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Sound Waves of explosion

  1. Mar 9, 2007 #1
    1. The problem statement, all variables and given/known data
    An explosion occurs at the end of a pier. The sound reaches the other end of the pier by traveling through three media: air, fresh water, and a slender metal handrail. The speeds of sound in air, water, and the handrail are 343, 1482, and 5040 m/s, respectively. The sound travels a distance of 150 m in each medium.
    (a) Through which medium does the sound arrive first, second, and third?

    (b) After the first sound arrives, how much later do the second and third sounds arrive?

    2. Relevant equations

    3. The attempt at a solution

    We just started going over waves and sound so I'm not sure how to figure out this problem.
    For part (a) I figured out that the sounds arrives first at the steel handrail, then freshwater then air.
    For part (b) I don't know how to figure that out. I tried just doing how many seconds it would take to travel 150m for each substance, but I don't think that's right.
  2. jcsd
  3. Mar 9, 2007 #2


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    Well, the problem states the speed of sound in each medium, so you can get how long it takes in each medium using,

    time = distance/velocity
  4. Mar 9, 2007 #3
    So first it went through the steel handrail so that is 150/5040= 0.02976s, then through the water so 150/1432= 0.1047s, then the air so 150/343=0.4373s.
    So the first sound happens after 0.03s, then the second sound comes after 0.1047s, then the third sound comes after 0.4373s. Right?
  5. Mar 9, 2007 #4
    I get that the third sound comes 0.41s because you have to do 0.437-0.03, but I can't figure out how to get the second sound...?
  6. Mar 9, 2007 #5
    The question asks how much later do the second and third arrive as compared to the first. You have done most of the work.
  7. Mar 9, 2007 #6
    Well for the second I did 0.105-0.03 and it's incorrect...?
  8. Mar 10, 2007 #7


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    This implies that the sound travels in parallel throught the media, not through each in turn.
    Otherwise it would always arrive in the last medium in the chain making the question meaningless.
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