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Homework Help: Is my solution right or wrong ?

  1. Oct 31, 2004 #1
    My question follow with my work to solve the question is in the attachment .

    Attached Files:

  2. jcsd
  3. Oct 31, 2004 #2
    "Selected zip file is invalid or corrupted"
  4. Nov 1, 2004 #3
    Don't worry

    don't worry, the file will not harm your computer.Just zip it and mu solution is in there.
  5. Nov 1, 2004 #4


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    Homework Helper

    The file contains a windows excel document with a picture:

    There a string (copper wire?) attached to an oscillilator at one end (point A). The other end of the string is hung over a pulley (point B) and a mass tied to the end of the string.
    The problem is:
    The length AB of the copper wire (the dot line) used in this experiment is 1.5m and its cross sectional area is 0.059mm^2
    The tension in the wire is 2.0 N. If the density of the copper is 8.9 x 10^3 kg/m^3 ,show that the lowest frequency to obtain a stationary wave is about 10Hz.

    Sanosuke's solution is:
    Pressure [itex]P=\frac{2}{0.059\cdot 10^{-6}}=33898305 Pa[/itex]
    [tex]V=\sqrt{\frac{33898305}{8.9 \cdot 10^3}}=61.72 m/s[/tex]

    V=fl (l is wavelength)

    [tex]f=\frac{V}{l}=\frac{V}{4 \cdot 1.5}=\frac{61.72}{6}=10.3 Hz \approx 10 Hz[/tex]
    Last edited: Nov 1, 2004
  6. Nov 1, 2004 #5
    Can I conceive the system to be an air column with one end closed as the l(wavelength) is equal to 4L ?

    By this way, I can obtain the answer to be at least 10Hz.
  7. Nov 2, 2004 #6


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    Gold Member

    Here treat it as a rope with both ends tied to a wall.

    The Mass is given so that the tension in the rope "T=Mg" can be found
    Also the mass per unit length [tex] \mu [/tex] can be found using the given data

    then the velocity of the wave in the string will be
    [tex] v= \sqrt \frac{T}{ \mu} [/tex]

    Using the velocity and the fact that the wavelength will correspond to
    [tex] \frac{n \lambda}{2} [/tex]
    The frequency can be found
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