A child claps once. The sound reaches a wall 17 m away and reflects back. The child hears a distinct echo because:
AThe wall is louder than the clap
BWalls always make echoes
CEchoes are independent of distance
DThe round-trip distance is 34 m, taking ~0.1 s — the minimum time for distinct echo perception
Answer & Solution
Correct answer: D. The round-trip distance is 34 m, taking ~0.1 s — the minimum time for distinct echo perception
Sound travels 17 m to wall + 17 m back = 34 m in air. Time = 34/340 = 0.1 s. This is the minimum time for the human brain to perceive an echo as distinct from the original sound. Closer than 17 m, no clear echo.
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