Question

A rock is dropped from a 300 m –high cliff. How long does it take to fall (a) the first 100 m

and (b) the last 50 m.

Answer 1

(a) The time is

$$t=\sqrt{2h_1/g}=4.5\text{ s}.$$

(b) The total time of flight is

$$T=\sqrt{2H/g}.$$

The time to cover the first 250 m:

$$t_2=\sqrt{2(H-50)/g}.$$

The time to cover the last 50 m:

$$t_3=T-t_2=\sqrt{2H/g}-\sqrt{2(H-50)/g}=0.68\text{ s}.$$