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Homework Help: What is the terminal speed of the paratrooper?

  1. May 26, 2008 #1
    1. The problem statement, all variables and given/known data
    A helicopter drops a paratrooper carrying a siren that emits a 788 Hz audible signal. The microphone (reciever) on the plane monitors the signal from the transmitter as the paratrooper falls. Take the speed of sound in air to be 343 m/s and assume the paratroopers always remains below the helicopter. If the perceived frequency becomes constant at 412 Hz, what is the terminal speed of the paratrooper? Answer in units of m/s.

    2. Relevant equations
    Not sure... could you guys help me out.

    Possibly Speed = wavelength * frequency ??

    3. The attempt at a solution
    Probably would need an equation first.
  2. jcsd
  3. May 26, 2008 #2
    Try and use your knowledge of the doppler effect for this.
  4. May 26, 2008 #3
    I don't really know much about it.

    f' = f [(v+v1)/(v-v2)]

    that's the equation. could you please walk me through this problem.
  5. May 26, 2008 #4
    Ok so the doppler effect is the apparent change in frequency of a wave due to the motion of the source or the observer.
    So f' is the observed and f is the frequency of the source.

    [tex] f' = \frac{fv}{v\pm u} [/tex]

    where v is the speed of sound and u is the speed of the source or the observer.
    If the source is approaching you it is v - u and if it is moving away it is v + u.
    Last edited: May 26, 2008
  6. May 26, 2008 #5
    Okay. That was very helpful. I got the answer of 313.03.

    I submitted online and it is correct.

  7. May 26, 2008 #6
    No problem, happy to help.
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