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4/25/08 10:34 AM
Ch10 HW2 S2008
Page 1 of 6
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Ch10 HW2 S2008 (Homework)
KRISTIN SEILOFF
Instructor: Jennifer Curtis
Description
Rotational and translational angular momentum; Rotational kinetic energy
Instructions
Section 10.2
In this assignment you are allowed 3 submissions per numeric question
part, and 2 submissions per multiple choice question part
Web
Assign
Current Score:
26 out of 26
Due:
Friday, April 4, 200808:35 AM EDT
1. 3/3 points
Mounted on a low-mass rod of length
0.32
m are four balls. Two balls (shown in red on the diagram), each of mass
0.61
kg, are mounted at
opposite ends of the rod. Two other balls, each of mass
0.31
kg (shown in blue on the diagram), are each mounted a distance
0.08
m from the
center of the rod. The rod rotates on an axle through the center of the rod (indicated by the "x" in the diagram), perpendicular to the rod, and it
takes
0.9
seconds to make one full rotation.
(a) What is the moment of inertia of the device about its center?
= 0.035
0.0352
kg·m
2
(b) What is the angular speed of the rotating device?
= 6.98
6.98
radians/s
(c) What is the magnitude of the angular momentum of the rotating device?
= .246
0.246
kg·m
2
/s
Solution or Explanation
(a) Each mass contributes an amount
mr
2
to the moment of inertia, so
I
= 2m
1
r
1
2
+ 2m
2
r
2
2
(b)
= 2
/
T
.
(c) The angular momentum is
.

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4/25/08 10:34 AM
Ch10 HW2 S2008
Page 2 of 6
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2. 8/8 points
Moments of intertia for some objects of uniform density:
disk
I
= (1/2)
MR
2
, cylinder
I
= (1/2)
MR
2
, sphere
I
= (2/5)
MR
2
(a) A uniform disk has a moment of inertia that is (1/2)
MR
2
. A uniform disk of mass
12
kg, thickness
0.5
m, and radius
0.8
m is located at the
origin, oriented with its axis along the y axis. It rotates clockwise around its axis when viewed from above (that is, you stand at a point on the +y

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