Question

A ball thrown vertically downward from the top of a building living the throwers hand with the velocity of 10 m per second. If the ball was through from a point 40 m above the ground how long does it take to strike the ground?

Answer 1

$s=vt+\frac{gt^2}2,$

$t=\frac{\sqrt{v^2+2gs}-v}{g},$

$t=2~s.$