Answer to Question #87965 in Mechanics | Relativity for Maaloof

Question

A worker on a roof, 20.8 m above the ground, wants to drop a brick onto the back of a moving truck. The
truck is moving at a constant velocity of 5.0 m/s alongside the building. The back of the truck is 1.2 m
above the ground. How far from the point of impact must the truck be, the instant the brick is dropped, so
that the brick will land on the back of the truck?

Answer 1

Time of flight:

$$t= \sqrt{\frac{2(H-h)}{g}}= \sqrt{\frac{2(20.8-1.2)}{9.8}}=2 s$$

Needed distance is

$$s=vt=(5)(2)=10m.$$