Question

A rock is dropped from a 164-m-high cliff. How long does it take to fall (a) the first 82.0 m and (b) the second 82.0 m

Answer 1

Answer:

Explanation:

Given

Rock is dropped from a height of $h=164\ m$

Rock is drooped so initial velocity is zero i.e. $u=0$

Time taken to fall $82\ m$ is given by

$y=ut+\frac{1}{2}at^2$

where  

y=displacement

u=initial velocity

a=acceleration

t=time

$164=0+\frac{1}{2}gt^2$

$t=\sqrt{\frac{2\times 82}{9.8}}$

$t=4.09\ s$

Now time taken to fall another 82 m

We can calculate this time by first calculating time taken to cover 82+82 m and then subtracting the time taken to cover 82 m

$t_2=\sqrt{\frac{2\times 164}{9.8}}$

$t_2=5.78\ s$

time taken $=t_2-t=5.78-4.09=1.69\ s$