Question

Two balls are projected simultaneously with same speed from top of a tower, one vertically upward and the other downward. If they reach the ground in 9 s and 4 s respectively, then find the height of tower.

Answer 1

Explanation:

For a body projected upwards

total time=9s

time taken to reach the point of projection =5s

time taken to reach the maximum height =5/2s

final velocity=0

acceleration =-10m/s

then initial velocity (u) =25m/s

for a ball moving downwards

initial velocity =25m/s

time =4s

acceleration =10m/s

$h = ut + \frac{1}{2} g {t}^{2} \\ h = 25 \times 4 + \frac{1}{2} \times 10 \times 4 \times 4 \\ h = 100 + 80 = 180m$