In this question use g=9.8g = 9.8g=9.8 m s−2^{-2}−2
A ball is projected vertically upwards from ground level with speed u u\,u m s−1^{-1}−1.
The ball is modelled as a particle moving freely under gravity.
The ball is more than 20 metres above the ground for a total time of at least 2 seconds.
Using the model, find the set of possible values of uuu.