Two friends stand at opposite ends of a long steel fence, 340 m apart. One taps the fence; the other has her ear against the fence. She hears the tap travelling through:
AOnly through steel
BOnly through the air (single sound)
CNeither — sound cannot travel along a fence
DThrough steel and through air — and these two sounds reach her at different times because sound travels much faster in steel than in air
Answer & Solution
Correct answer: D. Through steel and through air — and these two sounds reach her at different times because sound travels much faster in steel than in air
Sound from the tap travels both through the steel fence (much faster — ~5000 m/s) AND through the air (~340 m/s). The two pulses reach the listener at slightly different times — through steel almost instantly (340/5000 = 0.068 s), through air about 1 s later. The 0.93 s gap is well above the 0.1 s threshold to hear them as separate sounds.
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