A boy standing in front of a wall at a distance of 85 m produces 2 claps per second. He notices that the sound of his clapping coincides with the echo. The echo is heard only once when clapping is stopped. Calculate the speed of sound.

340 m s^{- 1}

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140 m s^{- 1}

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600 m s^{- 1}

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540 m s^{- 1}

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Solution

The correct option is A $340 m s^{- 1}$
Given, distance of wall from the boy, $d = 85 m$ .
To hear the echo, sound has to travel a distance $= 2 d = 2 \times 85 = 170 m$
Since 2 claps are produced in one second, each clap is produced after $\frac{1}{2} s$ which is equal to the time taken for the echo to be heard.
That is, $t = \frac{1}{2} = 0.5 s$
Speed of sound, $v = \frac{t o t a l d i s t a n c e t r a v e l l e d}{t o t a l t i m e} = \frac{170}{0.5} = 340 m s^{- 1}$

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