Physics 7A: Quiz 5
UC Berkeley, Fall 2010, GSI: Aaron Alpert
Question 1.
The rope shown in the figure is wound
around a cylinder of mass 4
kg
and
¯
I
=
.
02
kg
·
m
2
,
about the cylinder’s axis. If the cylinder rolls without
slipping, what is the linear acceleration of the center of
mass? What is the frictional force? [Hint: Use an axis
of rotation through the CM.]
Question
2.
Sarah
is
standing
motionless
on
a
turntable, holding a bicycle wheel horizontally directly
over her head, as shown in the figure. The wheel’s an
gular velocity is 6
rad/s
in the +
k
direction. Suddenly,
Sarah twists the wheel so that now, the wheel’s CM is still directly over her head, but the wheel
is vertical. In what direction, and at what speed, does Sarah rotate? Treat the bicycle wheel as a
ring with mass 10
kg
and radius
.
3
m
. Treat Sarah as a cylinder with mass 60
kg
and radius
.
25
m
.
For a ring
I
z
=
mR
2
and
I
x
=
1
2
mR
2
, where
I
z
is the moment of inertia about the central axis,
and
I
x
is the moment of inertia about a vertical axis. For a cylinder,
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 Spring '08
 Lanzara
 Physics, Acceleration, Angular Momentum, Mass, Moment Of Inertia, Rigid Body, Aaron Alpert

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