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Review problem help?

  1. Apr 15, 2009 #1
    Review problem help??

    1. The problem statement, all variables and given/known data

    Im finishing up studying for my physics exam tonight. i ran into a couple problems i did not know how to do, and the help room is packed. so i figured i would try here again seeing you guys know what your talking about just as much as them (if not better)
    here is the problem, sorry it is so long

    A standard bicycle wheel with extra mass
    filling the tire is set spinning rapidly about a long axle.
    (pretty much just a solid disk, they word it funny)
    One end of this axle rested on a holder at the top of a
    large mounting post, which allows the gyroscope to
    rotate freely about the vertical post. The spinning
    gyroscope was mounted on the post initially pointed
    straight up, but gradually it tipped over and began
    precessing about the vertical direction (meaning that the
    spinning gyroscope was also sweeping out a circular
    path in a horizontal plane).

    A. Eventually the gyroscope axle is completely horizontal, similar to what is
    shown in the figure, while precessing about the mounting post. In this configuration, list
    the most significant forces acting on the gyroscope and describe the vector sum of these

    B. The mass of the outer part of the bicycle wheel is 4.1 kg, the radius of the
    wheel is 0.33 m, and the wheel is spinning at 6.0 revolutions per second. What is the
    magnitude of the wheel’s angular momentum about its axle?

    C. At a certain instant the angular momentum
    of the wheel about its axle is exactly in the +x direction:
    Lo = Lo ˆx. (The free tip of the axle is also pointing in this
    direction.) The total length of the axle is 0.30 m, and the
    wheel is attached at the midpoint. What is the torque on
    the gyroscope about the end of the axle on the mounting

    D. At a time t=0.10 s later, what is the (approximate) angular momentum of the

    E. You have shown above what the direction of the torque due to gravity is,
    and hence what direction the axle (and L) will move on account of the gravitational
    torque. Can gravity cause the axle of the spinning bicycle wheel to tilt downwards (-y
    direction)? Why or why not? Why doesn’t the wheel just fall down, the way a nonspinning
    wheel would?

    any help would be GREAT!!
  2. jcsd
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