Question

A boy, who is standing on a pole of height 14.7 m throws a stone vertically upwards. It moves in a vertical line slightly away from the pole and falls on the ground. Its equation of motion in meters and seconds is $x = 9.8 t − 4.9t^2$Find the time taken for upward and downward motions.

Answer 1

dx/dt = 9.8 - 9.8t 
Set dx/dt, velocity, to zero 
0 = 9.8 - 9.8t 
t = 1 
the time take to reach the ground is 1 sec