132Sp07mt2s - NAME_—KEY_— WebCT ID Cal Poly University...

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Unformatted text preview: NAME: _—KEY___— WebCT ID: Cal Poly University Pomona Physics Department PHY 132-01 50-minute 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 ” i-r—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 40-dB rating. How many times more intense is the sound of normal conversation if it has an intensity rating of 60-dB? (a) 2 (b) 20 (d) 400 (e) none of these I ma #:er 90153 31:” I5 0 O 2.». go <49 :10 {203 Ice“ it? if: z 3;:[909 £0 » :10 [0° 6 u 6: - Iév . loo 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 low-temperature 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" 1': LIL ’LQY ...
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