物理 wave - Ans.fyi 參考答案

物理 wave

2011-09-14 3:14 am

1. A person sees a heavy stone strike a concrete pavement. A moment later two sounds are heard from the impact: one travels through the air and the other through the concrete, and they are 1.4 apart. How far away did the impact occur? The speeds of the sound in air and in concrete are 340 ms-1 and 5000ms-1 respectively.

回答 (1)

天同

2011-09-14 3:30 am

✔ 最佳答案

I presume that the two sounds are heard at a time interval of 1.4 seconds apart the unit has not been given in your question.

Let d be the distance from the person where the impact occurred.
Hence, d = 5000t
where t is the time for the sound wave to travel from the point of impact to the person through the concrete.

For sound wave that travels through air, d = 330(t + 1.4)
Hence, equating the two equations,
5000t = 330(t + 1.4)
solve for t gives t = 0.1002 s

Substitute the value of t into the 1st equation,
d = 5000 x 0.1001 m = 501 m

2011-09-13 19:35:56 補充：
sorry, there are some typos.
The 2nd equation should be d = 340(t+1.4)
hence, 5000t = 340(t+1.4)
thus, t = 0.102 s
and d = 5000 x 0.102 m = 511 m

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