MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

Transcription

1 Exam Name MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) A 660-Hz tone has an intensity level of 54 db. The velocity of sound in air is 345 m/s. The bulk modulus of air is 142 kpa. The pressure amplitude of the sound waves, in SI units, is closest to: A) B) C) D) E) ) 2) A 380-Hz tone has an intensity level of 64 db. The velocity of sound in air is 345 m/s. The bulk modulus of air is 142 kpa. The displacement amplitude of the sound waves, in SI units, is closest to: A) B) C) D) E) ) 3) A 860-Hz tone has an intensity level of 71 db. The velocity of sound in air is 345 m/s. The bulk modulus of air is 142 kpa. A 1548-Hz tone has the same displacement amplitude as does the 860-Hz tone. The difference in the intensity level of the 1548-Hz tone relative to that of the 860 Hz tone, in db, is closest to: A) -5.1 B) 5.1 C) 2.6 D) -2.6 E) zero 3) 4) A 710-Hz tone has an intensity level of 23 db. The velocity of sound in air is 345 m/s. The bulk modulus of air is 142 kpa. An 1122-Hz tone has the same pressure amplitude as does the 710-Hz tone. The difference in the intensity level, of the 1122 Hz tone relative to that of the 710-Hz tone, in db, is closest to: A) zero B) 2.0 C) 4.0 D) -2.0 E) ) 5) The howler monkey is the loudest land animal and can be heard up to a distance of 5.0 km. Assume the acoustic output of a howler to be uniform in all directions. The acoustic power emitted by the howler, in mw, is closest to: A) 11 B) 0.11 C) 0.32 D) 1.1 E) 3.2 5) 6) The howler monkey is the loudest land animal and can be heard up to a distance of 8.0 km. Assume the acoustic output of a howler to be uniform in all directions. The distance at which the intensity level of a howler's call is 28 db, in SI units, is closest to: A) 540 B) 380 C) 320 D) 480 E) 640 6) 1

2 7) The howler monkey is the loudest land animal and can be heard up to a distance of 4.5 km. Assume the acoustic output of a howler to be uniform in all directions. A chorus of five howlers call at the same time. The largest distance at which the chorus can be heard, in km, is closest to: A) 18 B) 6.7 C) 10 D) 23 E) 14 7) 8) The howler monkey is the loudest land animal and can be heard up to a distance of 8.4 km. Assume the acoustic output of a howler to be uniform in all directions. A juvenile howler monkey has an acoustic output of 50 µw. The ratio of the acoustic intensity produced by the juvenile howler to the reference intensity I o, at a distance of 460 m, is closest to: A) 19 B) 38 C) 28 D) 50 E) 13 9) An enclosed chamber with sound absorbing walls has a 2.0 m 1.0 m opening for an outside window. A loudspeaker is located outdoors, 74 m away and facing the window. The intensity level of the sound entering the window space from the loudspeaker is 24 db. Assume the acoustic output of the loudspeaker is uniform in all directions and that acoustic energy incident upon the ground is completely absorbed. The acoustic power entering through the window space, in µw, is closest to: A) B) C) D) E) ) 9) 10) An enclosed chamber with sound absorbing walls has a 2.0 m 1.0 m opening for an outside window. A loudspeaker is located outdoors, 90 m away and facing the window. The intensity level of the sound entering the window space from the loudspeaker is 27 db. Assume the acoustic output of the loudspeaker is uniform in all directions and that acoustic energy incident upon the ground is completely absorbed. The sound intensity at a point midway between the loudspeaker and the window, in SI units, is closest to: A) B) C) D) E) ) 11) An enclosed chamber with sound absorbing walls has a 2.0 m 1.0 m opening for an outside window. A loudspeaker is located outdoors, 78 m away and facing the window. The intensity level of the sound entering the window space from the loudspeaker is 41 db. Assume the acoustic output of the loudspeaker is uniform in all directions and that acoustic energy incident upon the ground is completely absorbed. The acoustic output of the loudspeaker, in SI units, is closest to: A) B) C) D) E) ) 12) A glass window is installed in the window space and the intensity level of the sound entering through the window is reduced from 84 db to 71 db. The factor, by which the acoustic power entering the chamber is reduced by the glass window, is closest to: A) B) C) D) E) ) 2

3 13) Consider the waves on a vibrating guitar string and the sound waves the guitar produces in the surrounding air. The string waves and the sound waves have the same A) amplitude. B) wavelength. C) frequency. D) velocity. E) More than one of the above is true. 13) 14) Which one of the following statements is true? A) If the intensity of sound A is twice the intensity of sound B, then the intensity level (in decibels) of A is twice the intensity level of B. B) If two different sound waves have the same displacement amplitude, then they must have the same intensity. C) If two sound waves have the same intensity level (in decibels), they must have the same intensity. D) If two different sound waves have the same displacement amplitude, then they must have the same intensity level (in decibels). E) If the intensity level (in decibels) of sound A is twice the intensity level of sound B, then the intensity of A is twice the intensity of B. 14) 15) Which of the following increases when a sound becomes louder? A) Amplitude B) Phase C) Velocity D) Wavelength E) Period 15) 16) What is the intensity level in decibels of a sound whose intensity is 10-7 W/m 2? A) 20 db B) 50 db C) 60 db D) 30 db E) 40 db 16) 17) An open pipe, 0.46 m long, vibrates in the second overtone with a frequency of 1200 Hz. In this situation, the distance from the center of the pipe to the nearest antinode, in cm, is closest to: A) 12 B) 3.8 C) 7.7 D) 15 E) zero 17) 18) An open pipe, 0.64 m long, vibrates in the second overtone with a frequency of 848 Hz. In this situation, the speed of sound in air, in SI units, is closest to: A) 350 B) 344 C) 368 D) 356 E) ) 19) An open pipe, 0.28 m long, vibrates in the second overtone with a frequency of 1900 Hz. In this situation, the fundamental frequency of the pipe, in SI units, is closest to: A) 482 B) 634 C) 1520 D) 951 E) ) 20) An open pipe, 0.62 m long, vibrates in the second overtone with a frequency of 888 Hz. In this situation, the length of the shortest stopped pipe, which has the same resonant frequency as the open pipe in the second overtone, in cm, is closest to: A) 10 B) 12 C) 21 D) 5.2 E) 31 20) 3

4 Situation 16.1 A standing wave of the third overtone is induced in a stopped pipe, 1.2 m long. The speed of sound is 340 m/s. 21) In Situation 16.1, the number of antinodes in the standing wave pattern is: A) 3 B) 6 C) 5 D) 4 E) 7 21) 22) In Situation 16.1, the frequency of the sound produced by the pipe, in SI units, is closest to: A) 210 B) 350 C) 430 D) 280 E) ) 23) Three tuning forks are available. Fork A produces a 440 Hz tone. The other forks are marked X and Y. The frequency of fork Y is less than the frequency of fork X. When forks A and X are sounded together, a beat frequency of 4 Hz is heard. For forks A and Y, the beat frequency is 7 Hz. For forks X and Y, the beat frequency is 3 Hz. The frequencies of forks X and Y, respectively, in SI units, are closest to: A) 436 and 433 B) 444 and 447 C) 447 and 444 D) 436 and 447 E) 444 and ) Situation 16.2 A stopped wire, 0.90 m long, resonates with a tone whose wavelength is 0.72 m. 24) In Situation 16.2, the number of the harmonic for this resonant wavelength is: A) 3 B) 5 C) 6 D) 2 E) 4 24) 25) In Situation 16.2, the distance between a node and an adjacent antinode in the standing wave pattern in the pipe, in SI units, is closest to: A) 0.18 B) 0.36 C) 0.45 D) 0.27 E) ) 26) In Situation 16.2, the wavelength of the next higher overtone in this pipe, in SI units, is closest to: A) 0.51 B) 0.58 C) 0.40 D) 0.45 E) ) 27) In Situation 16.2, the overtone number of this normal mode is: A) 4 B) 5 C) 2 D) 3 E) 6 27) 28) In Situation 16.2, the frequency of this normal mode, in SI units, is closest to: A) 220 B) 330 C) 380 D) 270 E) ) 29) Two loudspeakers placed 6.0 m apart are driven in phase by an audio oscillator, whose frequency range is 1399 Hz to 1812 Hz. A point P is located 5.1 m from one loudspeaker and 3.6 m from the other. The speed of sound is 344 m/s. The frequency produced by the oscillator, for which constructive interference of sound occurs at point P, in SI units, is closest to: A) 1663 B) 1605 C) 1777 D) 1720 E) ) 4

5 30) Two loudspeakers placed 6.0 m apart are driven in phase by an audio oscillator, whose frequency range is 1350 Hz to 1826 Hz. A point P is located 4.9 m from one loudspeaker and 3.6 m from the other. The speed of sound is 344 m/s. The frequency produced by the oscillator, for which destructive interference occurs at point P, in SI units, is closest to: A) 1799 B) 1694 C) 1720 D) 1746 E) ) 31) Which of the following is an accurate statement? A) Standing waves can be set up in a pipe closed on both ends, but not in one with one end open and one end closed. B) The fundamental frequency of an organ pipe is determined primarily by the pipe diameter. C) The open end of a pipe is a pressure antinode for standing waves. D) Displacement nodes and pressure antinodes occur at the same place in an organ pipe. E) Standing sound waves can be set up in a pipe open on one end, but not on one open on both ends. 31) 32) An organ pipe open at both ends has two successive harmonics with frequencies of 210 Hz and 240 Hz. What is the length of the pipe? The speed of sound is 345 m/s in air. A) 5.25 m B) 2.76 m C) 4.90 m D) 5.75 m E) 3.62 m 32) Situation 16.3 Two loudspeakers S1 and S2, placed 5.0 m apart, are driven in phase by an audio oscillator. A boy stands at point P, which is 12.0 m from S1 and 13.0 m from S2. A right triangle is formed by S1, S2, and P. The wave from S2 arrives at point P 2.00 periods later than the wave from S1. The speed of sound is 350 m/s. 33) In Situation 16.3, the frequency of the oscillator, in SI units, is closest to: A) 500 B) 700 C) 1400 D) 1000 E) ) 34) In Situation 16.3, the boy walks directly away from S1, along the line through P, until destructive interference occurs. At that point, the wave from S2 arrives 1.50 periods later than the wave from S1. The distance of this point from S1, in SI units, is closest to: A) 14.3 B) 16.3 C) 15.3 D) 15.8 E) ) Situation 16.4 A car on a road parallel to and right next to a railroad track is approaching a train. The car is traveling eastward at 30.0 m/s while the train is going westward at 50.0 m/s. There is no wind, and the speed of sound is 344 m/s. The car honks its horn at a frequency of 1.00 khz as the train toots its whistle at a frequency of 1.50 khz. 35) In Situation 16.4, the frequency that the car's driver hears from the train's whistle is closest to: A) 1.18 khz B) 1.15 khz C) 1.95 khz D) 1.20 khz E) 1.91 khz 35) 36) In Situation 16.4, the wavelength of the sound from the train's whistle, as measured by the driver of the car, is closest to: A) m B) m C) m D) m E) m 36) 5

6 37) In Situation 16.4, the frequency that a person riding on the train measures for the sound from the car's horn is closest to: A) khz B) 1.05 khz C) khz D) 1.25 khz E) 3.79 khz 37) 38) In Situation 16.4, the wavelength of the sound from the car's horn, as measured by a person riding in the train, is closest to: A) m B) m C) m D) m E) m 38) 39) In Situation 16.4, the driver of the car hears the sound of her horn reflected back toward her from the front of the moving train. The frequency she measures for this reflected sound is closest to: A) 1.19 khz B) 1.19 khz C) 1.19 khz D) 1.19 khz E) 1.19 khz 39) 40) In Situation 16.4, the car and train eventually pass each other and continue traveling away from each other. In this case, the frequency of the sound that the driver of the car hears from the train s whistle is closest to: A) 1.42 khz B) 1.91 khz C) 1.22kHz D) 1.60 khz E) 1.20 khz 40) Situation 16.5 A carousel, 5.0 m in radius, has a pair of 600-Hz sirens, mounted on posts at opposite ends of a diameter. The carousel rotates with an angular velocity of 0.80 rad/s. A stationary listener is located at a distance from the carousel. The speed of sound is 350 m/s. 41) In Situation 16.5, the longest wavelength reaching the listener from the sirens, in cm, is closest to: A) 59.0 B) 58.3 C) 57.0 D) 57.7 E) ) 42) In Situation 16.5, the highest siren frequency heard by the listener, in SI units, is closest to: A) 609 B) 605 C) 611 D) 603 E) ) 43) In Situation 16.5, the maximum beat frequency of the sirens at the position of the listener, in SI units, is closest to: A) 12 B) 14 C) 8 D) 10 E) 6 43) 44) In Situation 16.5, the listener mounts a bicycle and rides directly away from the carousel with a speed of 4.5 m/s. The highest siren frequency heard by the listener, in SI units, is given by: A) 345.5/ B) 354.5/ C) 354.0/ D) 354.5/ E) 345.5/ ) 45) A jet aircraft, in level flight at constant speed, is observed directly overhead. A sonic boom is heard 12.0 s later, at which time the line of sight to the aircraft forms a 54 angle with respect to the horizontal. The speed of sound is 325 m/s. The Mach number for the aircraft is closest to: A) 1.7 B) 1.8 C) 2.0 D) 2.1 E) ) 6

7 46) A jet aircraft, in level flight at constant speed, is observed directly over head. A sonic boom is heard 9.0 s later, at which time the line of sight to the aircraft forms a 53 angle with respect to the horizontal. The speed of sound is 325 m/s. The altitude of the aircraft, in SI units, is closest to: A) 6000 B) 4900 C) 3700 D) 1800 E) ) 47) The reason a decibel scale is used to measure sound intensity level is that A) decibels are dimensionless. B) the intensity levels usually encountered are too small to be expressed in the usual exponential notation. C) the ear is sensitive over such a broad range of intensities. D) the intensity levels usually encountered are too large to be expressed in the usual exponential notation. E) the energy in a sound wave varies exponentially with the amplitude of the wave. 47) Figure ) In Fig are some wavefronts emitted by a source of sound S. This picture can help us to understand A) the phenomenon of beats. B) why a sound grows quieter as we move away from the source. C) how sonar works. D) why the siren on a police car changes its pitch as it races past us. E) why it is that our hearing is best near 3000 Hz. 48) 49) A person is hearing two sound waves simultaneously. One has a period of 1.50 ms and the other one a period of 1.54 ms. The beat due to these two waves has a period closest to: A) ms B) 57.8 ms C) 3.04 ms D) 329 ms E) 1.52 ms 49) 50) The speed of sound in steel is 5000 m/s. What is the wavelength of a sound wave of frequency 270 Hz in steel? A) 2.95 m B) m C) m D) 5.89 m E) 18.5 m 50) 7

8 51) The speed of sound in an alcohol, at a temperature of 20 C, is 1240 m/s. The density of the alcohol at that temperature is 830 kg/m 3. The bulk modulus of the alcohol, at a temperature of 20 C, in MPa, is closest to: A) 1470 B) 1530 C) 1340 D) 1280 E) ) A pipe, 20 m long and 10.0 cm in diameter contains olive oil. The density of the olive oil is 890 kg/m 3 and the bulk modulus is Pa. A 53.4-Hz longitudinal wave is transmitted in the oil. The time for the wave to travel the length of the pipe in the oil, in ms, is closest to: A) 17 B) 13 C) 15 D) 14 E) 12 53) A pipe, 40 m long and 10.0 cm in diameter contains olive oil. The density of the olive oil is 865 kg/m 3 and the bulk modulus is Pa. A 980-Hz longitudinal wave is transmitted in the oil. The wavelength of the longitudinal wave in the oil, in SI units, is closest to: A) 1.5 B) 1.4 C) 1.7 D) 1.2 E) ) A pipe, 60 m long and 10.0 cm in diameter contains olive oil. The density of the olive oil is 933 kg/m 3 and the bulk modulus is Pa. A 980-Hz longitudinal wave of amplitude 4.0 mm is transmitted in the oil. The intensity of the wave, is closest to: A) B) C) D) E) ) 52) 53) 54) 55) A metal bar 14.0 m long has a density of 5800 kg/m 3 and a diameter of 6 cm. Longitudinal sound waves take s to travel the length of the bar. What is Young's modulus for this material? A) Pa B) Pa C) Pa D) Pa E) Pa 55) Situation 16.6 A uniform bar of metal, 0.40 m long, with a diameter of 2.0 cm, has a mass of 1.1 kg. A 1.5-MHz longitudinal wave is propagated along the length of the bar. A wave compression traverses the length of the bar in 0.12 ms. 56) In Situation 16.6, the wavelength of the longitudinal wave in the metal, in mm, is closest to: A) 2.6 B) 2.2 C) 3.8 D) 3.0 E) ) 57) In Situation 16.6, the value of Young's modulus for the metal, in GPa (G = giga = 10 9 ), is closest to: A) 97 B) 73 C) 79 D) 85 E) 91 57) 58) The molecular mass of helium is kg/mol and the adiabatic constant is The speed of sound in helium gas, taken as an ideal gas, at a temperature of 290 K and a pressure of 80 kpa, in SI units, is closest to: A) 1100 B) 1200 C) 900 D) 1000 E) ) 8

9 59) A star is moving toward earth at one-third the speed of light and is emitting light of frequency Hz. The frequency of light measured by an observer on earth is closest to: A) Hz B) Hz C) Hz D) Hz E) Hz 59) 60) Two identical loudspeakers that are 5.00 m apart and face toward each other are driven in phase by the same oscillator at a frequency of 875 Hz. You are standing midway between the speakers, and the speed of sound in the room is 344 m/s. The minimum distance you can walk toward either speaker in order to hear a minimum of sound is closest to: A) m B) m C) m D) m E) m 60) 61) At a distance of 2.00 m from a point source of sound, the intensity level is 80.0 db. At a distance of 4.00 m from this source, the intensity level will be closest to: A) 74.0 db B) 40.0 db C) 60.0 db D) 77.0 db E) 20.0 db 61) 62) Which one of the following statements is true? A) Both the intensity level (in db) and the sound intensity can never be negative. B) Both the intensity level (in db) and the sound intensity can be negative. C) Both intensity level (in db) and sound intensity obey inverse-square distance laws. D) The sound intensity can never be negative, but the intensity level (in db) can be negative. E) The intensity level (in db) obeys an inverse-square distance law, but the sound intensity does not. 62) 63) Sound takes 10.0 ms to travel across a certain experimental enclosure. If the absolute temperature in this enclosure is doubled, the time for sound to travel across it will be closest to: A) 2.50 ms B) 14.1 ms C) 7.07 ms D) 20.0 ms E) 5.00 ms 63) 64) Under certain conditions the speed of sound in air is 340 m/s. If the temperature were to rise by 1.00%, what would the speed of sound then be? A) 339 m/s B) 342 m/s C) 338 m/s D) 341 m/s E) 340 m/s 64) SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 65) A certain source of sound waves radiates uniformly in all directions. At a distance of 20 m from the source the intensity level is 51 db. What is the total acoustic power output of the source, in watts? (Note: The reference intensity I o is W/m 2.) 65) 9

10 Figure ) In Fig. 16.2, a man is traveling on a bicycle at 18 m/s along a straight road that runs parallel to some railroad tracks. He hears the whistle of a train that is behind him, as shown in the sketch. The frequency emitted by the train is 840 Hz, but the frequency the man hears is 778 Hz. Take the velocity of sound to be 340 Hz. a) What frequency is heard by a stationary observer located between the train and the bicycle? b) What is the speed of the train, and is the train traveling away from or toward the bicycle? 66) 67) Two violists are tuning their A-strings, for which the fundamental frequency is 440 Hz when properly tuned. When both play the A-note, 6.9 beats per second are heard. By what fractional amount must the player of the viola with the lower frequency increase the tension in his string to make its frequency identical to that of the other viola? Assume that the other viola is already properly tuned. Express your answer in percent (%). 67) 68) What must be the length of an organ pipe that is open at one end and closed at the other if its fundamental frequency is to be 5 times that of a pipe that is 2.10 meters long and open at both ends? 68) Figure ) In Fig. 16.3, two identical loudspeakers, A and B, driven by the same amplifier, are separated by 2.00 m and produce sound waves of the same frequency. A small microphone is placed at point C, 3.00 m from speaker A along the line perpendicular to the line connecting the two speakers. At this point destructive interference occurs. If the microphone is now moved along this line to point D, 4.50 m from speaker A, constructive interference occurs. Find the frequency of the sound waves. The speed of sound is 344 m/s. Assume that there are no other points between C and D where interference occurs. 69) 10

11 70) A police siren produces a sound level of 81.0 db with a pressure amplitude of 0.75 Pa. Find the new intensity level if the pressure amplitude changes to 2.48 Pa. 70) 71) Two police cars have identical sirens that produce a frequency of 570 Hz. A stationary listener is standing between two cars. One car is parked and the other is approaching the listener and both have their sirens on. The listener notices 9.7 beats per second. Find the speed of the approaching police car. (The speed of sound is 340 m/s.) 71) 72) Find the ratio of the speed of sound in nitrogen gas to that of air at room temperature, t = 20.0 C. The molecular mass of nitrogen is g/mol and! is The molecular mass of air is 28.8 g/mol and! is ) 73) A string 40.0 cm long of mass 8.50 g is fixed at both ends and is under a tension of 425 N. When this string is vibrating in its third overtone, you observe that it causes a nearby pipe, open at both ends, to resonate in its third harmonic. The speed of sound in the room is 344 m/s. (a) How long is the pipe? (b) What is the fundamental frequency of the pipe? 73) 74) A sound wave of wavelength 26.0 cm in air has an intensity level of 45.0 db. By how many pascals does the pressure of this wave vary above and below the ambient air pressure? The reference intensity is W/m 2, the speed of sound in the room is 344 m/s, and the density of the air is 1.20 kg/m 2. 74) 11

12 Answer Key Testname: UNTITLED3 1) B 2) C 3) B 4) A 5) C 6) C 7) C 8) A 9) C 10) C 11) E 12) D 13) C 14) C 15) A 16) B 17) C 18) E 19) A 20) A 21) D 22) E 23) C 24) B 25) A 26) A 27) C 28) D 29) B 30) C 31) D 32) D 33) B 34) B 35) E 36) D 37) D 38) E 39) D 40) E 41) A 42) E 43) B 44) A 45) E 46) B 47) C 48) D 49) B 12

13 Answer Key Testname: UNTITLED3 50) E 51) D 52) A 53) A 54) B 55) D 56) B 57) A 58) D 59) A 60) A 61) A 62) E 63) C 64) B 65) watts 66) a) 821 Hz b) 7.8 m/s, away from the bicycle 67) 3.1 % 68) meters 69) 950 Hz 70) 91.4 db 71) 5.7 m/s 72) 1.01 times as fast 73) (a) m (b) 236 Hz 74) Pa 13