Question

You throw a stone horizontally at a speed of 5.0 m/s from the top of a cliff that is 78.4 m high. How long does is take the stone to reach the bottom of the cliff?

Answer 1

$$y=\dfrac{1}{2}gt^2,$$ $$t=\sqrt{\dfrac{2y}{g}}=\sqrt{\dfrac{2\cdot78.4\ m}{9.8\ \dfrac{m}{s^2}}}=4.0\ s.$$