Question

If you drop a rock off a cliff and it hits the ground 4 seconds later, how tall is that cliff?

Answer 1

We can find the height of the cliff from the kinematic equation:

$$y=\dfrac{1}{2}gt^2=\dfrac{1}{2}\cdot 9.8\ \dfrac{m}{s^2}\cdot (4\ s)^2=78.4\ m.$$

Answer:

$y=78.4\ m.$