2 A stone is released from rest and falls freely under gravity. Find
- the speed of the stone after 2 s ,
- the time taken for the stone to fall a distance of 45 m from its initial position,
- the distance fallen by the stone from the instant when its speed is \(30 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) to the instant when its speed is \(40 \mathrm {~m} \mathrm {~s} ^ { - 1 }\).