Physics: Principle and Applications, 7E (Giancoli)

Physics: Principle and Applications, 7e (Giancoli) Chapter 12 Sound

12.1 Conceptual Questions

1) Seven seconds after a brilliant flash of lightning, thunder shakes the house. Approximately how far was the lightning strike from the house? A) much closer than one kilometer B) about one kilometer away C) about two kilometers away D) much farther away than two kilometers E) It is impossible to say. Answer: C Var: 1

2) What characteristics of a sound wave are related to the "pitch" of a musical note? (There could be more than one correct choice.) A) amplitude B) wavelength C) frequency D) period Answer: B, C, D Var: 1

3) Sound A has a high pitch and sound B has a low pitch. Which of the following statements about these two sounds are correct? (There could be more than one correct choice.) A) The wavelength of A is longer than the wavelength of B. B) The period of A is shorter than the period of B. C) The frequency of A is greater than the frequency of B. D) Sound B travels faster than sound B through air. E) The amplitude of A is larger than the amplitude of B. Answer: B, C Var: 1

4) You double your distance from a sound source that is radiating equally in all directions. What happens to the intensity of the sound? It reduces to A) one-half its original value. B) one-fourth its original value. C) one-sixteenth its original value. D) none of the above Answer: B Var: 1

1 Copyright © 2014 Pearson Education, Inc. 5) Suppose that a sound source is emitting waves uniformly in all directions. If you move to a point twice as far away from the source, the frequency of the sound will be A) unchanged. B) half as great. C) one-fourth as great. D) twice as great. Answer: A Var: 1

6) An organ pipe of length L that is open at one end resonates in its third harmonic with a wavelength of 2L/3. Is the other end of the pipe closed or open? A) closed B) open C) We cannot tell from the information provided. Answer: B Var: 1

7) In a resonating pipe that is open at both ends, there A) are displacement nodes at each end. B) are displacement antinodes at each end. C) is a displacement node at one end and a displacement antinode at the other end. D) None of the above choices are correct. Answer: B Var: 1

8) In a resonating pipe that is open at one end and closed at the other end, there A) are displacement nodes at each end. B) are displacement antinodes at each end. C) is a displacement node at the open end and a displacement antinode at the closed end. D) is a displacement node at the closed end and a displacement antinode at the open end. Answer: D Var: 1

9) The lowest tone to resonate in pipe of length L that is open at both ends is 200 Hz. Which one of the following frequencies will not resonate in the same pipe? A) 200 Hz B) 400 Hz C) 600 Hz D) 800 Hz E) 900 Hz Answer: E Var: 1

2 Copyright © 2014 Pearson Education, Inc. 10) The lowest tone to resonate in a pipe of length L that is closed at one end but open at the other end is 200 Hz. Which one of the following frequencies will not resonate in that pipe? A) 200 Hz B) 400 Hz C) 600 Hz D) 1000 Hz E) 1400 Hz Answer: B Var: 1

11) Consider the standing wave on a guitar string and the sound wave generated by the string as a result of this vibration. What do these two waves have in common? (There may be more than one correct choice.) A) They have the same wavelength. B) They have the same speed. C) They have the same frequency. D) They have the same amplitude. E) They have the same period. Answer: C, E Var: 1

12) Consider a pipe of length L that is open at both ends. What are the wavelengths of the three lowest-pitch tones produced by this pipe? A) 4L, 2L, L B) 2L, L, L/2 C) 2L, L, 2L/3 D) 4L, 4L/3, 4L/5 Answer: C Var: 1

13) An pipe of length L that is open at both ends is resonating at its fundamental frequency. Which statement about the sound is correct? A) The wavelength is 2L and there is a displacement node at the pipe's midpoint. B) The wavelength is 2L and there is a displacement antinode at the pipe's midpoint. C) The wavelength is L and there is a displacement node at the pipe's midpoint. D) The wavelength is L and there is a displacement antinode at the pipe's midpoint. Answer: A Var: 1

14) In a resonating pipe that is open at one end and closed at the other, there A) are displacement nodes at each end. B) are displacement antinodes at each end. C) is a displacement node at the open end and a displacement antinode at the closed end. D) is a displacement node at the closed end and a displacement antinode at the open end. Answer: D Var: 1

3 Copyright © 2014 Pearson Education, Inc. 15) Consider a pipe of length L that is open at one end and closed at the other end. What are the wavelengths of the three lowest-pitch tones produced by this pipe? A) 4L, 2L, L B) 2L, L, L/2 C) 2L, L, 2 L/3 D) 4L, 4L/3, 4L/5 Answer: D Var: 1

16) A pipe of length L that is closed at one end and open at the other end is resonating at its fundamental frequency. Which statement about the sound is correct? A) The wavelength is 4L and there is a displacement node at the pipe's open end. B) The wavelength is 4L and there is a displacement antinode at the pipe's open end. C) The wavelength is L and there is a displacement node at the pipe's open end. D) The wavelength is L and there is a displacement antinode at the pipe's open end. Answer: B Var: 1

17) Two tuning forks have frequencies of 440 and 522 Hz. What is the beat frequency if both are sounding simultaneously? A) 962 Hz B) 481 Hz C) 82 Hz D) 55 Hz E) 41 Hz Answer: C Var: 1

18) Two strings both vibrate at exactly 819 Hz. The tension in one of them is then increased slightly. As a result, six beats per second are heard when both strings vibrate. What is the new frequency of the string that was tightened? A) 825 Hz B) 813 Hz C) 822 Hz D) 816 Hz Answer: A Var: 50+

19) Two pure tones are sounded together and a particular beat frequency is heard. What happens to the beat frequency if the frequency of one of the tones is increased? A) It increases. B) It decreases. C) It does not change. D) It could either increase or decrease. Answer: D Var: 1

4 Copyright © 2014 Pearson Education, Inc. 20) A music tuner uses a 554-Hz C# tuning fork to tune the frequency of a musical instrument. If the tuner hears a beat frequency of 2 Hz, what is the frequency of the instrument? A) It must be 556 Hz. B) It must be 552 Hz. C) It could be either 556 Hz or 552 Hz. D) It could be either 553 Hz or 555 Hz. E) It is neither 556 Hz or 552 Hz. Answer: C Var: 1

21) As you are moving very quickly toward a speaker emitting a pure tone, which characteristics of the sound get larger? (There may be more than one correct choice.) A) frequency B) amplitude C) wavelength D) period E) loudness Answer: A, E Var: 1

22) In many cartoon shows, a character runs off a cliff, realizes his predicament, and lets out a scream. He continues to scream as he falls. If the physical situation is portrayed correctly, from the vantage point of an observer at the top of the cliff leaning over the edge, the pitch of the scream as he falls should be A) higher than the original pitch and constant. B) higher than the original pitch and increasing as he falls. C) lower than the original pitch and constant. D) lower than the original pitch and decreasing as he falls. E) It is impossible to predict. Answer: D Var: 1

23) In many cartoon shows, a character runs off a cliff, realizes his predicament, and lets out a scream. He continues to scream as he falls. If the physical situation is portrayed correctly, from the vantage point of an observer at the foot of the cliff, the pitch of the scream as he falls should be A) higher than the original pitch and constant. B) higher than the original pitch and increasing as he falls. C) lower than the original pitch and constant. D) lower than the original pitch and decreasing as he falls. E) It is impossible to predict. Answer: B Var: 1

5 Copyright © 2014 Pearson Education, Inc. 24) A person stands between two speakers driven by the same source. Each speaker produces a tone with a frequency of 200 Hz on a day when the speed of sound is 330 m/s. The person is 1.65 m from one speaker and 4.95 m from the other. What type of interference does the person perceive? A) constructive B) destructive C) both constructive and destructive D) neither constructive nor destructive Answer: A Var: 1

25) A sonic boom occurs only as an airplane just reaches the speed of sound in air, but not after it increases its speed further. A) True B) False Answer: B Var: 1

26) As a supersonic airplane increases its speed more and more, the half-angle of the conical shock wave A) increases. B) decreases. C) is not affected. Answer: B Var: 1

12.2 Problems

1) An elephant can hear sound with a frequency of 15 Hz. What is the wavelength of this wave if the speed of sound in air is 343 m/s? Answer: 23 m Var: 1

2) You drop a stone down a well that is 9.5 m deep. How long is it before you hear the splash? The speed of sound in air is 343 m/s and air resistance is negligible. A) 1.2 s B) 1.3 s C) 1.4 s D) 1.5 s E) 1.6 s Answer: C Var: 1

6 Copyright © 2014 Pearson Education, Inc. 3) The speed of sound through the ground is about 6.0 km/s while the speed of sound in air is 343 m/s. A very powerful explosion occurs some distance away and you feel the ground vibrate 60 seconds before you hear the sound of the explosion. How far away is the explosion? A) 20 km B) 22 km C) 25 km D) 27 km E) 30 km Answer: B Var: 1

4) Two motors in a factory are running at slightly different rates. One runs at 825.0 rpm and the other at You hear the sound intensity increase and then decrease periodically due to wave interference. How long does it take between successive instances of the sound intensity increasing? A) 1.54 s B) 1.43 s C) 1.66 s D) 1.79 s Answer: A Var: 44

5) A plucked guitar string produces a sound wave of frequency 0.44 kHz on a day when the speed of sound is 340 m/s. (a) What is the wavelength of the sound wave? (b) How much time elapses between the impacts of two adjacent compressions of the sound wave on your eardrum? Answer: (a) 0.77 m (b) 2.3 ms Var: 1

6) What is the intensity level in decibels of a sound with intensity 10-3 W/m2? The threshold of human hearing is 1.0 × 10-12 W/m2. A) 30 dB B) 60 dB C) 90 dB D) 96 dB Answer: C Var: 1

7) What is the intensity of a 70-dB sound? The threshold of human hearing is 1.0 × 10-12 W/m2. A) 10-4 W/m2 B) 10-5 W/m2 C) 10-6 W/m2 D) 10-7 W/m2 Answer: B Var: 1

9) If the intensity level by 15 identical engines in a garage is 100 dB, what is the intensity level generated by each one of these engines? A) 67 dB B) 13 dB C) 44 dB D) 88 dB Answer: D Var: 1

10) The intensity at a distance of 6.0 m from a source that is radiating equally in all directions is 6.0 × 10-10 W/m2. What is the power emitted by the source? A) 2.1 × 10-8 W B) 2.7 × 10-7 W C) 2.1 × 10-6 W D) 2.7 × 10-5 W Answer: B Var: 1

11) The intensity at a distance of 6.0 m from a source that is radiating equally in all directions is 6.0 × 10-10 W/m2. What is the intensity level in dB? The threshold of human hearing is 1.0 × 10-12 W/m2. A) 18 dB B) 23 dB C) 28 dB D) 32 dB Answer: C Var: 1

12) A barking dog delivers about 1.0 mW of power, which is assumed to be uniformly distributed in all directions. What is the intensity level in decibels at a distance 5.00 m from the dog? The threshold of human hearing is 1.0 × 10-12 W/m2. A) 61 dB B) 63 dB C) 65 dB D) 68 dB Answer: C Var: 1 8 Copyright © 2014 Pearson Education, Inc. 13) The intensity level is 65 dB at a distance 5.00 m from a barking dog. What would be a reasonable estimate for the intensity level if two identical dogs very close to each other were barking? You can ignore any interference effects. A) 65 dB B) 68 dB C) 130 dB D) 136 dB Answer: B Var: 1

14) At a distance of 15.0 m from a sound source, the intensity level is 60.0 dB. What is the intensity level (in decibels) at a point 2.00 m from the source if the source radiates equally in all directions? A) 55.7 dB B) 57.5 dB C) 75.5 dB D) 77.5 dB Answer: D Var: 1

15) The sound intensity level 5.0 m from a point source is 95 dB. At what distance will it be 75 dB? A) 25 m B) 50 m C) 75 m D) 225 m Answer: B Var: 1

16) A certain siren radiates sound uniformly in all directions. At a distance of 17 m from the siren, the intensity level is 49 db. How many watts of power does this siren put out? The threshold of human hearing is 1.0 × 10-12 W/m2. Answer: 2.9 × 10-4 W Var: 50+

17) You double your distance from a sound source that is radiating equally in all directions. What happens to the intensity level of the sound? It drops by A) 2 dB. B) 3 dB. C) 6 dB. D) 8 dB. Answer: C Var: 1

9 Copyright © 2014 Pearson Education, Inc. 18) By how many decibels does the intensity level of a sound decrease when you triple your distance from a source of sound? A) 9.5 dB B) 4.8 dB C) 6.0 dB D) 12 dB E) 3.0 dB Answer: A Var: 1

19) A certain factory whistle can be heard up to a distance of 2.5 km. Assuming that the acoustic output of the whistle is uniform in all directions, how much acoustic power is emitted by the whistle? The threshold of human hearing is 1.0 × 10-12 W/m2. A) 0.079 mW B) 0.026 mW C) 0.26 mW D) 0.79 mW E) 2.6 mW Answer: A Var: 50+

20) A certain factory whistle can be heard up to a distance of 9.8 km. Assuming that the acoustic output of the whistle is uniform in all directions, at what distance from the factory is the intensity level of the whistle sound equal to 25 dB? The threshold of human hearing is 1.0 × 10-12 W/m2. A) 550 m B) 660 m C) 830 m D) 940 m E) 1100 m Answer: A Var: 50+

21) By how many decibels does the intensity level of a sound increase when you triple the intensity of a source of sound? A) 9.5 dB B) 4.8 dB C) 6.0 dB D) 3.0 dB E) 12 dB Answer: B Var: 1

10 Copyright © 2014 Pearson Education, Inc. 22) A sound of 40 decibels is A) twice as intense as a sound of 20 decibels. B) four times as intense as a sound of 20 decibels. C) 10 times as intense as a sound of 20 decibels. D) 100 times as intense as a sound of 20 decibels. E) 1000 times as intense as a sound of 20 decibels. Answer: D Var: 1

23) A long-term exposure to the sound of a riveting machine can cause your threshold of hearing to shift from 0 dB to 30 dB. What is the sound intensity of a 30-dB sound? The normal lowest detectable intensity is 1.0 × 10-12 W/m2. Answer: 1.0 × 10-9 W/m2 Var: 1

24) A certain glass window reduces the intensity level of the sound from 72 dB to 47 dB. By what factor is the acoustic power reduced by this glass window? A) 3.2 × 10-3 B) 2.2 × 10-2 C) 5.6 × 10-2 D) 1.0 × 10-1 E) 1.5 × 10-1 Answer: A Var: 50+

25) Two people are talking at a distance of 3.0 m from where you are, and you measure the sound intensity as 1.1 × 10-7 W/m2. Another student is 4.0 m away from the talkers. Calculate a reasonable estimate for the sound intensity that the other student measures. A) 6.2 × 10-8 W/m2 B) 1.5 × 10-7 W/m2 C) 8.3 × 10-8 W/m2 D) 7.8 × 10-7 W/m2 E) 2.5 × 10-8 W/m2 Answer: A Var: 1

11 Copyright © 2014 Pearson Education, Inc. 26) A crying baby emits sound with an intensity of 8.0 × 10-8 W/m2. Calculate a reasonable estimate for the intensity level from a set of quintuplets (five babies), all crying simultaneously at the same place? The lowest detectable intensity is 1.0 × 10-12 W/m2. A) 79 dB B) 69 dB C) 56 dB D) 49 dB E) 36 dB Answer: C Var: 1

27) If the intensity level of one trombone is 70 dB, calculate a reasonable estimate for the intensity level of 76 trombones all playing simultaneously in the same place? A) 146 dB B) 89 dB C) 70 dB D) 76 dB E) 82 dB Answer: B Var: 1

28) An organ pipe that is 1.75 m long and open at both ends produces sound of frequency 303 Hz when resonating in its second overtone. What is the speed of sound in the room? Answer: 354 m/s Var: 1

29) An organ pipe closed at one end and open at the other end has two successive harmonics with frequencies of 2170 Hz and 2790 Hz. What is the fundamental frequency of the pipe? Answer: 310 Hz Var: 1

30) A pipe that is 0.92 m long and open at both ends vibrates in the second overtone with a frequency of What is the speed of sound in the air in this pipe? A) 358 m/s B) 349 m/s C) 353 m/s D) 344 m/s E) 363 m/s Answer: A Var: 50+

31) A standing wave of the third overtone is induced in a 1.2-m pipe that is open at one end and closed at the other end. The speed of sound in the pipe is 340 m/s. (a) How many antinodes are there in the standing wave pattern? (b) What is the frequency of the sound produced by the pipe in this situation? Answer: (a) 4 (b) 500 Hz Var: 1 12 Copyright © 2014 Pearson Education, Inc. 32) An organ pipe open at both ends has a length of 0.80 m. If the velocity of sound in air is what is the frequency of the second harmonic of this pipe? A) 213 Hz B) 425 Hz C) 638 Hz D) 850 Hz Answer: B Var: 2

33) What is the length of the shortest pipe closed on one end and open at the other end that will have a fundamental frequency of 0.060 kHz on a day when the speed of sound is 340 m/s? A) 1.24 m B) 1.42 m C) 2.14 m D) 4.12 m Answer: B Var: 1

34) Consider two pipes of the same length: one pipe is open at both ends and the other pipe is closed on one end but open at the other end. If the fundamental frequency of the totally open pipe is 300 Hz, what is the fundamental frequency of the other pipe? A) 150 Hz B) 300 Hz C) 450 Hz D) 600 Hz Answer: A Var: 1

35) One of the harmonics of a column of air in a tube that is open at one end and closed at the other has a frequency of 448 Hz, and the next higher harmonic has a frequency of 576 Hz. What is the fundamental frequency of the air column in this tube? A) 32 Hz B) 64 Hz C) 88 Hz D) 128 Hz E) 256 Hz Answer: B Var: 1

13 Copyright © 2014 Pearson Education, Inc. 36) One of the harmonics of a column of air in a tube that is open at both ends has a frequency of 448 Hz, and the next higher harmonic has a frequency of 576 Hz. What is the fundamental frequency of the air column in this tube? A) 32 Hz B) 64 Hz C) 88 Hz D) 128 Hz E) 256 Hz Answer: D Var: 1

37) One of the harmonics of a column of air in a tube that is open at one end and closed at the other has a frequency of 448 Hz, and the next higher harmonic has a frequency of 576 Hz. How long is the tube? The speed of sound in air is 343 m/s. A) 1.34 m B) 0.670 m C) 0.335 m D) 1.00 m E) 2.68 m Answer: A Var: 1

38) A 2.0-g string that is 0.67 m long is under tension. The string vibrates at 700 Hz tone in its third harmonic, and this vibration causes a sound wave. What is the wavelength of the sound? The speed of sound in air is 344 m/s. A) 0.49 B) 0.55 C) 0.61 D) 0.67 E) 0.45 Answer: A Var: 50+

39) A string that is 0.15 m long and fixed at both ends is vibrating in its n = 5 harmonic. The sound from this string excites a pipe that is long and open at both ends into its second overtone resonance. What is the distance between a node and an adjacent antinode, in the string? The speed of sound in air is 345 m/s. A) 15 mm B) 7.5 mm C) 23 mm D) 30 mm E) 150 mm Answer: A Var: 50+

14 Copyright © 2014 Pearson Education, Inc. 40) A string that is 0.26 m long is vibrating in its n = 6 harmonic. The sound from this string excites a pipe that is long and open at both ends into its second overtone resonance. What is the common resonant frequency of the string and the pipe? The speed of sound in air is 345 m/s. A) 590 Hz B) 390 Hz C) 490 Hz D) 690 Hz E) 760 Hz Answer: A Var: 50+

41) A 0.13-m string, fixed at both ends and vibrating in its n = 4 harmonic, excites a pipe that is long and open at both ends, into its second overtone resonance. What is the speed of transverse waves on the string? The speed of sound in air is 345 m/s. A) 38 m/s B) 36 m/s C) 34 m/s D) 32 m/s E) 30 m/s Answer: A Var: 50+

42) A violin with string length 32 cm and string density resonates in its fundamental with the first overtone of a 2.0-m organ pipe with one end closed and one end open. What is the tension in the string if the speed of sound in air is 344 m/s? A) 1000 N B) 110 N C) 450 N D) 4100 N E) 56 N Answer: A Var: 50+

43) Two police cars have identical sirens that produce sound of 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 measures 9.0 beats per second. Find the speed of the approaching police car. The speed of sound is 340 m/s. Answer: 5.3 m/s Var: 50+

15 Copyright © 2014 Pearson Education, Inc. 44) The wavelengths of the sounds produced by two horns are 6.0 m and 7.0 m, respectively. What beat frequency is heard when the horns are sounded on a day when the speed of sound is 340 m/s? A) 5 Hz B) 6 Hz C) 7 Hz D) 8 Hz Answer: D Var: 1

45) Two taut strings of identical mass per unit length are stretched with the same tension with their ends fixed, but one string is 0.330 cm longer than the other. Waves on these strings propagate at 34.0 m/s. The fundamental frequency of the shorter string is 258 Hz. What is the beat frequency when each string is vibrating at its fundamental frequency? A) 12.3 Hz B) 9.00 Hz C) 12.0 Hz D) 12.7 Hz E) 11.3 Hz Answer: A Var: 5

46) Two taut strings of identical mass and length are stretched with their ends fixed, but the tension in one string is 1.10 times greater than in the other. Waves on the string with the lower tension propagate at 35.2 m/s. The fundamental frequency of that string is 258 Hz. What is the beat frequency when each string is vibrating at its fundamental frequency? A) 11.0 Hz B) 9.00 Hz C) 13.7 Hz D) 12.6 Hz E) 17.1 Hz Answer: D Var: 5

47) A policeman in a stationary car measures the speed of approaching cars by means of an ultrasonic device that emits a sound with a frequency of 39.6 kHz. A car is approaching him at a speed of 35.0 m/s. The wave is reflected by the car and interferes with the emitted sound producing beats. What is the frequency of the beats when the speed of sound in air is 343 m/s? A) 5000 Hz B) 4500 Hz C) 8490 Hz D) 9000 Hz E) 4250 Hz Answer: D Var: 5

16 Copyright © 2014 Pearson Education, Inc. 48) As shown in the figure, a man is traveling on a bicycle along a straight road that runs parallel to and right next to some railroad tracks. While moving at 10 m/s, he hears the whistle of a train that is behind him, as shown in the figure. The frequency emitted by the train's whistle is but the frequency the man hears is The speed of sound is 340 m/s. (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?

Answer: a) 797 Hz b) 9.8 m/s, away from the bicycle Var: 50+

49) A factory siren indicating the end of a shift has a frequency of 80 Hz where the speed of sound in air is 343 m/s. What frequency is perceived by the occupant of a car that is traveling at 30 m/s (a) towards the factory and (b) away from the factory? Answer: (a) 87 Hz (b) 73 Hz Var: 1

50) A car approaches you at a constant speed, sounding its horn, and you hear a frequency of 76 Hz. After the car goes by, you hear a frequency of 65 Hz. What is the frequency of the sound emitted by the horn? The speed of sound in the air is 343 m/s. A) 68 Hz B) 69 Hz C) 70 Hz D) 71 Hz E) 72 Hz Answer: C Var: 1

51) As you stand by the side of the road, a car approaches you at a constant speed, sounding its horn, and you hear a frequency of 76 Hz. After the car goes by, you hear a frequency of 65 Hz. What is the speed of the car? The speed of sound in the air is 343 m/s. A) 26 m/s B) 27 m/s C) 28 m/s D) 29 m/s E) 30 m/s Answer: B Var: 1

17 Copyright © 2014 Pearson Education, Inc. 52) You are driving along a highway at 35.0 m/s when you hear the siren of a police car approaching you from behind at constant speed and you perceive the frequency as . You are relieved that he is in pursuit of a different driver when he continues past you, but now you perceive the frequency as What is the speed of the police car? The speed of sound in air is A) 38.4 m/s B) 30 m/s C) 39.2 m/s D) 40.1 m/s E) 41.7 m/s Answer: D Var: 5

53) You are driving along a highway at 35.0 m/s when you hear the siren of a police car approaching you from behind at constant speed and you perceive the frequency as 1310 Hz. You are relieved that he is in pursuit of a different driver when he continues past you, but now you perceive the frequency as 1240 Hz. What is the frequency of the siren in the police car? The speed of sound in air is 343 m/s. A) 1300 Hz B) 1320 Hz C) 1270 Hz D) 1360 Hz E) 1370 Hz Answer: C Var: 5

54) You are driving along a highway at 25 m/s when you hear the siren of an emergency vehicle traveling at constant speed in the opposite direction on the other side of the highway. When the vehicle is approaching you, you hear the frequency of the siren as 2380 Hz, but when it is past you the frequency becomes 1680 Hz. What is the speed of the vehicle? The speed of sound in air is 343 m/s. A) 35 m/s B) 32 m/s C) 30 m/s D) 41 m/s E) 50 m/s Answer: A Var: 5

18 Copyright © 2014 Pearson Education, Inc. 55) You are driving along a highway at 25.0 m/s when you hear the siren of an emergency vehicle traveling at constant speed in the opposite direction on the other side of the highway. When the vehicle is approaching you, you hear the frequency of the siren as 2380 Hz, but when it is past you the frequency becomes 1680 Hz. What is the frequency of the siren? The speed of sound in air is 343 m/s. A) 1850 Hz B) 2000 Hz C) 2050 Hz D) 2010 Hz E) 1980 Hz Answer: B Var: 5

56) A whistle produces sound of frequency of 1.00 kHz. If a listener moves with a speed of 30 m/s away from the whistle, what frequency does this person hear if the sound speed is 340 m/s? A) 912 Hz B) 919 Hz C) 1000 Hz D) 1090 Hz Answer: A Var: 1

57) A police car has an 800-Hz siren. It is traveling at 35.0 m/s on a day when the speed of sound through air is 340 m/s. The car approaches and passes an observer who is standing along the roadside. What change of frequency does the observer hear? A) 0 Hz B) 82 HZ C) 166 Hz D) 249 Hz Answer: C Var: 1

58) What is the frequency does a stationary observer hear when a train approaches her with a speed of 30 m/s. The frequency of the train horn is 0.600 kHz and the speed of sound is 340 m/s. A) 551 Hz B) 600 Hz C) 653 Hz D) 658 Hz Answer: D Var: 1

19 Copyright © 2014 Pearson Education, Inc. 59) You are moving at 120 km/h toward a stationary train. The train blows its 0.400-kHz whistle. Take the speed of sound to be 340 m/s. What frequency do you hear? A) 444 Hz B) 439 Hz C) 364 Hz D) 361 Hz Answer: B Var: 1

60) A train is traveling away from you at 120 km/h. It blows its whistle, and you hear a tone of 0.400 kHz. Take the speed of sound to be 340 m/s. What frequency does the whistle actually produce? A) 444 Hz B) 439 Hz C) 364 Hz D) 361 Hz Answer: B Var: 1

61) Sonar is used to determine the speed of an object. A 40.0-kHz signal is sent out, and a 42.0- kHz signal is returned. If the speed of sound is 345 m/s, how fast is the object moving? A) 6.9 m/s B) 8.4 m/s C) 331 m/s D) 347 m/s Answer: B Var: 1

62) A bat emits a sound at a frequency of 39.0 kHz as it approaches a wall. The bat detects beats with a frequency of 827 Hz between the sound it emits and the echo bouncing from the wall. What is the speed of the bat if the speed of sound in air is 343 m/s? A) 2.7 m/s B) 3.0 m/s C) 3.6 m/s D) 5.4 m/s E) 9.0 m/s Answer: C Var: 5

20 Copyright © 2014 Pearson Education, Inc. 63) Two in-phase loudspeakers are some distance apart. They emit sound with a frequency of 536 Hz. A microphone is moved between the speakers along the line joining the two speakers with a constant speed of 1.60 m/s. What beat frequency is observed? The speed of sound in air is 343 m/s. A) 5.00 Hz B) 6.00 Hz C) 7.00 Hz D) 8.00 Hz E) 9.00 Hz Answer: A Var: 1

64) A siren emitting sound of frequency 1000 Hz approaches a stationary observer at one-half the speed of sound. The observer hears a frequency of A) 1000 Hz B) 2000 Hz. C) 500 Hz. D) 1500 Hz. E) none of the above. Answer: B Var: 1

65) The sound from the whistle of a truck moving at 17.0 m/s toward a cliff reflects from the cliff and is heard by the driver of the truck. When it is parked at the side of the road, the whistle from the truck produces sound of frequency 2.267 kHz. As observed by the driver of the truck, what is the change in frequency the sound from the whistle due to the reflection? The speed of sound is 343 m/s. A) 236 Hz B) 228 Hz C) 207 Hz D) 118 Hz E) 472 Hz Answer: A Var: 1

66) Two in-phase loudspeakers are 3.0 m apart. They emit sound with a frequency of 490 Hz. A microphone is placed half-way between the speakers and then moved along the line joining the two speakers until the first point of constructive interference is found. At what distance from that midpoint is that first point? The speed of sound in air is 343 m/s. A) 0.18 m B) 0.35 m C) 0.50 m D) 0.70 m E) There is no point in that line where constructive interference occurs. Answer: B Var: 1

21 Copyright © 2014 Pearson Education, Inc. 67) Two in-phase loudspeakers are placed along a wall and are separated by a distance of 4.00 m. They emit sound with a frequency of 514 Hz. A person is standing away from the wall, in front of one of the loudspeakers. What is the closest nonzero distance from the wall the person can stand and hear constructive interference? The speed of sound in air is 343 m/s. A) 0.34 m B) 0.73 m C) 1.2 m D) 1.6 m Answer: B Var: 1

68) Two in-phase loudspeakers are placed along a wall and are separated by a distance of 4.00 m. They emit sound with a frequency of 514 Hz. A person is standing away from the wall, in front of one of the loudspeakers. What is the closest distance from the wall the person can stand and hear destructive interference? The speed of sound in air is 343 m/s. A) 0.34 m B) 0.37 m C) 0.73 m D) 1.2 m E) 1.6 m Answer: A Var: 1

69) Two in-phase loudspeakers that emit sound with the same frequency are placed along a wall and are separated by a distance of 5.00 m. A person is standing 12.0 m away from the wall, equidistant from the loudspeakers. When the person moves 1.00 m parallel to the wall, she experiences destructive interference for the first time. What is the frequency of the sound? The speed of sound in air is 343 m/s. A) 211 Hz B) 256 Hz C) 422 Hz D) 512 Hz E) 674 Hz Answer: C Var: 1

22 Copyright © 2014 Pearson Education, Inc. 70) Two in-phase loudspeakers that emit sound with the same frequency are placed along a wall and are separated by a distance of 8.00 m. A person is standing 12.0 m away from the wall, equidistant from the loudspeakers. When the person moves 3.00 m parallel to the wall, she experiences destructive interference for the second time. What is the frequency of the sound? The speed of sound in air is 343 m/s. A) 278 Hz B) 422 Hz C) 452 Hz D) 562 Hz E) 694 Hz Answer: A Var: 1

71) Two loudspeakers placed 6.00 m apart are driven in phase by an audio oscillator having a frequency range from 1908 Hz to 2471 Hz. A point P is located 4.70 m from one loudspeaker and 3.60 m from the other speaker. At what frequency of the oscillator does the sound reaching point P interfere constructively? The speed of sound is 344 m/s. A) 2190 Hz B) 2420 Hz C) 2110 Hz D) 2340 Hz E) 2270 Hz Answer: A Var: 1

72) Two loudspeakers placed 6.00 m apart are driven in phase by an audio oscillator having a frequency range from 1595 Hz to 2158 Hz. A point P is located 4.70 m from one loudspeaker and 3.60 m from the other speaker. The speed of sound in the room is 344 m/s. At what frequency (or frequencies) of the oscillator does the sound reaching point P interfere destructively? (There could be more than one correct choice.) A) 2030 Hz B) 2130 Hz C) 2100 Hz D) 1720 Hz E) 1630 Hz Answer: A, D Var: 1

23 Copyright © 2014 Pearson Education, Inc. 73) Two stereo speakers mounted 4.52 m apart on a wall emit identical sound waves. You are standing at the opposite wall of the room at a point directly between the two speakers. You walk 2.11 m parallel to the wall, to a location where you first notice that the sound intensity is essentially zero. If the wall along which you are walking is from the wall with the speakers, what is the wavelength of the sound waves? The walls are cushioned to absorb sound reflections. A) 1.71 m B) 2.05 m C) 2.57 m D) 2.91 m Answer: A Var: 50+

74) Two speakers are placed side by side and driven by the same frequency of 0.50 kHz. If the distance from a person to one speaker is 5.0 m and the person detects little or no sound, which of the following is a possible the distance from the person to the other speaker? The sound speed in the room is 340 m/s. A) 7.7 m B) 8.1 m C) 8.4 m D) 9.1 m Answer: B Var: 1

75) The half-angle of the conical shock wave produced by a supersonic aircraft is 60°. What is the ratio of the speed of the aircraft to the speed of sound? A) 0.87 B) 1.2 C) 1.7 D) 2.0 Answer: B Var: 1

76) A jet flies at 1.4 times the speed of sound. What is the half-angle of the conical shock wave formed? A) 30° B) 36° C) 44° D) 46° Answer: D Var: 1