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Doubts on angular momentum [master's degree exam]

  1. Sep 3, 2015 #1
    • Homework template is missing; originally posted in non-homework forum
    Two hollow spheres, both the mass and radius R M , which are rotating around a center of mass ( CM ) , with an initial period To, are kept distant from each other by an ideal wire with a distance of 8R. At a given instant a motor is driven by wrapping the wire and making the two spheres meet. Consider the inertia moment motor despicable , and disregard the effects of gravity . Express all your results in terms of M, R and To. Consider the angular momentum of the spherical shell 2 / 3MR2

    a) determine the angular momentum of the system relative to the center of mass of time before the engine is started .

    b ) determining the angular velocity of rotation at the time when a ball contacts the other

    I Solved the a) like this

    L = I.w
    L = (2/3 MR²) . (2π(4R))/T0.(4R)
    L = (4/3 MR²)/ T0

    that's the angular momentum for 1 shell. multiply that by 2 to get the angular momentum to the sistem.

    L = (8/3 MR²)/T0

    But I can't solve the B part. I've tried everything I could, but I cant make the angular velocity at the contact situation in terms of T0.

    Help plz ;)....
    sorry about my english. I'm not fluent.

    Attached Files:

  2. jcsd
  3. Sep 3, 2015 #2

    Doc Al

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    Staff: Mentor

    You need the moment of inertia of each sphere about the axis of rotation. Use the parallel axis theorem.
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