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Doppler Effect question

  1. Nov 6, 2013 #1
    1. The problem statement, all variables and given/known data
    Two trains are traveling toward each other at 30.0 m/s relative to the ground. One train is blowing a whistle at 480 Hz. (a)What frequency is heard on the other train if the wind is blowing at 30.0 m/s toward the whistle and away from the listener? (assume the speed of sound is 343m/s)

    2. Relevant equations
    F'=F((V+V_d)/(V-V_d))



    3. The attempt at a solution
    Well the top velocity has a + and the bottom has a minus because they're going towards each other and the wind is going away from the listener and towards the source.
    So I just assumed F'=480((343+30+30)/(343-30+30)) since this is the vector sum? This is wrong however and it's actually the opposite, so I need help understanding why conceptually
     
  2. jcsd
  3. Nov 6, 2013 #2

    haruspex

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    You need to take each speed relative to the medium.
     
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