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Waves and sounds, finding the speed of a jet using the speed of sound

  1. Jan 23, 2012 #1
    1. The problem statement, all variables and given/known data

    A jet is flying horizontally, as the drawing shows. When the plane is directly overhead at B, a person on the ground hears the sound coming from A in the drawing. The average temperature of the air is 20 oC. If the speed of the plane at A is 180 m/s, what is its speed at B, assuming that it has a constant acceleration?

    http://edugen.wileyplus.com/edugen/courses/crs2216/art/qb/qu/c16/ch16p_101.gif


    2. Relevant equations
    x=1/2(Vo+V)t
    V=λ/Period (T)= λ x Frequency
    c (speed of sound)= 343 m/s at 20 degrees celsius
    T (period)= 2 ∏/ω(angular frequency)

    3. The attempt at a solution

    first I tried to use the kinematic equation to find the distance between the points A and B but I am stuck because i need the time in order to find the distance (x) between the two points. I think I need to use the pythagorean theorem because the angle made by point B is 90 degrees and I am giving the angle of the observer on the ground as 36 degrees, meaning that the last angle should be 54 degrees to add up to 180 degrees. Do I need to use the law of cosines or sines since I know three angles? any help is appreciated
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

    Last edited: Jan 23, 2012
  2. jcsd
  3. Jan 23, 2012 #2
    Can't view your picture.
     
  4. Jan 24, 2012 #3
    In your image, the right triangle has sides (using your formula), (v_0 + v)*t/2 , h, c*t.

    The length (v_0 + v)*t/2 is related to the length c*t using some trig. t will cancel.

    This is late, hope it helps.
     
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