Question

A stone is dropped freely in the river from a bridge.The stone takes 2 second to touch the water surface in the river.Calculate the height of the bridge from the water level.

Answer 1

Let the height through which the stone drops be H.

Time taken by the stone to touch river (t) = 2 seconds

Initial velocity (u) = 0 m/s

Acceleration due to gravity (a) = 9.8 m/s^2

Now, to find height, we need to use second equation of motion:

$H = u \times t + \frac{1}{2} \times a \times t^2$

$H = 0 \times 2 + \frac{1}{2} \times 9.8 \times 2^2$

$H = 0 + \frac{1}{2} \times 9.8 \times 4$

H = 19.6 m

Hence, the height of the bridge from the river is 19.6 m