Ch10 HW2 (Homework)
BRANDON JARROTT FELDKAMP
PHYS 2211, section M, Fall 2008
Instructor: Jennifer Curtis
Web
Assign
Current Score:
41 out of 42
Due:
Friday, November 7, 2008 09:00 AM EST
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
The due date for this assignment is past.
Your work can be viewed below, but no changes can be
made.
1. [MI2 10.X.09.01] 3/3 points
Mounted on a lowmass rod of length
0.48
m are four balls. Two balls (shown in red on the
diagram), each of mass
0.92
kg, are mounted at opposite ends of the rod. Two other balls, each of
mass
0.23
kg (shown in blue on the diagram), are each mounted a distance
0.12
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
1.5
seconds to make one full rotation.
(a) What is the moment of inertia of the device about its center?
=
.1126
0.113
kg·m
2
(b) What is the angular speed of the rotating device?
=
4.189
4.19
radians/s
(c) What is the magnitude of the angular momentum of the rotating device?
=
.4717
0.472
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
Ch10 HW2
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(b)
= 2
/
T
.
(c) The angular momentum is
.
2. [MI2 10.X.09] 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
14
kg,
thickness
0.5
m, and radius
0.5
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
axis and look toward the origin at the disk). The disk makes one complete rotation every
0.1
s.
What is the rotational angular momentum of the disk?
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 Spring '09
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 Physics, Current, Angular Momentum, Kinetic Energy, Work, Moment Of Inertia, Krot

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