Answer:
The velocity just before hitting the ground is 
Explanation:
From the question we are told that
The initial speed is 
The final speed is 
From the equations of motion we have that

Where s is the distance travelled which is the height of the cliff
So making it the subject of the the formula we have that

Where a is the acceleration due to gravity with a value 
So


Now we are told that was through horizontally with a speed of

Which implies that this would be its velocity horizontally through out the motion
Now it final velocity vertically can be mathematically evaluated as

Substituting values


The resultant final velocity is mathematically evaluated as

Substituting values


Using the formula v=f times lambada
then v=the speed of light.
and f=what’s we’re looking for
and lambada=the wavelength.
so then you sub what you have (v and lambada) in the formula.
then multiply the frequency(f) by the given wavelength and then solve for f
kinematic equation
v squared = u squared + 2 a x s
v= sq root (0 + 2 10 x 65)
i thimk
Gravity is the most likely force causing this phenomenon. please leave a thanks