The echo (reflected sounD. will be distinctly heard only at ordinary temperatures if the distance of the reflecting surfaces from the source of sound is at least ________?
Correct answer: C. 56 ft
- A. 1120 ft
- B. 120 ft
- C. 56 ft
- D. 100 ft
- E. None of these
Explanation
A distinct echo requires the reflected sound to arrive at least 0.1 second after the direct sound. At about 1120 feet per second, the sound travels 112 feet in that time, so the reflector must be half that distance, or 56 feet, away.
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