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Homework Help: Mechanical waves question.

  1. Feb 15, 2010 #1
    1. The problem statement, all variables and given/known data
    A 403 Hz wave travels at 200 m/s along a wire.

    a)At a given time, the distance between points that differ in phase by 1.9 rad is ___ m.
    b)At a given position, the change in phase during an interval of 4.8 ms is ___ rad.

    2. Relevant equations
    V=w/k
    w=2pif

    3. The attempt at a solution

    I 've already solved for a), it was pretty straight forward. Now, I'm stuck on b)

    w=2pif
    =2pi*403
    =806pi

    v=w/k
    k=w/v
    =806pi/200
    =4.03pi

    delta phi = x/k
    = 1.9/4.03pi
    =0.15m
    this was for number 1... now I'm stuck on b)
    pls help....
     
    Last edited: Feb 16, 2010
  2. jcsd
  3. Feb 15, 2010 #2

    ehild

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    Homework Helper

    The wave is periodic both in time and position. The displacement in a sine wave is

    u=A*sin(2p(t/T-x/lambda)) or in other form u=A*sin(wt-kx),

    with w=2pi/T and k=2pi/lambda.

    The term 2pi(t/T-x/lambda)=wt-kx is the phase of the wave.

    T is the time period and the period in space is lambda. At a given time t, two points which are lambda distance apart differ by 2pi in phase. At a certain position x, the phase changes by pi during T time interval.

    You know the frequency f, so you know the time period T=1/f. The elapsed time is given, dt=4.8*10-3 s, what is the phase difference between t and t+dt?

    ehild
     
  4. Feb 16, 2010 #3
    Thank you!!
     
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