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Homework Help: Wave Question

  1. Nov 28, 2007 #1
    1. The problem statement, all variables and given/known data
    A 22-cm-long, 1.0-mm-diameter copper wire is joined smoothly to a 60-cm-long, 1.0-mm-diameter aluminum wire. The resulting wire is stretched with 20 N of tension between fixed supports 82 cm apart. The densities of copper and aluminum are 8920kg/m^3 and , 2700 kg/m^3 respectively.

    a) What is the lowest-frequency standing wave for which there is a node at the junction between the two metals?

    b) At that frequency, how many antinodes are on the aluminum wire?
    2. Relevant equations
    v = sqrt(T/mu)
    v = lambda*f

    3. The attempt at a solution
    lambda = 2L
    L = 0.82m
    lambda = 1.64m

    v = lambda*f
    f = v / lambda
    f = v / (1.64m)

    v = sqrt(T/mu)
    v = sqrt(20/mu)

    d = mass / volume

    mu = mass / length

    ok...now the problem is, i dont' know which denstity (copper or aluminum) to use to figure out the mu. i tried using aluminum's since it's lower and hence will give the lower frequency, but it did not give the right answer. please help! thanks
  2. jcsd
  3. Nov 29, 2007 #2
    help any 1 ?
  4. Dec 9, 2007 #3
    I need help with this question too :/
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