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73. We choose positive coordinate directions (different choices for each item) so that
each is accelerating positively, which will allow us to set
aa
R
12
==
α
(for simplicity,
we denote this as
a
). Thus, we choose upward positive for
m
1
, downward positive for
m
2
and (somewhat unconventionally) clockwise for positive sense of disk rotation. Applying
Newton’s second law to
m
1
m
2
and (in the form of Eq. 1045) to
M
, respectively, we
arrive at the following three equations.
Tm
gm
a
mg T
ma
TR TR I
11
1
1
22
2
2
21
−=
(a) The rotational inertia of the disk is
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 Spring '08
 Any
 Physics

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