is \(B\). Find \(V\) and hence find the total time taken for the ball to reach the ground from \(A\) and rebound to \(B\).