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Homework Help: Wave on a string tied to a weight

  1. Dec 30, 2009 #1
    1. The problem statement, all variables and given/known data
    A 17 m string of weight 13kg is tied to the ceiling at its upper end, and the lower is tied to a weight of 13 kg. how long will it take a wave to get from one end to the next? (g=10 m/s^2)

    2. Relevant equations
    v = (T/u)^(1/2)

    3. The attempt at a solution
    well, i think mass(y)=(13+13y/17)kg
    therefor T=ma= (13+13y/17)kg*19m/(s^2)
    V(y)=(T/u)^(1/2)=>> (10y)^1/2

    beyond this point i'm stuck. Thanks in advance.
  2. jcsd
  3. Jan 1, 2010 #2

    Doc Al

    User Avatar

    Staff: Mentor

    OK, this is the total mass for all points below y (measured from the bottom of the string).
    Where did you get 19 m/s^2? The tension at point y is equal to the weight of the mass below that point.
    Not sure where this last expression came from. Use the correct expression for T(y).

    V(y) = (T/μ)^(1/2)
    dy/dt = (T/μ)^(1/2)

    Rearrange and integrate to find the total time.
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