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Homework Help: Single Plane?

  1. Oct 21, 2007 #1
    1. A mass is hitting the end of a hinged rod. After impact they begin to rotate.
    The motion is then confined to a single plane. why? what plane?

    3. I am a bit confused by what they mean by a single plane. Are they saying that there are only x,y coordinates? Is this just a condition for the conservation of angular momentum or a reason why linear momentum cannot apply?
  2. jcsd
  3. Oct 21, 2007 #2


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    The motion of any point on a hinged object is always confined to a single plane in the lab-frame. This is the plane that is normal to the axis provided by the hinge.

    Consider, for example, the motion of the keyhole on a door, as the door rotates.
  4. Oct 21, 2007 #3
    I'm sorry but I still don't understand why it has to be considered in the single plane?
  5. Oct 21, 2007 #4
    The motion of the mass and the rod is a circle. Circle lies in a place, perpendicular to the angular momentum vector of the objects moving round the hinge... I think
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