Question

A woman standing before a cliff claps her hands, 3.6s later she hears the echo. How far away is the cliff? The speed of sound in air at ordinary temperature is 353m/s.

Answer 1

Since we know that the time it takes to the cliff will be half the time it takes for the echo to be heard, the distance is:

$t=\frac{3.6s}{2}\Rightarrow t=1.8s$$d=\frac{353m}{s}\cdot1.8s\Rightarrow d=635.4m$

So, the cliff is 635.4 meters away.