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Sound waves problem

  1. Aug 21, 2005 #1
    Can someone help me with this question, im stucked

    A and B are two observers 1km apart . There is a steady wind blowing . When a gun is fired at A the time interval between the flash and report observed at B is 3.04s. When a gun is fired at B the time interval between the flash and report observed at A is 2.96s.
    Calculate the valocity of sound in air and velocity component of wind in direction BA.

    do i use the formula f=v/wavelenght or velocity=distance/time?
     
  2. jcsd
  3. Aug 21, 2005 #2

    Tide

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    Think it through. How would the frequency/wavelength relation even be of any help? What speed would you put into it?

    The problem is asking for the speed of sound and it gives you information about the travel times and the distance traveled. Which formula do you think would be helpful?

    Once you decide that here's a hint:

    The speed of sound relative to the ground must take into account that the fact that the sound is travelling through a medium that is itself moving.
     
  4. Aug 21, 2005 #3
    but it did not give me the distance between the gun and A.
    does it mean i use 1km?
     
  5. Aug 21, 2005 #4

    Tide

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    "The gun is fired at A and the report is observed at B" .... therefore ...?
     
  6. Aug 22, 2005 #5

    HallsofIvy

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    No, "at" does not mean "1 km away"! :smile:

    Wavelength and frequency relations are useless here because you are not told either of those.

    Let u be the speed of sound, v be the speed of the wind. Since wind is moving air and sound moves through the air, the net speed of sound, in the direction the wind is blowing, is u+ v. The net speed of sound, in the opposite direction, is u- v. Does that help?
     
    Last edited: Aug 22, 2005
  7. Aug 22, 2005 #6
    thanks..i think i understand now .but how do i find the velocity of the wind?
     
  8. Aug 22, 2005 #7

    EnumaElish

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    You have two unknowns, u and v. You need to come up with two equations that you need to solve simultaneously to figure out u and v together.

    A has a gun, and B has a gun. A fires, B listens. Then B fires, A listens.
     
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