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S: 6/9/08 2:08 PM oldfinalexamAnswers.doc Page 1 of Physics 132 Final Exam
Moelter
• Partial credit will be awarded. However, you must show/explain your work. A correct
answer without explanatory material will not receive full credit.
• Clearly indicate your final result with a box or circle.
• If you need more space go onto the back and indicate "OVER''.
Equation sheet is the last page. You may tear it off if that is helpful.
These are just the
answers without any
work. As shown, they
would receive
essentially no credit.
In your solutions be
sure to include
pictures, word of
explanation, etc.
problem pts. possible score
1 10
2 10
3 10
4 5
5 10
6 10
7 10
8 15
9 10
10 10
Total 100
mjm 6/9/08 oldfinalexamAnswers.doc Page 2 of 8
1. (10 pts) A block (mass 0.5 kg) is hanging from the end of a spring. The spring is observed to
stretch by 20 cm in order to come to equilibrium.
a) What is the spring constant?
b) From the equilibrium position the block is now stretched by 10 cm and released from rest.
What is the period of the oscillations?
c) Write an equation that describes the motion of the block/spring system, y(t)=… .
d) What is the maximum speed of the mass and at which position does it have this speed?
k=24.5 N/m
!
" =
k
m
=7 rad/s
!
T = 2"
m
k
=0.90 s
!
y(t) = 0.10cmcos(7rad/s t + " )
!
v
max ="A=0.7 m/s
mjm 6/9/08 oldfinalexamAnswers.doc Page 3 of 8
2. (10 pts) a) The sinusoidal waveform shown is traveling to the right with a speed 40 m/s.
What is the frequency of the wave?
!
f =
v
"
=5 s-1= 5 Hz
b) A string (length=2.0 m) is held under tension so that the speed of waves on the string is 40
m/s. When vibrated the standing wave pattern is as shown:
What is the frequency of the vibrating source?
!
" = L /3,
!
f =
v
"
=60 Hz
-10 -8 -6 -4 -2 0 2 4 6 8 10
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
position (m)
displacement (m)
mjm 6/9/08 oldfinalexamAnswers.doc Page 4 of 8
3. (10 pts) a) You are walking away from two
identical speakers being driven by the same
source that are a distance d (! 0 ) apart and you
hear a maximum sound. What are the possible
values of d? The speed of sound is 340 m/s and
the frequency is 170 Hz.
!
"x = m# = m
v
f
= m(2m)
b) The top figure shows a sketch of the intensity pattern obtained on the wall some distance from
a double-slit. On the bottom figure indicate qualitatively what happens to the pattern if the slit
spacing is increased. (The dashed data is there for reference.)
d up,
theta down
4. (5 pts) Light is incident onto a water-air boundary at an angle of 52o relative to the normal.
The light starts in the water and goes toward the air. What are the angles of the reflected and
refracted light?
!
"air undefined or
!
"water >"c so no refraction, total internal reflection.
d
you
mjm 6/9/08 oldfinalexamAnswers.doc Page 5 of 8
5. (10 pts) A converging lens has a focal length of 15 cm. A 2 cm tall object is placed 10 cm
from the lens.
e) Sketch an appropriate ray diagram on the grid below.
f) Using your diagram find the location of the image, by how much it is magnified or reduced,
and whether it is upright or inverted.
g) Now calculate the image location, the amount of magnification or reduction, and whether it is
upright or inverted.
Do your numerical results agree qualitatively with your diagram?
s'=-30 cm, m=-s'/s=3, upright, virtual
mjm 6/9/08 oldfinalexamAnswers.doc Page 6 of 8
6. (10 pts) Consider the design shown for a heat engine. Is this a reasonable design? How do
you know?
satisfies first law
!
"=0.75, ok with Carnot
7. (10 pts) An engine cycle is shown on the p-V diagram. Part D is isothermal and part A is
adiabatic.
Fill in the chart below with +, - , or 0 to describe
the change in thermal energy ΔEth, the work done
by the environment W, and the heat added Q
during each part of the cycle.
ΔEth W Q
A - - 0
B - + -
C + 0 +
D 0 - +
ABCD
cycle
0 - +
T=800 K
T=200 K
100 J
25 J
75 J
p
V
A
D
B
C
mjm 6/9/08 oldfinalexamAnswers.doc Page 7 of 8
8. (15 pts) On the p-V diagram one mole of an ideal gas
is taken around the cycle shown a, b, c, d.
p0=3x105 Pa, V0= 0.2 m3
For this gas CP=(5/2)R and CV=(3/2)R.
a) What is the total work done during a cycle?
b) What is the total heat added or removed during each
part of the cycle?
c) What is the efficiency of the engine?
W=30,000 J
Qda=+45,000 J
Qab=+150,000 J
Qbc=-90,000 J
Qcd=-75,000 J
!
"=0.154
a
b
c
p
V
V0 2V0
p0
p0/2 d
mjm 6/9/08 oldfinalexamAnswers.doc Page 8 of 8
9. (10 pts) Two moles of an ideal monatomic gas are at pressure of 1 atm and T=310 K in a rigid
container.
a) What is the internal energy of the gas?
b) How much volume does it occupy?
c) If the temperature is changed to 450 K, what is the new pressure?
Eth=7,730 J
V=0.051 m3
pnew=1.45 atm
10. (10 pts) A 100 g piece of copper in taken from boiling water and put into an insulated,
covered container with 100 g of water at 15 oC. What is the final temperature?
for this exam specific heats given on eqn. sheet
Tf=22.1 oC
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