Question

A body is projected upward with a velocity of 30m/s. Find the time when the velocity will be 5m/s

Answer 1

Under the influence of gravity, the object decelerates at the rate of 9.8 m/s². So, the time is

$$t=\frac{v_2-v_1}{g}=\frac{5-30}{-9.8}=2.55\text{ s}.$$