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Homework Help: Finding direction of angular momentum of system~

  1. Dec 14, 2015 #1
    1. The problem statement, all variables and given/known data
    A rod that is fixed to a vertical wall is attached through the middle of a solid disk. A piece of the disk crumbles off when the disk is spinning and rises vertically. The system is the chip and the spinning disk.
    Assume no friction.

    A. How does the direction of the angular momentum of the system vary as the chip flies upward?

    B. How does the direction of the disk's spin affect the systems angular momentum?

    2. Relevant equations

    3. The attempt at a solution

    A. Since the chip's speed decreases, I would wager that the system "varies" by decreasing?

    B. I have no idea how the disks spin contributes to the system angular momentum. I know the direction of the angular momentum vector for the disk is in the same direction of its angular velocity (horizontally in the picture). How do I find the direction and shape of a angular momentum vector for a system though?
    What if the disk were spinning different directions? I never thought that would affect the angular momentum of the system....
    Anyway, I would appreciate opinions on the issue.
  2. jcsd
  3. Dec 15, 2015 #2


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    Science Advisor
    Homework Helper
    Gold Member

    The question asks how the direction of the angular momentum changes. You stated, correctly, that the magnitude decreases, but that is not what was asked.
    I'm not at all sure what B is asking. There is no description of any proposed change to the direction of the disk's spin. Are we to consider the rod not being horizontal? If so, the chip will not go vertically, which does make matters more interesting. Or did they mean the sense of the spin?
    To answer your question about angular momentum of a system, just add the angular momentum vectors of its components.
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