Physics 53
Summer 2009
1
Exam II
Solutions
In questions or problems not requiring numerical answers, express the answers in terms of the
symbols given, and standard constants such as
g
. If numbers are required, use
g
= 10 m/s
2
.
Part A:
Multiple choice questions. Check the best answer. Each question carries a value of 4 points.
1.
A correct and general statement of the law of conservation of angular
momentum of a system is:
If the net external torque about any point is zero, the total angular
momentum about all points is conserved.
The product of the moment of inertia and angular velocity of a body is
conserved.
If the net external force on a system is zero, the total angular momentum
is conserved.
√
If a component of the net external torque about a point is zero,
that
component of the total angular momentum about that point is conserved.
2.
You move a heavy cylindrical oil drum of mass
M
up an incline at constant
speed, by applying a force with your hands at the top of the drum as shown. The
drum rolls up the incline without slipping. Which of the following is NOT true?
As the drum moves a distance
d
on the incline you do work
Mgd
sin
!
.
The static friction force is up the incline, with
magnitude
1
2
Mg
sin
!
.
The applied force has magnitude
1
2
Mg
sin
!
.
√
Half of the work done on the drum is done by static friction.
[Static friction never does work.]
3.
Satellite A’s orbit around the earth is a circle of radius 2
R
; satellite
B
’s orbit is an
ellipse with perigee distance
R
and apogee distance 3
R
. They have equal mass.
The total energy of A is greater than that of B. [Same]
The period of B is greater that that of A. [Same]
The largest speed of B is the same as the speed of A. [Larger]
√
When B is also at distance 2
R
from the center of the earth its speed is the
same as that of A.
θ
F
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Physics 53
Summer 2009
2
4.
An SUV rounds a curve on a level
road, moving at the instant shown
into the page. Its CM is at height
h
above the road, and the distance
between the wheels shown is
w
. The
question being posed is this: If its
speed increases beyond the
maximum safe value, will the SUV
slide outward on the curve or roll
over? Which of these is WRONG?
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 Spring '07
 Mueller
 Physics, Force, Total Energy

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