2. A small stone is projected vertically upwards from a point \(O\) with a speed of \(19.6 \mathrm {~ms} ^ { - 1 }\). Modelling the stone as a particle moving freely under gravity,
- find the greatest height above \(O\) reached by the stone,
- find the length of time for which the stone is more than 14.7 m above \(O\).