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Homework Help: Reflection and Transmission (Waves in strings)

  1. Nov 7, 2007 #1
    1. The problem statement, all variables and given/known data

    Two copper wires, one 1.0 mm in diameter and 1.0 m long, the other 2.0 mm in diameter
    and 2.0 m long, are joined together end-to-end and hung vertically. In order to tension
    this compound wire, a block is suspended from it. It is found that a transverse pulse takes
    50 ms to travel the length of the joined wires. What is the mass of the block? The density
    of copper is 8920 kg/m3. (Hint: Given the volume mass density and diameters of the
    wires, how can we find their linear mass densities?)

    2. Relevant equations

    v=square root (T/Mu)
    Sum of All Forces=0
    v=wave speed
    T=Tension of string/wire
    Mu=mass/length of string in units kg/m
    V=volume of cylinder

    3. The attempt at a solution

    We started by finding Mu with the above equations to be 7.0e-3 kg/m for wire one and 2.8e-2 kg/m for wire two, respectably. What we do not understand is the relationship between the pulse time (50 milli-seconds), length of wire (3m) and the wavespeed. We think that after finding the wavespeed of the pulse we can use Newtons law to find the mass attached to the tensile forces. Any suggestions?
  2. jcsd
  3. Nov 7, 2007 #2
    Perhaps using the a sine function and v(wavespeed)=lambda/T(period) we could determine the wavespeed by inputing Pi/2 for T and 50ms for lambda?
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