Question

A stone is thrown straight downward with a speed of 20 m/s from the top of a tall building. If the stone strikes the ground 3 s later, how tall is the building? Assume air resistance is negligible.

Answer 1

Given:

$v_0=20\:\rm m/s$

$g=9.8\:\rm m/s^2$

$t=3.0\:\rm s$

The height of a building

$$h=v_0t+gt^2/2\\ =20*3.0+9.8*3.0^2/2=104\:\rm m$$