A stone is tossed off a cliff and into a crevasse from a starting height of 20 meters and an initial velocity of 15 meters per second. How long will it take the stone to hit the floor of the crevasse?

$$\begin{gathered} h=\frac{1}{2}a{t}^2+vt+s \\ a=–9.8, v=15, s=20 \\ h=\frac{1}{2}\left(–9.8\right)t^2+15t+20 \\ h=–4.9t^2+15t+20 \\ x=\frac{–15\pm \sqrt{{\left(15\right)}^2–4\left(–4.9\right)\left(20\right)}}{2\left(–4.9\right)} \\ x=\cancel{–1.004,} 4.065 \\ x=4.065 \end{gathered}$$

It will take 4.065 seconds for the stone to hit the bottom of the crevasse.