Question

a rock is thrown straight upward and it rises to a height of 20m. with what speed was it thrown

Answer 1

$h=\frac{v^2-v_0^2}{2g}=\frac{0^2-v_0^2}{-2g}=\frac{v_0^2}{2g}\to$

$v_0=\sqrt{2gh}=\sqrt{2\cdot9.8\cdot 20}=19.8\ (m/s)$ . Answer