We use kinematic equation of motion,

Here, s is distance traveled, u is the initial velocity, t is time taken and g is acceleration due to gravity.
Given,
.
We take,
because stone has no initial velocity.
Therefore,

Thus, the height of cliff is approximately 61.75 m.
Impuls I is given by:

where

is the change in momentum,

is the average force and t is the time.
Solve the equation for the force F:

Energy should be conserved, so the velocities will be:

Combining both equations:

where
I believe it is true . Somebody correct me if I’m wrong!
C. Scientific theories are based on opinions.
Laws are not based on opinions. They are proven.