Question

A ball is thrown vertically upwards from the top of a tower with a speed of 100 m/s. It strikes the pond near the base of the tower after 25 seconds. The height of the tower is___.

• A. 500 m
• B. 125 m
• C. 625 m
• D. 425 m

Answer 1

The correct option is C 625 m

The ball would reach at top of tower at time,
$T=\frac{2u}{g}=2\times \frac{100}{10}=20s$.
that means to cover the height it take 5 seconds.
velocity at the top of tower on returning would be:
$v=100g\times 20=-100m/s$ downwards.
Therefore to cover h distance from 2nd eqn. of motion :
$h=100\times 5+0.5\times g\times 25$
= 500 + 125
= 625 meter.