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Unformatted text preview: NAME: _—KEY___— WebCT ID: Cal Poly University Pomona
Physics Department
PHY 13201 50minute MidTerm # 2
S. Chakravarti OPEN book — NO notes
Answer ALL 15' questions (each question is worth 10 points) You may write on the test.
Please WRITE your name on the scantron.
Please return the test with the scantron. 1. Two traveling waves are given by
y1(x, t) = ym sin(k:r — wt) and y2(:r, t) :2 ym sin(k:r — wt + <15), the second being shifted from the ﬁrst by 3‘ +51 = Um [25M(k)<wt) 05 g 1
a constant phase 4). From the principle of ' superposition, the resultant wave has an = (23%“5 g 3 5"“(l‘x‘wt )
amplitude (b) 2ym obs a5
0 gm c08(¢/2) (d) ym cos d) (e) none of these 2. In the following series of resonant frequencies in an oscillating system,
one frequency (lower than 400 Hz) is missing: 150, 225, 300, 375 Hz. M359 x .. 75 H1 : x a a; a. 2X : g x 1
What is the missing frequency? (a) 50 Hz b 75 Hz (0) 100 Hz (d) 395 Hz (e) Can’t tell without knowing the details of the oscillating system. 3. A tuning fork with a frequency of 440 Hz is played simultaneously with a
fork with a frequency of 437 Hz. How many beats will be heard over a period
of 10 seconds? ' (a) 3 (b) 6 (c) 10 (e) not enough information 3 a»; ”CB =3Hz=3iwm ”
ir—a
l
#3
Si/
N l' pt] walokc 5° (\ When a tennis racket strikes a tennis ball, the
racket begins to vibrate. There is a set of se
lected frequencies at which the racket will tend
to vibrate. Each frequency in the set is charac—
terized by. a particular standing wave pattern.
The diagrams on the right show the three of
the more common standing wave patterns for Pattern A Pattern B Pattgrn C — )2
the vibrations of a tennis racket. Answer the L ’ Z; 37? ) :31"
following three questions. }\ _: g, L 1, 4L 4'
3 __ 4. Rank the wavelengths of patterns A, B, C, longest ﬁrst. 4
(a) A=B, C (b) A, B=C I (c) A, B, C l (d) C, B, A A 6 C
(e) none of these qr I: , 21’— , if
5. Rank the frequencies of patterns A, B, C, highest ﬁrst. 5” :' "ﬁ' 3’ 4L ‘1’— 41—» (a) A=B,C (b) A, B=C (c) A, B,C ((d)c,B,A[ (e) none of these 6. When the racket vibrates as in pattern A, its frequency of vibration is
approximately 30 Hz. Determine the frequencies of vibration of the racket
when it vibrates as in pattern B and pattern C. DC ; 53 ) 355A I ‘f‘l‘A (a) f3 = 30 Hz, f0 = 90 Hz (b) f3 = 90 Hz, f = 120 Hz
(c)f3=90Hz,fo=150 Hz . B=90Hz,fc=90Hz
(e) not enough information ‘ 7. The ”buzz” of a mosquito produces an intensity having a 40dB rating. How many times more intense is the sound of normal conversation if it has
an intensity rating of 60dB? (a) 2 (b) 20 (d) 400 (e) none of these I
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60 40 : 2.0 ‘LB 3 I+o Two speakers are arranged so that sound waves
with the same frequency are produced and radi
ate through the room. An interference pattern
is created (as represented in the diagram at the
right). The thick lines in the diagram represent
wave crests and the thin lines represent wave
troughs. Use the diagram to answer the next
two questions. 8. How many of the six labeled points represent
anti—nodes? (a)1 (c)3 (d)4 (e)6 9. At which point(s) would constructive interference occur? (iii: (a B onl (b) A, B, and C (c) D, E, and F
(d) A and B , (e) Not enough information A $ 3 10. Which of the following is NOT true?) (a) A sound wave is a pressure wave; like all waves, it is able to bend into
the regions of space behind obstacles. V (b) In an ideal gas, collisions between molecules and the container wall are
perfectly elastic (that is, no energy is gained or lost during the collision). (c) In an ideal gas, the average kinetic energy of a molecule is fkT / 2, where
the number of degrees of freedom f depends on temperature. (T is the ab
solute temperature and k is the Boltzmann constant.) /
((1) Robert Boyle discovered that at a ﬁxed temperature, the pressure of an ideal gas is inversely proportional to its volume.
' 1/ (e) all of these are true a rectangular valley of depth 2 units and
width d. The wave travels to the right.
Waves 2, 3, 4 are similar waves with al
4 .
the same heights, depths and widths, and “‘ 4' ‘— 2.
travel to the left and through wave 1. a. =1 4 l A l
(3) (4) Answer the following three questions: A
In the ﬁgure, wave 1 consists of a rectangu 4 A —> <—
lar peak of height 4 units and width d, and A 7. A 7.
(1) (2) 11. With which choice will the interference produce, for an instant, the deepest valley? (a) 1 and 2 (b) 1 and 3 (c) 1 and 4 ((1) none of these 12. With which choice will the interference produce, for an instant, a ﬂat
line? _ .——p (a) 1 and 2 (b) 1 and 3 (c) 1 and 4 (d) none of these 13. With which choice will the interference produce, for an instant, a level
p_e_a—l§ 2d wide? (a) 1 and 2 l (b) 1 and 3 R (c) 1 and 4 (d) none of these 14. Compute the RMS speed of an H2 molecule at 0 °C if the RMS speed
of an 02 molecule at this temperature is 500 m/s. The answer is closest to: 316i”
(a) 500 m/s (b) 2000 m/s (c) 125 m/s (d) 5000 m/s ”ms ‘ M
(d) none of thes = :61—
M 15. Assume that the volume of a balloon ﬁlled with H2 is 1.00 L at 25
°C. Calculate the volume of the balloon when it is cooled to 78 °C in a
lowtemperature bath made by adding dry ice to acetone. (a) 3.12 L (c) 1.54 L (d) 312 L
(d) none of these 25* C : 25 +L75 ‘ 233., I“ 1 ~ (“5+ 33°C ‘ ~7‘6’r173 ' ”5 K T
v vi  1:» V "0‘“ L"
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 Winter '07
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