Question

atleast how far should somebody stand from a surface that reflects sound so that she can hear an echo when she claps her hands (take velocity of sound = 340m/s)

Answer 1

Here's your answer,

We know that,

The speed of sound in air = 340 m/s
Minimum time required to hear an echo= 0.1 s
The distance travelled by the sound in 0.1 s = speed× time
= 340m/s × 0.1 s
= 34m
As the sound travels twice between the source and the reflecting surface before an echo is heard, the minimum distance required to hear an echo =
= 34/2 m
= 17 m

Thus the minimum distance required for occurrence of an echo is 17 m.

Hope this helps!!!