Question

A stone lying at the edge of the road falls down into the river flowing below the road. If the stone takes 2 seconds to reach the river, then find speed with which the stone strikes the water surface in the river

Answer 1

Let's say that the vertical distance of river from road is h. Time taken for the stone to reach river is 2 seconds.
Using the below equation and putting u=0 (Because stone was at rest initially)
$v ^{2} - {u}^{2} = 2gh$
We get,
$v = \sqrt{2gh}$
Where g is the acceleration due to gravity.
And using
h = 1/2gt²
we get h=20m
And putting value of h in above equation we get v=20m/s

Answer 2

Of u want simplest answer then use brain let velocity be v then t=u/g.get v=20m/s