Question

a stone is projected vertically up from the top of a tower 73.5m with velocity 24.5 m/s . find the time taken by the stone to reach the foot of the tower?​

Answer 1

Hi.

The height of tower is 73.5m.

The stone is thrown upwards with velocity 24.5m/s. It will:

A) Go up, then stop, then start down, reach the top of building. Then

B) It will reach the foot of tower.

Time for part A:

$t=\frac{2u_y}{g}$

Where uy= Initial velocity

$t=\frac{2*24.5}{9.8}\\t=5s$

Now for part B, initial velocity is -24.5, g=9.8m/s² and s=73.5m

$s=ut+\frac{at^2}{2}\\73.5=-24.5-\frac{gt^2}{2}\\49=gt^2/2\\\frac{98}{9.8}=t^2\\t=\sqrt{10}sec$

Total=5+√10 seconds=8.16seconds