Question

A person is standing between two cliffs. He claps and hears two echoes, one after 3 seconds and the other after 5 seconds. If the velocity of sound in air = 336$\frac{m}{s}$. Find the separation between the two cliffs.

• A. 1344 m
• B. 2688 m
• C. 772 m
• D. 862 m

Answer 1

The correct option is A

1344 m

When we hear an echo, distance travelled by the sound wave is two times the actual distance between the cliffs. Hence, time taken by sound to reach the wall is half of the time in which the echo is heard by the person.
Now, the total time for first and second echo is = 3sec + 5 sec.
Thus, time taken by the sound to reach cliff = $\frac{8sec}{2}$ = 4 sec.
Distance between the cliff = Time taken by sound to reach the cliff $\times$ Velocity of sound
Distance between the cliff =4 $\times$ 336 m.
Distance between the cliff = 1344 m.