Question

A man stands between two walls. He clapped his hands once and hears two echoes – one after 0.500 s and the other 0.300 s after the first. If the speed of sound in air is 330 ms^-1, what is the distance between the two walls?

Answer

The first echo comes from the sound that travels to the nearer wall and reflects back.

The distance travelled by the sound is

Since the sound travels twice the distance between the man and the nearer wall,

The second echo comes from the sound that travels to the farther wall and reflects back.

We can calculate the distance travelled by the sound and the distance between the man and the farther wall.

Hence, the distance between the two walls can be found.