Question

A ball is thrown vertically upwards from the ground . it crosses a point at a height of 25 m twice at an interval of 4 s.find velocity with which the ball was thrown

Answer 1

pay attention to the picture and the following equations
V=-gt+v
put 2 in the equation and v=-20
\[v^2-V^2(0)=-2g \Delta x\]
so V(0)=30 m/s