A ball is projected vertically upwards from ground level with speed 19.6 m s-1. It is modelled as a particle moving freely under gravity. Use g=9.8 m s−2g=9.8\text{ m s}^{-2}g=9.8 m s−2.
Find the greatest height reached by the ball.
Find the total time for which the ball is at least 14.7 m above the ground.