# Review problem help?

1. Apr 15, 2009

### fball558

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
forces.

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
post?

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

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!!