Principle and Applications (Sound) Answer Key Part 3

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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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