A stone is released from rest and allowed to fall freely under gravity. After it has fallen a vertical distance of 20\,m, its velocity has to be found.
(i) The quantities known are u=0, s=20m and g=9.8ms−2. Out of the three standard kinematic relations for uniformly accelerated motion, name the one that can give the velocity directly without first calculating the time, and explain in one or two sentences why it is the most efficient choice.
(ii) Rewrite the chosen equation so that the velocity v is the subject.
(iii) Give any two other distinct situations of free fall (you may change the numerical data) where the same equation would still be the most convenient starting point to obtain the required result.