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How much of the reflected sound is heard by person A?

  1. Jun 12, 2017 #1
    1. The problem statement, all variables and given/known data

    IMG_1157_2.png
    IMG_1158_1.png

    2. Relevant equations

    Doppler's Equation

    3. The attempt at a solution
    (1)
    freqA = (v sound - vA )/(v sound - v B) . freq B
    *v A = 0 (static)
    = V/(V - v) . freq B .....Answer : (d)

    (2) freq A hear which is reflected sound by D
    first find freq D, *v D, v A = 0 (static)
    freq D received from B = (v sound - v D) / (v sound + v B) . freq B
    freq D = V / (V + v) . Freq B
    freq A = (v sound - v A) / (v sound - v D) . freq D
    freq A = V / V . freq D
    freq A = V / (V + v) . Freq B ........Answer : (c)

    (3) can someone give me clue about this one?

    (4) freq C = (v sound + v C) / (v sound - v B) . freq B
    freq C = (V + v) / V . Freq B...... Answer : (a)

    (5) freq A which reflected by D
    freq D received from B = (v sound + v D) / (v sound - v B) . freq B
    freq D = (V + v)/V . freq B
    freq A received from D = (v sound - v A)/(v sound - v D). freq D
    freq A = (V) / (V - v) . (V + v) / V . freq B
    freq A = (V + v) / (V - v) . freq B ....Answer : (e)


    are the other numbers also in right way?
     
  2. jcsd
  3. Jun 12, 2017 #2

    BvU

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Hello again,

    I think you did fine applying the relevant equation you give.
    but for (3) you need another relevant equation involving the answers for (1) and (2). Easily found if you google beat frequency.
     
  4. Jun 13, 2017 #3
    (3) f beat = absolute (f2 - f1)
    F beat = absolute ( f reflected - Aa)
    F beat = abs f(V / (V + v) ) - f( V/(V -v) )
    F beat = abs fV(V-v) - (V + v) / (V^2 - v^2)
    F beat= abs f.V(-2v)/(V^2 - v^2)
    F beat = 2Vv / (V^2 - v^2).f
     
  5. Jun 13, 2017 #4
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