Question

a ball is thrown upward with an initial velocity of 20 m/s from the rooftop of a 16 meter tall building and falls freely until it hits the ground. what is the ball's final velocity just before hitting the ground

Answer 1

Find the height the ball will reach above the roof:

$$h=\frac{v^2}{2g}.$$

The velocity at the impact:

$$u=\sqrt{2g(H+h)}=\sqrt{2g\bigg(H+\frac{v^2}{2g}\bigg)}=27\text{ m/s}.$$