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Homework Help: Propagating waves along a non uniform string.

  1. Dec 7, 2013 #1
    1. The problem statement, all variables and given/known data
    The linear mass density of a non uniform wire under constant tension decreases gradually along the wire so that the incedent wave is transmitted without reflection. the wire is uniform for* -∞≤x≤0
    In this region, a transverse wave has the form y(x,t) = 0.003cos(30x − 60t). From x=0 to x=20 the linear mass density decreases fromμ to μ/9 and is again constant as μ/9 from x=20 to x=∞
    i. what is the wave velocity for large values of x(>20)?
    ii.What is the amplitude of the wave for large values of a(>20m). you should get this from conservation of mechanical energy.
    iii.What's y(x,t) for x=20 to x=∞.

    2. Relevant equations


    3. The attempt at a solution

    for part i. I used the above equation to equate the value of force for a wave from - infinity to 0 and 20 to infinity as the tension is uniform throughout the string and solved for the velocities in terms of each other. However I don't understand how to get a numerical answer.

    for part ii and iii I am struggling to see even how to approach this question :(

    any help would be most welcome.
  2. jcsd
  3. Dec 7, 2013 #2


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    What's the speed of the wave for x<0? You should be able to figure that out from the y(x) given to you.

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