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32. We use a righthanded coordinate system with
#
k
directed out of the
xy
plane so as to
be consistent with counterclockwise rotation (and the righthand rule). Thus, all the
angular momenta being considered are along the –
#
k direction; for example, in part (b)
G
A
=−
40
2
.
#
t
k in SI units. We use Eq. 1123.
(a) The angular momentum is constant so its derivative is zero. There is no torque in this
instance.
(b) Taking the derivative with respect to time, we obtain the torque:
()
2
ˆˆ
4.0k
( 8.0 N m)k
dd
t
t
dt
dt
τ
==
−
=
−
⋅
G
A
G
.
This vector points in the –
#
k direction (causing the clockwise motion to speed up) for all
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 Spring '08
 Any
 Physics

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