Question

A stone released into the

Answer 1

Answer:

h = 78.4  m

Explanation:

Given that,

A stone takes 4s for the stone to touch  the river's water surface.

We need to find the height of  the bridge from the water  level​.

Let the height be h. We can use the second equation of motion to find h. So,

$h=ut+\dfrac{1}{2}gt^2\\\\ \because u=0\\\\So,\\\\h=\dfrac{1}{2}\times 9.8\times 4^2\\\\h=78.4\ m$

So, the height of the bridge from the water level is 78.4  m.