12.90. Model:
Model the skater as a cylindrical torso with two rodlike arms that are perpendicular to the
axis of the torso in the initial position and collapse into the torso in the final position.
Visualize:
Solve:
For the initial position, the moment of inertia is
1T
o
r
s
o
A
r
m
2.
II
I
=+
The moment of inertia of each arm is
that of a 66 cm long rod rotating about a point 10 cm from its end, and can be found using the parallelaxis
theorem. In the final position, the moment of inertia is
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 Fall '09
 geller
 Angular Momentum, Inertia, Moment Of Inertia, kg, Initial Position, final position

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