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101Fa11Exam3VersionA.pdf-Physics 101 A Hour Exam III
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101Fa11Exam3VersionA.pdf-Physics 101 A Hour Exam III
##### Page 7
Physics 101
A
Hour Exam III
Fall
2011
Page 7 of 9
(23 problems)
The following question is by itself.
14.
A sound wave of frequency 1230 Hz has a speed of 410 m/s in medium A. The wave
enters medium B, where its wavelength is halved.
What is the speed of the wave in
medium B?
a.
410 m/s
b.
205 m/s
c.
820 m/s
d.
307 m/s
e.
615 m/s
The next two questions refer to the same situation.
As shown in the figure below, a string as attached at one end to a transducer. The string
runs over a smooth peg a distance L = 3.4 m from the transducer. A mass M is attached to
the end of the string opposite the transducer so that it hangs from the peg. The transducer
and the peg are fixed to be the same distance from the horizontal ground. The tension in
the string is controlled by the mass M. A standing wave of frequency f is produced
between the transducer and the peg. One instance of the standing wave is drawn in the
figure.
15.
What is the wavelength of the standing wave in the figure?
a.
3.4 m
b.
2.27 m
c.
5.1 m
d.
1.7 m
e.
4.54 m
16.
Now, to double the frequency (f
2f) while maintaining the same number of nodes,
the original mass M is replaced by a new mass m. What is the required ratio m/M?
a.
m/M = 1/4
b.
m/M = 1/2
c.
m/M = 1
d.
m/M = 2
e.
m/M = 4
L
M
transducer
g

##### Page 8
Physics 101
A
Hour Exam III
Fall
2011
Page 8 of 9
(23 problems)
The following question is by itself.
17.
Two identical sirens are placed 30 meters away from you.
From them you hear a sound
of loudness
0
.
How many sirens the same as these two sirens should be placed 60 m away
from you to produce the sound of the same loudness
0
?
a.
5
b.
6
c.
7
d.
4
e.
8
The following question is by itself.
18.
There is a siren at the side of a straight road. You drive a car toward it and then pass
it by. You hear the frequency of the siren to change from f
before
= 860 Hz to f
after
= 820 Hz.
What is the frequency of the siren measured by a stationary observer?
a.
840 Hz
b.
830 Hz
c.
850 Hz
d.
845 Hz
e.
835 Hz
The following question is by itself.
19.
A bimetallic strip is made from an aluminum strip placed at the left and an iron strip
placed at the right.
The linear thermal expansion coefficient of aluminum is 1.6
10
5
/K
and that of iron is 1.2
10
5
/K.
The bimetallic strip is straight at 300 K.
Now, the
temperature is increased to 370K. Which way does the bimetallic strip bend, to the iron
side (right) or to the aluminum side (left)?
a.
leftward (A)
b.
rightward (B)

##### Page 9
Physics 101
A
Hour Exam III
Fall
2011
Page 9 of 9
(23 problems)
The following question is by itself.
20.
There is a cubic box of size a.
When its temperature is raised from 230 K to 340 K,
its surface area increases by 2.2 %.
What is the % increase of its volume in the same
situation?
a.
1.5 %
b.
3.3 %
c.
2.2 %
d.
2.7 %
e.
4.4 %
The following question is by itself
21.
An ideal gas thermometer is a small rigid container of volume 120 cm
3
containing
0.03 moles of ideal gas.
From its pressure the temperature is measured.
The
thermometer is dipped in a liquid and, after thermal equilibrium is reached, the pressure
of the thermometer is 293 kPa. What is the temperature of the liquid?
a.
390 K
b.
141 K
c.
297 K
d.
401K
e.
323 K
The next two questions refer to the same situation.
A tank of volume 1.3 m
3
contains an ideal gas consisting of a chemical species A, whose
pressure is P = 490 kPa and temperature T = 320 K.
22.
How many molecules are there in the tank?
a.
0.31
10
24
b.
1.44
10
24
c.
1.12
10
25
d.
1.44
10
26
e.
0.31
10
26
23.
The root-mean-square velocity of the gas molecules is 257 m/s.
What is the
molecular mass of chemical species A? Express your answer in unit of unified atomic
mass u. 1 u = 1.66
10
27
kg.
a.
163 u.
b.
121 u.
c.
49 u.
d.
82 u.
e.
103 u.
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