An echo returned in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m/s.

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• A 520 m
• B 515 m
• C 530 m
• D 513 m

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Answer: D. 513 m

The sound travels to the surface and back, so 2d = speed x time = 342 x 3 = 1026 m. Hence d = 513 m.

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