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A girl is sitting in the middle of a par...

A girl is sitting in the middle of a park of dimension `12 m xx 12 m`. On the left side of it there is a building adjoining the park and on right side of the park, there is a road adjoining the park. A sound is produced on the road by a cracker. Is it possible for the girl to hear the echo of this sound ? Explain your answer.

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For an echo to be heard distincly, the time interval between the original sound and the reflected sound received by the listener should be around `0.1 s`. This distance is obviously, `s = vt = (344 m//s)(0.1 s) = 34.4 m`. The original sound of the cracker falls on girl's ear after travelling a distance of `6 m`. The reflected sound will be received by the girl after sound wave travels `6 m` (from the girl to the building) `+ 6 m` (from building to girl) i.e., `12 m`, which is much less than `34.4 m`, (Fig. 6.40). Hence, no echo is heard.
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