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Doppler effect with moving source and observer

  1. Mar 29, 2015 #1
    1. The problem statement, all variables and given/known data
    As you drive at a speed of 15.0 m/s an ambulance approaches you from behind with its siren blaring at a frequency of 1022 Hz. After the ambulance has passed you the signal is now 981 Hz. If both you and the ambulance travel at a constant speed how fast was the ambulance traveling?

    2. Relevant equations
    fo=fs(1+- vo/v)/(1+-vs/v)

    3. The attempt at a solution
    So I tried to use the equation above by plugging in the frequencies, but was trapped because the frequencies show only what the source was emitting, and not what the observer was hearing.
     
    Last edited by a moderator: Mar 30, 2015
  2. jcsd
  3. Mar 29, 2015 #2

    mfb

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    fo is the observer frequency.
    You don't have the source frequency, but you have a second equation you can use.
     
  4. Mar 29, 2015 #3
    What is the second equation?
     
  5. Mar 29, 2015 #4

    mfb

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    Staff: Mentor

    The ambulance before and after it passes you => 2 equations
     
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