Question

A boy standing in front of a wall at a distance 17 m produces 10 claps per second. He notices that the sound of his clapping coincides with the echo. Echo is heard only once when clapping is stopped. Calculate the speed of sound.

Answer 1

Let d be the distance of the wall from the boy.
To hear the echo, the sound has to travel a distance.
2d = 2 × 17 = 34 m.
Since 10 claps are produced in one second, therefore each clap is produced after 1/10 s which is equal to the time taken for the echo to be heard (according to the question), i.e., t = 1/10 s = 0.1 s.
Now speed of sound V = `"Distance travelled"/"Time taken"=34/0.1`
= 340 ms⁻¹.