Physics 125 Practice Exam #5 Chapters 16-17 Professor Siegel Name: Lab Day: 1. A periodic wave is produced on a stretched string. Which one of the following properties is not related to the speed of the wave? A) frequency B) amplitude C) period D) wavelength E) tension in the string 2. A periodic wave travels along a stretched string in the direction shown by the arrow. The sketch shows a snapshot of the pulse at a certain instant. Points A, B, and C are on the string. Which entry in the table below correctly describes how particles of string between A and B and between B and C are moving? between A and B between B and C A) down down B) up down C) left right D) up up E) down up Page 1
3. The speed of sound in a certain metal block is 2.00 10 3 m/s. The graph shows the amplitude (in meters) of a wave traveling through the block versus time (in milliseconds). What is the wavelength of this wave? A) 0.5 m B) 1.5 m C) 3.0 m D) 4.0 m E) 6.0 m 4. Two canoes are 10 m apart on a lake. Each bobs up and down with a period of 8.0 seconds. When one canoe is at its highest point, the other canoe is at its lowest point. Both canoes are always within a single cycle of the waves. Determine the speed of the waves. A) 2.5 m/s B) 1.3 m/s C) 5.0 m/s D) 0.65 m/s E) 0.75 m/s 5. What is the wavelength of a wave with a speed of 9.0 m/s and a period of 0.33 s? A) 0.33 m B) 1.5 m C) 3.0 m D) 13 m E) 27 m Page 2
Use the following to answer questions 6-9: The displacement of a vibrating string versus position along the string is shown in the figure. The periodic waves have a speed of 10.0 cm/s. A and B are two points on the string. 6. What is the amplitude of the wave? A) 2 mm B) 4 mm C) 8 mm D) 12 mm E) 16 mm 7. What is the wavelength of the wave? A) 3.0 cm B) 6.0 cm C) 9.0 cm D) 12 cm E) 15 cm 8. What is the frequency of the wave? A) 0.60 Hz B) 0.90 Hz C) 1.1 Hz D) 1.3 Hz E) 1.7 Hz Page 3
9. What is the difference in phase between the points A and B? A) (π/4) radians B) (π/2) radians C) π radians D) (3π/4) radians E) 2π radians 10. The tension in a taut rope is increased by a factor of 9. How does the speed of wave pulses on the rope change, if at all? A) The speed remains the same. B) The speed is reduced by a factor of 3. C) The speed is reduced by a factor of 9. D) The speed is increased by a factor of 3. E) The speed is increased by a factor of 9. 11. A certain string on a piano is tuned to produce middle C (f = 261.63 Hz) by carefully adjusting the tension in the string. For a fixed wavelength, what is the frequency when this tension is tripled? A) 87.21 Hz B) 151.05 Hz C) 370.00 Hz D) 453.16 Hz E) 784.89 Hz 12. How far must one stand from a 5-mW point sound source if the intensity at that location is at the hearing threshold? Assume the sound waves travel to the listener without being disturbed. A) 500 m B) 1 km C) 2 km D) 4 km E) 20 km 13. The decibel level of a jackhammer is 125 db relative to the threshold of hearing. Determine the sound intensity produced by the jackhammer. A) 1.0 W/m 2 B) 3.2 W/m 2 C) 4.8 W/m 2 D) 12 W/m 2 E) 88 W/m 2 Page 4
14. A car moving at 35 m/s approaches a stationary whistle that emits a 220 Hz sound. The speed of sound is 343 m/s. What is the frequency of sound heard by the driver of the car? A) 198 Hz B) 220 Hz C) 245 Hz D) 282 Hz E) 340 Hz 15. Two motorcycles are traveling in opposite directions at the same speed when one of the cyclists blasts his horn, which has frequency of 544 Hz. The other cyclist hears the frequency as 522 Hz. If the speed of sound in air is 344 m/s, what is the speed of the motorcycles? A) 5.90 m/s B) 7.24 m/s C) 8.19 m/s D) 10.0 m/s E) 11.6 m/s 16. A pebble is dropped in a lake; and it produces ripples with a frequency of 0.50 Hz. When should a second pebble be dropped at the same place to produce destructive interference? A) 0.50 s after the first B) 0.75 s after the first C) 1.0 s after the first D) 1.5 s after the first E) 2.0 s after the first 17. Two loudspeakers, A and B, are separated by a distance of 2.0 m. The speakers emit sound waves at a frequency of 680 Hz that are exactly out of phase. The speed of sound is 343 m/s. How far from speaker A along the +x axis will a point of constructive interference occur? A) 0.25 m B) 0.30 m C) 0.46 m D) 0.88 m E) 0.98 m Page 5
18. Water waves approach an aperture. The resulting patterns are shown for two different cases, A and B, in which the wavelength and aperture size are varied. Which one of the following statements concerning these cases is true? A) Neither figure shows diffraction. In both cases, the wavelength is much smaller than the aperture. B) Diffraction occurs in A, but not in B because the wavelength in A is much smaller than the aperture. C) Diffraction occurs in B, but not in A because the wavelength in B is much smaller than the aperture. D) Both figures show diffraction. In both cases, the wavelengths are approximately the same size as the aperture. E) Diffraction occurs in B, but not in A because the wavelength in B is approximately the same size as the aperture. 19. A speaker is designed for wide dispersion for a high frequency sound. What should the diameter of the circular opening be for a speaker where the desired diffraction angle is 11 and a 9100 Hz sound is generated? The speed of sound is 343 m/s. A) 0.039 m B) 0.077 m C) 0.24 m D) 0.13 m E) 0.048 m 20. Which one of the following superpositions will result in beats? A) the superposition of waves that travel with different speeds B) the superposition of identical waves that travel in the same direction C) the superposition of identical waves that travel in opposite directions D) the superposition of waves that are identical except for slightly different amplitudes E) the superposition of waves that are identical except for slightly different frequencies Page 6
21. Two timpani (tunable drums) are played at the same time. One is correctly tuned so that when it is struck, sound is produced that has a wavelength of 2.20 m. The second produces sound with a wavelength of 2.10 m. If the speed of sound is 343 m/s, what beat frequency is heard? A) 7 beats/s B) 9 beats/s C) 11 beats/s D) 13 beats/s E) 15 beats/s 22. Which one of the following statements is true concerning the points on a string that sustain a standing wave pattern? A) All points vibrate with the same energy. B) All points undergo the same displacements. C) All points vibrate with different frequencies. D) All points vibrate with different amplitudes. E) All points undergo motion that is purely longitudinal. 23. A 4.00-m long string, clamped at both ends, vibrates at 2.00 10 2 Hz. If the string resonates in six segments, what is the speed of transverse waves on the string? A) 100 m/s B) 133 m/s C) 267 m/s D) 328 m/s E) 400 m/s Use the following to answer question 24: Vibrations with frequency 6.00 10 2 Hz are established on a 1.33-m length of string that is clamped at both ends. The speed of waves on the string is 4.00 10 2 m/s. 24. How many antinodes are observed for the resulting standing wave pattern? A) 2 B) 3 C) 4 D) 5 E) 6 Page 7
Use the following to answer question 25: The figures show standing waves of sound in six organ pipes of the same length. Each pipe has one end open and the other end closed. Note: some of the figures show situations that are not possible. 25. Which of the figures do not illustrate possible resonant situations? A) 1 and 4 B) 2 and 3 C) 4 and 5 D) 5 and 6 E) 4, 5, and 6 Page 8
Answer Key 1. B 2. B 3. D 4. A 5. C 6. B 7. B 8. E 9. C 10. D 11. D 12. E 13. B 14. C 15. B 16. C 17. D 18. E 19. C 20. E 21. A 22. D 23. C 24. C 25. D Page 9