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Question
(i) A man stands at a distance of 68 m from a cliff and fires a gun. After what time interval will he hear the echo, if the speed of sound in air is 340 ms−1?
(ii) If the man had been standing at a distance of 12 m from the cliff would he have heard a clear echo?
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Solution
(i) d = 68 m, v = 340 ms−1.
∴ Time taken = `"total distance"/"speed"=68/340=1/5`
= 0.2 s (second)
So echo is heard after 2t i.e.
0.2 × 2 = 0.4 sec.
(ii) If man had been standing at a distance 12 m then
t = `"2d"/"v"=(2xx12)/340=24/340` = 0.07 sec.
which is less than 0.1 sec.
Hence, man can not hear a clear echo.
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