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distance from the distance of the three
the geometry, the central hydrogen to the
atoms on the vertex. if the distance beH nuclei from the rotation axis is
tween the hydrogens is a, then the radius
ais 3 , where a is the length of a side
/
a2
a
a1
r=
of the tetrahedron. ◦ = √ = √ .
2 cos 30 2 3 H C
H H H
a 3 Apply the definition of the moment
So, we ﬁnd that
of inertia for a system of particles to
I=
obtain: I = ∑ mi ri 2 = mH r12 + mH r22 + mH r32 Substitute numerical values and
evaluate I: I = 1.67 × 10 − 27 kg 0.18 × 10 −9 m i 2 2
3mH
⎛a⎞
⎟ = mH a 2
=
mH= 3mH ⎜
a
⎝ 3 ⎠2
= (1.67 × 10−27 ) (0.18 × 10−9 )
=
5.41 × 10−47 kg m2 .
a
√
3
2 ( )( = 5.4 × 10 − 47 kg ⋅ m 2 2 ) 2 ⎝
⎠
us sign is a consequence of the fact that the frictional torque
otion of the wheel.
3. A pendulum consisting of a string of length L attached to a bob of mass m swings in
a vertical plane. When the string is at an angle θ to the vertical, endulum consisting tangentialstring of length L attached to a bob of
(a) c...
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This document was uploaded on 03/14/2014 for the course PHYS 18 at UC Merced.
 Spring '10
 collins
 Physics, Work

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