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Homework Help: Angular Momentum tricky problem

  1. Oct 20, 2013 #1
    1. The problem statement, all variables and given/known data
    As the picture shows, we are given several variables, but I am near completely lost. I am behind in my course and am trying to catch up as best as I can but this problem is really hard for me

    2. Relevant equations

    The equations that I have used are;

    parallel axis theorem
    angular acceleration = tangential acceleration*radius

    3. The attempt at a solution
    I know that this solution will be completely wrong as I haven't utilised the frictional torque, nor the angle.

    So, by applying the parallel axis theorem for the mass moment of inertia;

    I0 = I + mr^2
    I(slender bar) = 1/12 * m * L^2
    ∴ I0 = 1/12 * m * L^2 + mr^2

    then used the fact that:

    ƩM0 = I0:

    and therefore:

    mgb = I0 * angular acceleration:
    where b is the distance from the COM

    however, as assumed, this gave the wrong answer, I'm really stuck with it and I want to know how I can do it for problems to come. Thanks!! :D
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

  2. jcsd
  3. Oct 20, 2013 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    You need to show your calculations.

    Your equation for the sum of the moments = I0 is incomplete.

    How are we to know what you've done if you don't provide your work?
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