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Homework Help: Angle of angular momentum

  1. Apr 14, 2005 #1
    I solved for 2 correctly but I can't figure out what to do for #3 Any help would be much appreciated. I think it might involve L = r x p , but I'm not entirely sure.

    2. [1pt]
    Two lightweight rods L = 20.5 cm in length are mounted perpendicular to a vertical axle and at 180° to each other (see figure below).

    At the end of each rod is a m = 602 g mass. The rods are spaced h = 35.7 cm apart along the axle. The axle rotates at 28.7 rad/s such that the angular velocity vector points upward (+). What is the component of the total angular momentum along the axle?

    3. What angle does the vector angular momentum make with the axle?

    Attached Files:

  2. jcsd
  3. Apr 14, 2005 #2


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    Homework Helper

    Did you get [tex]2mL^2w[/tex] for part 2?

    If it's only rotating about the vertical axle... then the answer in part 2 seems to be the only component so it seems to me the angle is 0.

    I'm wondering if the masses are also allowed to rotate counter-clockwise (due to their weight).
    Last edited: Apr 14, 2005
  4. Apr 15, 2005 #3
    yes that's what I used for part two.

    I tried 0 but it was wrong. So maybe they can rotate counter clockwise. How would that work?
    Last edited: Apr 15, 2005
  5. Apr 15, 2005 #4

    Doc Al

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    Staff: Mentor

    In general, the angular momentum of a body is not parallel to its axis of rotation. Find the total angular momentum about the center of mass by adding the angular momentum of each mass, which is given by [itex]\vec{L} = \vec{r}\times \vec{p}[/itex].
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