A rock is dropped downward from the top of a cliff. If the rock hits the ground after 2.0 s, what's the height of the cliff?

Answer: 19.6 m

Explanation:

A rock is dropped from the cliff. It means its initial velocity, u = 0 m/s

It free falls under gravity.

Using the second equation of motion:

s = u t + 0.5 a t²

s = height of cliff

u = initial velocity = 0

t = time of fall = 2.0 s

a = g = acceleration due to gravity = 9.8 m/s²

⇒ s = 0 + 0.5 * 9.8 m/s² * (2.0 s) ² = 19.6 m