A small stone is projected vertically upwards with speed \(20 \mathrm {~ms} ^ { - 1 }\) from a point \(O\) which is 5 m above horizontal ground. The stone is modelled as a particle moving freely under gravity.
Find
the speed of the stone at the instant when it is 2 m above the ground,
the total time between the instant when the stone is projected from \(O\) and the instant when it first strikes the ground.