Sound 14.1 Conceptual Questions ____ 1) When a guitar is tuned to adjust it pitch, what is it that is changed? A) The wavelength of the fundamental. B) The frequency of the fundamental. C) The amplitude of the fundamental. ____ 2) 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. ____ 3) 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 ____ 4) 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 A travels faster than sound B through air. E) The amplitude of A is larger than the amplitude of B. ____ 5) 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 ____ 6) 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. ____ 7) 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. ____ 8) 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. ____ 9) 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. ____ 10) 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 ____ 11) 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 ____ 12) 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. ____ 13) 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 ____ 14) 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. ____ 15) 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. ____ 16) 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 ____ 17) 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. ____ 18) 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 ____ 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. ____ 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. ____ 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 ____ 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. ____ 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. 14.2 Problems 24) 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? ____ 25) 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 ____ 26) 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) C) D) E) 22 km 25 km 27 km 30 km 27) 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? ____ 28) 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 ____ 29) 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 ____ 30) 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 31) 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? ____ 32) A pipe that is 0.92 m long and open at both ends vibrates in the second overtone with a frequency of A) B) C) D) E) What is the speed of sound in the air in this pipe? 358 m/s 349 m/s 353 m/s 344 m/s 363 m/s 33) 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? ____ 34) 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 ____ 35) 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 ____ 36) 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 ____ 37) 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 38) 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? ____ 39) 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 ____ 40) 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) B) C) D) 0 Hz 82 HZ 166 Hz 249 Hz ____ 41) 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 ____ 42) 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 ____ 43) 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 ____ 44) 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 ____ 45) 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