Question

A boy hears an echo of his own voice from a distant hill after 1s.the distance of the hill from the boy is 175m .what is the speed of sound in air

Answer 1

You assume that the speed of sound is 340 m/s? And the boy hear the echo of his clap after 0.8 seconds?

Well, if so, then you only need to divide the time by 2 and multiply it by the speed of sound and you have your answer.

Answer 2

Given ,

Distance (S) of the hill from the boy is 175 m

Time (t) = 1 sec

$\star$ The total distance travelled by sound in going and coming back is 2S , therefore

$\large \sf \fbox{ \fbox{2S = v × t }}$

$\implies \sf 2 \times 175 = v \times 1 \\ \\ \implies \sf v = 350 \: \: m/s$

$\therefore$The velocity of sound in air is 350 m/s