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Homework Help: Acceleration of a rod

  1. Oct 26, 2007 #1
    1. The problem statement, all variables and given/known data
    A solid rod of mass M = 2.48 kg and length L = 45 cm is suspended by two strings, each with a length d = 35 cm (see Figure), one at each end of the rod. The string on side B is cut. What is the magnitude of the initial tangential acceleration of end B?
    The string on side B is retied and now has only half the length of the string on side A. What now is the magnitude of the initial tangential acceleration of end B?

    2. Relevant equations

    alpha = I/T

    I = r(alpha)

    I = 1/3MR^2

    3. The attempt at a solution
    I'm completely loss really. When string B is cut and it proceeds to swing down would the length of it's string d be counted into the radius? I don't really know what I'm doing here.
  2. jcsd
  3. Oct 26, 2007 #2


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    No, don't count the string length in the radius, the rod pivots about its end such that its radius is the same as it length. What you need to find is the initial Torque of the rod's weight from its cg about the pivot. It is different for each case. And correct your second relevant equation to read a_tangential = r(alpha).
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