Mastering Physics Solutions Chapter 14 Waves and Sounds
Chapter 14 Waves and Sounds Q.1CQ
A long nail has been driven halfway into the side of a barn. How should you hit the nail with a hamm er to generate a longitudinal wave? How should you hit it to generate a transverse wave?
Solution:
For generating a longitudinal wave, jwe hit the nail on the head in the direction parallel to its length[ In order to generate transverse waves, the nail is hit ¡n a direction perpendicular to its Iength
Chapter 14 Waves and Sounds Q.1P
A wave travels along a stretched horizontal rope. The vertical distance from crest to trough for this wave is 13 cm and the horizontal distance from crest to trough is 28 cm. What are (a) the wavelength and (b) the amplitude of this wave?
Solution:
Chapter 14 Waves and Sounds Q.2CQ
Wriat type of wave ¡s exhibited by “amber waves of grain”?
Solution:
IWaves passing through a grain field are longitudinal waves I The motion of each grain stalk is in the same direction as the motion of the wave itself
Chapter 14 Waves and Sounds Q.2P
A surfer floating beyond the breakers notes 14 waves per minute passing her position. If the wavelength of these waves is 34 m, what is their speed?
Solution:
Chapter 14 Waves and Sounds Q.3CQ
At a ball game. a “wave” circulating through the stands can be an exciting event What type of wave {longitudinal or transverse) are we talking about? Is it possible to change the type of wave? Explain how people might move their bodies to accomplish this.
Solution:
At a ball game. the stadium waves circulating through stands in rows are hransverse waves I In order to change the type of wave, the people in stands should move toward their left or right to create longitudinal waves
Chapter 14 Waves and Sounds Q.3P
The speed of surface waves in water decreases as the water becomes shallower. Suppose waves travel across the surface of a lake with a speed of 2.0 m/s and a wavelength of 1.5 m. When these waves move into a shallower part of the lake, their speed decreases to 1.6 m/s, though their frequency remains the same. Find the wavelength of the waves in the shallower water.
Solution:
Chapter 14 Waves and Sounds Q.4CQ
In a classic TV commercial, a group of cats feed from bowls of cat food that are lined up side by sida Initially there is one cat for each bowl When an additional cat is added to the scene, it runsto a bowl at the end of the line and begins to eat The cat that was there originally moves to the next bowl, displacing that cat. which moves to the next bowl, and so on down the lina What type of wave have the cats created’ Explain
Solution:
IThis wave is longitudinall since each cat moves in the same direction as the wave
Chapter 14 Waves and Sounds Q.4P
Tsunami A tsunami traveling across deep water can have a speed of 750 Km/h and a wavelength of 310 km. What is the frequency of such a wave?
Solution:
Chapter 14 Waves and Sounds Q.5CQ
Describe how the Sound of a symphony played by an orchestra would be altered if the speed of Sound depended on the frequency of sound
Solution:
lithe speed of Sound depended on frequency, the sound in the first row, where the travel time is very small, would not be affected significantly. Farther back from the stage. however, sounds with different frequencies would arrive at different times The bass would be out of synchronization with the treble
Chapter 14 Waves and Sounds Q.5P
4.5-Hzwave with an amplitude of 12 cm and a wavelength of 27 cm travels along a stretched horizontal string. (a) How far does a given peak on the wave travel in a time interval of 0.50 s? (b) How far does a knot on the string travel in the same time interval? (c) How would your answers to parts (a) and (b) change if the amplitude of the wave were halved? Explain.
Solution:
c) The distance traveled by the peak wave is independent of the amplitude. Thus, there will be no effect for part (a), and so it remains unchanged. For part (b), the distance traveled by the knot is directly proportional to the amplitude. When the amplitude is halved, then the distance is also halved.
Chapter 14 Waves and Sounds Q.6CQ
A “radar gun” is often used to measure the speed of a major league pitch by reflecting a beam of radio waves off a moving ball. Describe how the Doppler effect can give the speed of the ball from a measurement of the frequency of the reflected beam.
Solution:
Concept:
The observed frequency of a sound wave when the source is moving with a speed u and the observer is at rest is given as follows.
Chapter 14 Waves and Sounds Q.6P
Solution:
Chapter 14 Waves and Sounds Q.7CQ
When you drive a nail into a piece of wood, you hear a tone with each blow of the hammer. In fact, the tone increases in pitch as the nail is driven farther into the wood Explain
Solution:
When the nail drives into the piece of wood, the portion that is not in the wood decreases. Therefore, the portion that is vibrating decreases This vibrating portion of the nail is similar to the vibrating column of a pipe organ Therefore, when the length of the vibrating nail decreases, the wavelength associated with the vibrating nail also decreases. Therefore, the frequency of the nail increases
Chapter 14 Waves and Sounds Q.7P
Solution:
Chapter 14 Waves and Sounds Q.8CQ
Explain the function of the sliding part of a trombone
Solution:
The sliding part of a trombone varies the length of the vibrating air column that produces the trombonWs sound IBY adjusting this length. the player controls the resonant frequency of the instrumen This, in turn, varies the frequency of the Sound produced by the trombone
Chapter 14 Waves and Sounds Q.8P
Consider a wave on a string with constant tension. If the frequency of the wave is doubled, by what multiplicative factor does (a) the speed and (b) the wavelength change?
Solution:
Chapter 14 Waves and Sounds Q.9CQ
When you tune a violin string, what causes its frequency to change?
Solution:
Chapter 14 Waves and Sounds Q.9P
Suppose you would like to double the speed of a wave on a string. By what multiplicative factor must you increase the tension?
Solution:
Chapter 14 Waves and Sounds Q.10CQ
On a guitar. some strings are single wires, others are wrapped with another wire to increase the mass per Iength Which type of string would you expect to be used for a low-frequency note? Explain
Solution:
The thicker string is used to produce the low frequency notes. This is because the frequency of the fundamental depends directly on the speed of the waves on the string Therefore, for a given tension, a string with a greater mass per length has a smaller wave speed and a lower frequency
Chapter 14 Waves and Sounds Q.10P
Two strings are made of the same material and have equal tensions. String 1 is thick; string 2 is thin, (a) Is the speed of waves on string 1 greater than, less than, or equal to the speed of waves on string 2? (b) Choose the besi explanation from among the following:
I. Since the strings are made of the same material, the wave speeds will also be the same.
II. A thick string implies a large mass per length and a slow wave speed.
III. A thick string has a greater force constant, and therefore a greater wave speed.
Solution:
Chapter 14 Waves and Sounds Q.11CQ
As a string oscillates in its fundamental mode, there are times when it is completely flat. Is the energy of oscillation zero at these times? Explain.
Solution:
Chapter 14 Waves and Sounds Q.11P
Two strings are made of the same material and have waves of equal speed. String 1 is thick; string 2 is thin, (a) Is the tension in string 1 greater than, less than, or equal to the tension in string 2? (b) Choose the best explanation from among the following:
I. String 1 must have a greater tension to compensate for its greater mass per length.
II. String 2 will have a greater tension because it is thinner than string 1.
III. Equal wave speeds implies equal tensions.
Solution:
Chapter 14 Waves and Sounds Q.12CQ
On a rainy day, while driving your car, you notice that your windshield wipers are moving in synchrony with the wiper blades of the car in front of you. After several cycles, however your wipers and the wipers of the other car are moving opposite to one another. A short time later the wipers are synchronous again. What wave phenomena do the wipers illustrate? Explain.
Solution:
You have just observed a series of beats between your wipers and the wipers of the other car.
Chapter 14 Waves and Sounds Q.12
Solution:
Chapter 14 Waves and Sounds Q.13CQ
To play a C major chord on the piano, you hit the C, E, and G keys simultaneously. When you do so, you hear no beats. Why?
Solution:
You hear no beats because the difference in frequency between these notes is too great to produce detectable beats.
Chapter 14 Waves and Sounds Q.13P
Waves on a particular string travel with a speed of 16 m/s. By what factor should the tension in this string be changed to produce waves with a speed of 32 m/s?
Solution:
The speed of the waves on a string are given by
Thus, the new tension in the string will need to be increased by a factor of 4.
Chapter 14 Waves and Sounds Q.14P
Solution:
Chapter 14 Waves and Sounds Q.15P
Solution:
Chapter 14 Waves and Sounds Q.16P
A 5.2-m wire with a mass of 87 g is attached to the mast of a sailboat. If the wire is given a “thunk” at one end, it takes 0.094 s for the resulting wave to reach the other end. (a) What is the tension in the wire? (b) Wou!d the tension found in part (a) be larger or smaller if the mass of the wire is greater than 87 g? (c) Calculate the tension for a 97-g wire.
Solution:
Chapter 14 Waves and Sounds Q.17P
Two steel guitar strings have the same length. String A has a diameter of 0.50 mm and is under 410.0 N of tension. String B has a diameter of 1.0 mm and is undera tension of 820.0 N. Find the ratio of the wave speeds, vA/vB, in these two strings.
Solution:
Chapter 14 Waves and Sounds Q.18P
Use dimensional analysis to show how the speed v of a wave on a string of circular cross section depends on the tension in the string, T, the radius of the string, R, and its mass per volume, p.
Solution:
Chapter 14 Waves and Sounds Q.19P
Write an expression for a harmonic wave with an amplitude of 0.16 m, a wavelength of 2.1 m, and a period of 1.8 s. The wave is transverse, travels to the right, and has a displacement of 0.16 m at t = 0 and x = 0.
Solution:
Chapter 14 Waves and Sounds Q.20P
Write an expression for a transverse harmonic wave that has a wavelength of 2.6 m and propagates to the right with a speed of 14.3 m/s. The amplitude of the wave is 0.11 m, and its displacement at t = 0 and x = 0 is 0.11 m.
Solution:
Chapter 14 Waves and Sounds Q.21P
The vertical displacement of a wave on a string is described by the equation y(x, t) = A sin(Bx − Ct), in which A, B, and C are positive constants, (a) Does this wave propagate in the positive or negative x direction? (b) What is the wavelength of this wave? (c) What is the frequency of this wave? (d) What is the smallest positive value of x where the displacement of this wave is zero at t = 0?
Solution:
Chapter 14 Waves and Sounds Q.22P
The vertical displacement of a wave on a string is described by the equation y(x, t) = A sin(Bx + Ct),in which A, B, and C are positive constants, (a) Does this wave propagate in the positive or negative x direction? (b) What is the physical meaning oi the constant A? (c) What is the speed of this wave? (d) What is the smallest positive time t for which the wave has zero displacement at the point x = 0?
Solution:
Chapter 14 Waves and Sounds Q.23P
Solution:
Chapter 14 Waves and Sounds Q.24P
Consider the wave function given in the previous problem. Sketch this wave from x = 0 to x = 10 cm for the following times: (a) t = 0; (b) t = 3.0s; (c) t = 6.0 s. (d) What is the least amount of time required for a given point on this wave to move from y = 0 to y = 15 cm? Verify your answer by referring to the sketches for parts (a), (b), and (c).
Solution:
Chapter 14 Waves and Sounds Q.25P
Four waves are described by the following equations, in which all distances are measured in centimeters and all times are measuredin seconds:
yA = 1.0 cos(3x − 4t)
yB = 10 cos(5x + 4t)
yC = 20 cos(−10x + 60t)
yD = 20 cos(−4x − 20t)
(a) Which of these waves travel in the +x direction? (b) Which of these waves travel in the − x direction? (c) Which wave has the highestfrequency? (d) Which wave has the greatest wavelength? (e) Which wave has the greatest speed?
Solution:
Chapter 14 Waves and Sounds Q.26P
At Zion National Park a loud shout produces an echo 1.80 s later from a colorful sandstone cliff. How far away is the cliff?
Solution:
Chapter 14 Waves and Sounds Q.27P
Dolphin Ultrasound Dolphins of the open ocean are classified as Type II Odontocetes (toothed whales). These animals use ultrasonic “clicks” with a frequency of about 55 kHz to navigate and find prey, (a) Suppose adolphin sends out a series of clicks that are reflected back from the bottom of the ocean 75 m below. How much time elapses before the dolphin hears the echoes of the clicks? (The speed of sound in seawater is approximately 1530 m/s.) (b) What is the wavelength of 55-kHz sound in the ocean?
Solution:
Chapter 14 Waves and Sounds Q.28P
The lowest note on a piano is A, four octaves below the A given in Table 14-3. The highest note on a piano is C, four octaves above middle C. Find the frequencies and wavelengths (in air) of these notes.
Solution:
Chapter 14 Waves and Sounds Q.29P
A sound wave in air has a frequency of 425 Hz. (a) What is its wavelength? (b) If the frequency of the sound is increased, does its wavelength increase, decrease, or stay the same? Explain, (c) Calculate the wavelength for a sound wave with a frequency of 475 Hz.
Solution:
Chapter 14 Waves and Sounds Q.30P
When you drop a rock into a well, you hear the splash 1.5 seconds later, (a) How deep is the well? (b) If the depth of the well were doubled, would the time required to hear the splash be greater than, less than, or equal to 3.0 seconds? Explain.
Solution:
Chapter 14 Waves and Sounds Q.31P
A rock is thrown downward into a well that is 8.85 m deep. If the splash is heard 1.20 seconds iater, what was the initial speed of the rock?
Solution:
Chapter 14 Waves and Sounds Q.32P
If the distance to a point source of sound is doubled, by what multiplicative factor does the intensity change?
Solution:
Chapter 14 Waves and Sounds Q.33P
The intensity level of sound in a truck is 92 dB. What is the intensity of Litis sound?
Solution:
Chapter 14 Waves and Sounds Q.34P
The distance to a point source is decreased by a factor of three, (a) By what multiplicative factor does the intensity increase? (b) By what additive amount does the intensity level increase?
Solution:
Chapter 14 Waves and Sounds Q.35P
Sound 1 has an intensity of 38.0 W/m2. Sound 2 has an intensity level that is 2.5 dB greater than the intensity level of sound 1, What is the intensity of sound 2?
Solution:
Chapter 14 Waves and Sounds Q.36P
A bird-watcher is hoping to add the white-throated sparrow to her “life list” of species. How far could she be from the bird described in Example 14-3 and still be able to hear it? Assume no reflections or absorption of the sparrow’s sound.
Solution:
Chapter 14 Waves and Sounds Q.37P
Residents of Hawaii are warned of the approach of a tsunami by sirens mounted on the tops of towers. Suppose a siren produces a sound that has an intensity level of 120 dB at a distance of 2.0 m. Treating the siren as a point source of sound, and ignoring reflections and absorption, find the intensity level heard by an observer ata distance of (a) 12 m and (b) 21 m from the siren, (c) How far away can the siren be heard?
Solution:
Chapter 14 Waves and Sounds Q.38P
In a pig-calling contest, a caller produces a sound with an intensity level of 110 dB. How many such callers would be required to reach the pain level of 120 dB?
Solution:
Chapter 14 Waves and Sounds Q.39P
Twenty violins playing simultaneously with the same intensity combine to give an intensity level of 82.5 dB. (a) What is the intensity level of each violin? (b) If the number of violins is increased to 40, will the combined intensity level be more than, less than, or equal to 165 dB? Explain.
Solution:
Chapter 14 Waves and Sounds Q.40P
The Human EardrumThe radius of a typical human eardrum is about 4.0 mm. Find the energy per second received by aneardrumwhen it listens to sound that is (a) at the threshold of hearing and (b) at the threshold of pain.
Solution:
Chapter 14 Waves and Sounds Q.41P
A point source of soundthat emits uniformly in all directions is located in the middle of a large, open field. The intensity at Brittany’s location directly north of the source is twice that at Phillip’s position due east of the source. What is the distance between Brittany and Phillip if Brittany is 12.5 m from the source?
Solution:
Chapter 14 Waves and Sounds Q.42P
A horn produces sound with frequency f0. Let the frequency you hear when you are at rest and the horn moves toward you with a speed u be f1, let the frequency you hear when the horn is at rest and you move toward it with a speed u be f2.(a) Is f1 greater than, less than, or equal to f2? (b) Choose the best explanation from among the following:
I. Amoving observer encounters wave crests more often than a stationary observer, leading to a higher frequency.
II. The relative speeds are the same in either case. Therefore, the frequencies will be the same as well.
III. A moving source causes the wave crests to “bunch up,” leading to a higher frequency than for a moving observer.
Solution:
Chapter 14 Waves and Sounds Q.43P
You are heading toward an island in your speedboat when you see a friend standing on shore at the base of a cliff. You sound the boat’s horn to get your friend’s attention. Let the wavelength of the sound produced by the horn be λ1, the wavelength as heard by your friend be λ2, and the wavelength of the echo as heard on the boat be λ3. Rank these wavelengths in order of increasing length. Indicate ties where appropriate.
Solution:
Chapter 14 Waves and Sounds Q.44P
A person with perfect pitch sits on a bus bench listening to the 450-Hz horn of an approaching car. If the person detects a frequency of 470 Hz, how fast is the car moving?
Solution:
Chapter 14 Waves and Sounds Q.45P
A train moving with a speed of 31.8 m/s sounds a 136-Hz horn. What frequency is heard by an observer standing near the tracks as the train approaches?
Solution:
Chapter 14 Waves and Sounds Q.46P
In the previous problem, suppose the stationary observer sounds a horn that is identical to the one on the train. What frequency is heard from this horn by a passenger in the train?
Solution:
Chapter 14 Waves and Sounds Q.47P
A bat moving with a speed of 3.25 m/s and emitting sound of 35.0 kHz approaches a moth at rest on a tree trunk, (a) What frequency is heard by the moth? (b) If the speed of the bat is increased, is the frequency heard by the moth higher or lower? (c) Calculate the frequency heard by the moth when the speed of the bat is 4.25 m/s.
Solution:
Chapter 14 Waves and Sounds Q.48P
A motorcycle and a police car are moving toward one another. The police car emits sound with a frequency of 502 Hz and has a speed of 27.0 m/s. The motorcycle has a speed of 13.0 m/s. What frequency does the motorcyclist hear?
Solution:
Chapter 14 Waves and Sounds Q.49P
In the previous problem, suppose that the motorcycle and the police car are moving in the same direction, with the motorcycle in the lead. What frequency docs the motorcyclist hear in this case?
Solution:
Chapter 14 Waves and Sounds Q.50P
Hearing the siren of an approaching fire truck, you pull over to the side of the road and stop. As the truck approaches, you hear a tone of 460 Hz; as the truckrecedes, you hear a tone of 410 Hz. How much time will it take for the truck to get from your position to the fire 5.0 km away, assuming it maintains a constant speed?
Solution:
Chapter 14 Waves and Sounds Q.51P
With what speed must you approach a source of sound to observe a 15% change in frequency?
Solution:
Chapter 14 Waves and Sounds Q.52P
P A particular jet engine produces a tone of 495 Hz. Suppose that one jet is at rest on the tarmac while a second identical jet flies overhead at 82.5% of the speed of sound. The pilot of each jet listens to the sound produced by the engine of the other jet. (a) Which pilot hears a greater Doppler shift? Explain, (b) Calculate the frequency heard by the pilot in the moving jet. (c) Calculate the frequency heard by the pilot in the stationary jet.
Solution:
Chapter 14 Waves and Sounds Q.53P
Two bicycles approach one another, each traveling with a speed of 8.50 m/s. (a) If bicyclist A beeps a 315-Hz horn, what frequency is heard by bicyclist B? (b) Which of the following would cause the greater increase in the frequency heard by bicyclist B: (i) bicyclist A speeds up by 1.50 m/s, or (ii) bicyclist B speeds up by 1.50 m/s? Explain.
Solution:
Chapter 14 Waves and Sounds Q.54P
A train on one track moves in the same direction as a second train on the adjacent track. The first train, which is ahead of the second train and moves with a speed of 36.8 m/s, blows a horn whose frequency is 124 Hz. If the frequency heard on the second train is 135 Hz, what is its speed?
Solution:
Chapter 14 Waves and Sounds Q.55P
Two cars traveling with the same speed move directly away from one another. One car sounds a horn whose frequency is 205 Hz and a person in the other car hears a frequency of 192 Hz. What is the speed of the cars?
Solution:
Chapter 14 Waves and Sounds Q.56P
The Bullet Train The Shinkansen, the Japanese “bullet” train, runs at high speed from Tokyo to Nagoya. Riding on the Shinkansen, you notice that the frequency of a crossing signal changes markedly as you pass the crossing. As you approach the crossing, the frequency you hear is/; as you recede from the crossing the frequency you hear ig 2f/3. What is the speed of the train?
Solution:
Chapter 14 Waves and Sounds Q.57P
Solution:
Chapter 14 Waves and Sounds Q.58P
Solution:
Chapter 14 Waves and Sounds Q.59P
Solution:
Chapter 14 Waves and Sounds Q.60P
Solution:
Chapter 14 Waves and Sounds Q.61P
A pair of in-phase stereo speakers is placed side by side, 0.85 m apart. You stand directly in front of one of the speakers, 1.1 m from the speaker. What is the lowest frequency that will produce constructive interference at your location?
Solution:
Chapter 14 Waves and Sounds Q.62P
Two violinists, one directly behind the other, play for a listener directly in front of them. Both violinists sound concert A (440 Hz), (a) What is the smallest separation between the violinists that will produce destructive interference for the listener? (b) Does this smallest separation increase or decrease if the violinists produce a note with a higher frequency? (c) Re-peat part (a) for violinists who produce sounds of 540 Hz.
Solution:
Chapter 14 Waves and Sounds Q.63P
Two loudspeakers are placed at either end of a gymnasium both pointing toward the center of the gym and equidistant from it. The speakers emit 266-Hz sound that is in phase. An observer at the center of the gym experiences constructive interférence. How far toward either speaker must the observer walk to first experience destructive interference?
Solution:
Chapter 14 Waves and Sounds Q.64P
(a) In the previous problem, does the required distance increase, decrease, or stay the same if the frequency of the speakers is lowered? (b) Calculate the distance to the first position of destructive interference if the frequency emitted by the speakers is lowered to 238 Hz.
Solution:
Chapter 14 Waves and Sounds Q.65P
Solution:
Chapter 14 Waves and Sounds Q.66P
Suppose, in Example, that the speakers have opposite phase. What is the lowest frequency that gives destructive in-terference in this case?
Solution:
Chapter 14 Waves and Sounds Q.67P
When you blow across the opening of a partially filled 2-L soda pop bottle you hear a tone, (a) If you take a sip of the pop and blow across the opening again, does the tone you hear have a higher frequency, a lower frequency, or the same frequency as before? (b) Choose the best explanation from among the following:
I. The same pop bottle will give the same frequency regardless of the amount of pop it contains.
II. The greater distance from the top of the bottle to the level of the pop results in a higher frequency.
III. A lower level of pop results in a longer column of air, and hence a lower frequency.
Solution:
Chapter 14 Waves and Sounds Q.68P
An organ pipe that is open at both ends is 3.5 m long. What is its fundamental frequency?
Solution:
Chapter 14 Waves and Sounds Q.69P
A string 1.5 m long with a mass of 2.6 g is stretched between two fixed points with a tension of 93 N. Find the frequency of the fundamental on this string.
Solution:
Chapter 14 Waves and Sounds Q.70P
Astring is tied down at both ends. Some of the standing waves on this string have the following frequencies: 100 Hz, 200 Hz, 250 Hz, and 300 Hz. It is also known that there are no standing waves with frequencies between 250 Hz and,300 Hz. (a) What is the fundamental frequency of this string? (b) What is the frequency of. the third harmonic?
Solution:
Chapter 14 Waves and Sounds Q.71P
Solution:
Chapter 14 Waves and Sounds Q.72P
A guitar string 66 cm long vibrates with a standing wave that has three antinodes. (a) Which harmonic is this? (b) What is the wavelength of this wave?
Solution:
Chapter 14 Waves and Sounds Q.73P
A 12.5-g clothesline is stretched with a tension of 22, 1 N between two poles 7.66 m apart. What is the frequency of (a) the fundamental and (b) the second harmonic? (c) If the tension in the clothesline is increased, do the frequencies in parts (a) and (b) increase, decrease, or stay the same? Explain.
Solution:
Chapter 14 Waves and Sounds Q.74P
(a) In the previous problem, will the frequencies increase, decrease, or stay the same if a more massive rope is used? (b) Repeat Problem for a clothesline with a mass of 15.0 g.
Solution:
Chapter 14 Waves and Sounds Q.75P
Solution:
Chapter 14 Waves and Sounds Q.76P
Solution:
Chapter 14 Waves and Sounds Q.77P
An organ pipe open at both ends has a harmonic with a frequency of 440 Hz. The next higher harmonic in the pipe has a frequency of 495 Hz. Find (a) the frequency of the fundamental and (b) the length of the pipe.
Solution:
Chapter 14 Waves and Sounds Q.78P
When guitar strings Aand B are plucked at the same time, a beat frequency of 2 Hz is heard. If string A is tightened, the beat frequency increases to 3 Hz. Which of the two strings had the lower frequency initially?
Solution:
Chapter 14 Waves and Sounds Q.79P
(a) Is the beat frequency produced when a 245-Hz tone and a 240-Hz tone are played together greater than, less than, or equal to the beat frequency produced when a 140-Hz tone and a 145-Hz tone are pîayed together? (b) Choose the best explanation from among the following:
I. The beat frequency is determined by the difference in frequencies and is independent of their actual values.
II. The higher frequ encies will produce a higher beat frequency.
III. The percentage change in frequency for 240 and 245 Hz is less than for 140 and 145 Hz, resulting in a lower beat frequency.
Solution:
Chapter 14 Waves and Sounds Q.80P
Two tuning forks have frequencies of 278 Hz and 292 Hz. What is the beat frequency if both tuning forks are sounded simultaneously?
Solution:
Chapter 14 Waves and Sounds Q.81P
Tuning a Piano To tune middle C on a piano, a tuner hits the key and at the same time sounds a 261-Hz timing fork. If the tuner hears 3 beats per second, what arc the possible frequencies of the piano key?
Solution:
Chapter 14 Waves and Sounds Q.82P
Two musicians are comparing their clarinets. The first clarinet produces a tone that is known to be 441 Hz. When the two clarinets play together they produce eight beats every 2.00 seconds. If the second clarinet produces a higher pitched tone than the first clarinet, what is the second clarinet’s frequency?
Solution:
Chapter 14 Waves and Sounds Q.83P
Two strings that are fixed at each end are identical, except that one is 0.560 cm longer than the other. Waves on these strings propagate with a speed of 34.2 m/s, and the fundamental frequency of the shorter string is 212 Hz. (a) Wha t beat frequency is produced if each string is vibrating with its fundamentalfrequency? (b) Does the beat frequency in part (a) increase or decrease if the longer string is increased in length? (c) Repeat part (a), assuming that the longer string is 0.761 cm longer than the shorter string.
Solution:
Chapter 14 Waves and Sounds Q.84P
A tuning fork with a frequency of 320.0 Hz and a tuning fork of unknown frequency produce beats with a frequency of 4.5 Hz. If the frequency of the 320.0-Hz fork is lowered slightly by placing a bit of putty on one of its tines, the new beat frequency is 7.5 Hz. (a) Which tuning fork has the lower frequency? Explain, (b) What is the final frequency of the 320.0-Hz tuning fork? (c) What is the frequency of the other tuning fork?
Solution:
Chapter 14 Waves and Sounds Q.85P
Identical cellos are being tested, One is producing a fundamental frequency of 130.9 Hz on a string that is 1.25 m long and has a mass of 109 g. On the second cello the same string is fingered to reduce the length that can vibrate. If the beat frequency produced by these two strings is 4.33 Hz, what is the vibrating length of the second string?
Solution:
Chapter 14 Waves and Sounds Q.86P
A friend in another city tells you that she has two organ pipes of different lengths, one open at both ends, the other open at one end only. In addition, she has determined that the beat frequency caused by the second-lowest frequency of each pipe is equal to the beat frequency caused by the third-lowest frequency of each pipe. Her chauenge to you is to calculate the length of the organ pipe that is open at both ends, given that the length of the other pipe is 1.00 m.
Solution:
Chapter 14 Waves and Sounds Q.87GP
A harmonic wave travels along a string, (a) At a point where the displacement of the stringis greatest, is the kinetic energy of the string a maximumor a minimum? Explain, (b) At a point where the displacement of the string is zero, is the kinetic energy of the string a maximum or a minimum? Explain.
Solution:
(A) When the displacement of the string is at a maximum. This is because it is momentarily at rest and, thus, the kinetic energy of string is minimized, or zero.
(B) When the displacement of the string is zero or at a minimum, it possesses a maximum speed, and, thus, has maximum kinetic energy at that position.
Chapter 14 Waves and Sounds Q.88GP
A harmonic wave travels along a string, (a) At a point where the displacement of the string is greatest, is the potential energy of the string a maximum or a minimum? Explain. (b) At a point where the displacement of the string is zero, is the potential energy of the string a maximum or a minimum? Explain.
Solution:
(A) When the string is displaced (stretched) by the greatest amount, its potential energy is maximized , just as in the case of a spring.
(B) At zero displacement, the string is like a spring at its equilibrium position. Therefore, the potential energy of the string is at a minimum.
Chapter 14 Waves and Sounds Q.89GP
Solution:
Chapter 14 Waves and Sounds Q.90GP
You stand near the tracks as a train approaches with constant speed. The train is operating its horn continuously, and you listen carefully to the sound it makes. For each of the following properties of the sound, state whether it increases, decreases, or stays the same as the train gets closer: (a) the intensity; (b) the frequency; (c) the wavelength; (d) the speed.
Solution:
Chapter 14 Waves and Sounds Q.91GP
Sitting peacefully in your living room one stormy day, you see a flash of lightning through the windows. Eight and a half seconds later thunder shakes the house. Estimate the distance from your house to the bolt of lightning.
Solution:
Chapter 14 Waves and Sounds Q.92GP
The fundamental of an organ pipe that is closed at one end and open at the other end is 261.6 Hz (middle C). The second harmonic of an organ pipe that is open at both ends has the same frequency. What are the lengths of these two pipes?
Solution:
Chapter 14 Waves and Sounds Q.93GP
The Loudest Animal The loudest sound produced by a living organism on Earth is made by the bowhead whale (Balaam mysticetus). These whales can produce a sound that, if heard in air at a distance of 3.00 m, would have an intensity level of 127 dB. This is roughly the equivalent of 5000 trumpeting elephants. How far away can you be from a 127-dB sound and still just barely hearit?(Assume a point source, and ignore reflections and absorption.)
Solution:
Chapter 14 Waves and Sounds Q.94GP
Hearing a Good Hit Physicist Robert Adair, once appointed the “official physicist to the National League” by the commissioner of baseball, believes that the “crack of the bat” can tell an outfielder how well the ball has been hit. According to Adah”, a good hit makes a sound of 510 Hz, while a poor hit produces a sound of 170 Hz. What is the difference in wavelength of these sounds?
Solution:
Chapter 14 Waves and Sounds Q.95GP
A standing wave of 603 Hz is produced on a string that is 1.33 m long and fixed on both ends. If the speed of waves on this string is 402 m/s, how many antinodes are there in the standing wave?
Solution:
Chapter 14 Waves and Sounds Q.96GP
Measuring Hearing Loss To determine the amountof temporary hearing loss load music can cause in humans, researchers studied a group of 20 aduit females who were exposed to 110-dB music far60 minutes. Eleven of the 20 subjects showed a 20.0-dB reduction in hearing sensitivity at 4000 Hz, What is the intensity corresponding to the threshold of hearing for these subjects?
Solution:
Chapter 14 Waves and Sounds Q.97GP
Hearing a Pin Drop The ability to hear a “pin drop” is the sign of sensitive hearing. Suppose a 0,55-g pin is dropped from a height of 28 cm, and that the pin emits sound for 1.5 s when it lands. Assuming all of the mechanical energy of the pin is converted to sound energy, and that the sound radiates uniformly in all directions, find the maximum distance from which a person can hear the pin drop. (This is the ideal maximum distance, but atmospheric absorption and other factors will make the actual maximum distance considerably smaller.)
Solution:
The relation between mechanical energy and power is,
Chapter 14 Waves and Sounds Q.98GP
A machineshop has 120 equally noisy machines that together produce an intensity level of 92 dB. If the intensity level must be reduced to 82 dB, how many machines must be turned off?
Solution:
Chapter 14 Waves and Sounds Q.99GP
When you blow across the top of a soda pop bottle you hear a fundamental frequency of 206 Hz. Suppose the bottle is now filled with helium, (a) Does the fundamental frequency increase, decrease, or stay the same? Explain, (b) Find the new fundamental frequency. (Assume that the speed of sound in helium is three times that in air.)
Solution:
Chapter 14 Waves and Sounds Q.100GP
Speed of a Tsunami Tsunamis can have wavelengths between 100 and 400 km. Since this is much greater than the average depth of the oceans (about 4.3 km), the ocean can be considered as shallow water for these waves. Using the speed of waves in shallow water of depth d given in Problem, find the typical speed for a tsunami. (Note: In the open ocean, tsunamis generally have an amplitude of less than a meter, allowing them to pass ships unnoticed. As they approach shore, however, the water depth decreases and the waves slow down. This can reIsuit in an increase of amplitude to as much as 37 m or more.)
Solution:
Chapter 14 Waves and Sounds Q.101GP
Two trains with 124-Hz horns approach one another. The slower of the two trams has a speed of 26 m/s. What is the speed of the fast train if an observer standing near the tracks between the trains hears a beat frequency of 4.4 Hz?
Solution:
Chapter 14 Waves and Sounds Q.102GP
Solution:
Chapter 14 Waves and Sounds Q.103GP
Solution:
Chapter 14 Waves and Sounds Q.104GP
Cracking Your Knuckles When you “crack” a knuckle, you cause the knuckle cavity to widen rapidly This, in turn, allows the synovial fluid to expand into a larger voluma If this expansion is
sufficiently rapid. it causes a gas bubble to form in the fluid in a process known as cavitation. This is the mechanism responsible for the cracking soundS (Cavitation can also cause pits in
rapidly rotating ship’s propellers) If a “crack” produces a sound with an intensity level of 57 dB at your ear. which is 18 cm from the knuckle, how far from your knuckle can the “crack” be heard? Assume the sound propagates uniformly in all directions, with no reflections or absorption
Solution:
A crack produces a sound with an intensity level of 57 dB at your ear which is 18 cm from the knuckle. Calculate the distance from the knuckle at which the crack can be barely heard using the expression for the sound intensity level.
Chapter 14 Waves and Sounds Q.105GP
A steel guitar string has a tension T, length L, and diameter D: Give the multiplicative factor by which the fundamental frequency of the string changes under the following conditions: (a) The tension in the suing is increased by a factor of 4. The diameter is D and the length is L. (b) The diameter of the string is increased by a factor of 3. The tension is T and the length is L. (c) The length of the string is halved. The tension is T and the diameter is D.
Solution:
Chapter 14 Waves and Sounds Q.106GP
ASlinky has a mass of 0.28 kg and negligible length. When itis stretched 1.5 m, it is found that transverse waves travel the length of the Slinky in 0.75 s. (a) What is the force constant, k, of the Slinky? (b) If the Slinky is stretched farther, will the time required for a wave to travel the length of the Slinky increase, decrease, or stay the same? Explain, (c) If the Slinky is stretched 3.0 m, how much time does it take a wave to travel the length of the Slinky? (The Slinky stretches like an ideal spring, and propagates transverse waves like a rope with variable tension.)
Solution:
Chapter 14 Waves and Sounds Q.107GP
OSHA Noise Standards OSHA, the Occupational Safety and Health Administration, has established standards for workplace exposure to noise. According to OSHA’s HearingConservation Standard, the permissible noise exposure per day is 95.0 dB for 4 hours or 105 dB for 1 hour. Assuming the eardrum is 9.5 mm in diameter, find the energy absorbed by the eardrum (a) with 95.0 dB for 4 hours and (b) with 105 dB for 1 hour, (c) Is OSHA’s safety standard simply a measure of the amount of energy absorbed by the ear? Explain.
Solution:
Chapter 14 Waves and Sounds Q.108GP
Thunders ticks at Ball Games “Thundersticks” are a popular noisemaking device at many sporting events. A typical thunderstick is a hollow plastic tube about 82 cm long and 8.5 cm in diameter. When two thundersticks are hit sharply together, they produce a copious amount of noise, (a) Which dimension, the length or diameter, is more important in determining the frequency of the sound emitted by the thundersticks? Explain, (b) Estimate the characteristic frequency of the thunders tick’s sound, (c) Suppose a single pair of thundersticks produces sound with an intensity level of 95 dB. What is the intensity level of 1200 pairs of fhundcrsticks clapping simultaneously?
Solution:
Chapter 14 Waves and Sounds Q.109GP
An organ pipe 2.5 m long is open at one end and closed at the other end. What is the linear distance between a node and the adjacent antinode for the third harmonic in this pipe?
Solution:
Chapter 14 Waves and Sounds Q.110GP
Two identical strings with the same tension vibrate at 631 Hz. Tf the tension in one of the strings is increased by 2.25%, what is the resulting beat frequency?
Solution:
Chapter 14 Waves and Sounds Q.111GP
The Sound of a Black Hole Astronomers using the Chandra X-ray Observatory have discovered that the Perseus Black Hole, some 250 million light years away, produces sound waves in the gaseous halo that surrounds it. The frequency of this sound is the same as the frequency of the 59th B-flat below the B-flat given, in Table 14-3. How long does it take for this sound wave to complete one cycle? Give your answer in years.
Solution:
Chapter 14 Waves and Sounds Q.112GP
The Love Song of the Midshipman Fish When the plain fin midshipman fish (Porichthys notatus)migrates from deep Pacific watersto the west coast of North America each summer, the males begin to sing their “love song,” which some describe as sounding like a low-pitched motorboat. Houseboat residents and shore dwellers are kept awake for nights on end by the amorous fish. The love song consists of a single note, the second A flat below middle C. (a) If the speed of sound in seawater is 1531 m/s, what is the wavelength of the midshipman’s song? (b) What is the wavelength of the sound after it emerges into the air? (Information on the musical scale is given in Table 14-3.)
Solution:
Chapter 14 Waves and Sounds Q.113GP
Solution:
Chapter 14 Waves and Sounds Q.114GP
Experiments on water waves show that the speed of waves in shallow water is independent of their wavelength (see Problem). Using this observation and dimensional analysis, determine how the speed v of shallow-water waves depends on the depth of the water, d, the mass per volume of water, p, and the acceleration of gravity, g.
Solution:
Chapter 14 Waves and Sounds Q.115GP
Solution:
Chapter 14 Waves and Sounds Q.116GP
Beats and Standing Waves InProblem, suppose the observer walks toward one speaker with a speed of 1.35 m/s. (a) What frequency does the observer hear from each speaker? (b) What beat frequency does the observer hear? (c) How far must the observer walk to go from one point of constructive interference to the next? (d) How many times per second does the observer hear maximum loudness from the speakers? Compare your result with the beat frequency from part (b).
Solution:
Chapter 14 Waves and Sounds Q.117PP
Modern-day animals make extensive use of sounds in their interactions with others. Some sounds are meant primarily for members of the same species, like the cooing calls of a pair of doves, the long-range infrasoimd communication between elephants, or the songs of the hump-backed whale. Other sounds may be used as a threat to other species, such as the Tattle of a rattlesnake or the roar of a lion.
There is little doubt that extinct animals used sounds in much the same ways. But how can we ever hear the call of a long-vanished animal like a dinosaur when sounds don’t fossilize? In some cases, basic physics may have the answer.
Consider, for example, the long-crested, duck-billed dinosaur Parasaurohplus walkeri, which roamed the Earth 75 million years ago. This dinosaur possessed the largest crest of any duck bill—so long, in fact, that there was a notch in P. walker’s spine to make room for the crest when its head was tilted backward. Many paleontologists believe the air passages in the dinosaur’s crest acted like bent organ pipes open at both ends, and that they produced sounds P. walkeri used to communicate with others of its kind. As air was forced through the passages, the predominant sound they produced would be the fundamental standing wave, with a small admixture of higher harmonics as well. The frequencies of these standing waves can be determined with basic physical principles. Figure 14-43 presents a plot of the lowest ten harmonics of a pipe that is open at both ends as a function of the length of the pipe.
Solution:
Chapter 14 Waves and Sounds Q.118PP
Modern-day animals make extensive use of sounds in their interactions with others. Some sounds are meant primarily for members of the same species, like the cooing calls of a pair of doves, the long-range infrasoimd communication between elephants, or the songs of the hump-backed whale. Other sounds may be used as a threat to other species, such as the Tattle of a rattlesnake or the roar of a lion.
There is little doubt that extinct animals used sounds in much the same ways. But how can we ever hear the call of a long-vanished animal like a dinosaur when sounds don’t fossilize? In some cases, basic physics may have the answer.
Consider, for example, the long-crested, duck-billed dinosaur Parasaurohplus walkeri, which roamed the Earth 75 million years ago. This dinosaur possessed the largest crest of any duck bill—so long, in fact, that there was a notch in P. walker’s spine to make room for the crest when its head was tilted backward. Many paleontologists believe the air passages in the dinosaur’s crest acted like bent organ pipes open at both ends, and that they produced sounds P. walkeri used to communicate with others of its kind. As air was forced through the passages, the predominant sound they produced would be the fundamental standing wave, with a small admixture of higher harmonics as well. The frequencies of these standing waves can be determined with basic physical principles. Figure 14-43 presents a plot of the lowest ten harmonics of a pipe that is open at both ends as a function of the length of the pipe.
Solution:
Chapter 14 Waves and Sounds Q.119PP
Modern-day animals make extensive use of sounds in their interactions with others. Some sounds are meant primarily for members of the same species, like the cooing calls of a pair of doves, the long-range infrasoimd communication between elephants, or the songs of the hump-backed whale. Other sounds may be used as a threat to other species, such as the Tattle of a rattlesnake or the roar of a lion.
There is little doubt that extinct animals used sounds in much the same ways. But how can we ever hear the call of a long-vanished animal like a dinosaur when sounds don’t fossilize? In some cases, basic physics may have the answer.
Consider, for example, the long-crested, duck-billed dinosaur Parasaurohplus walkeri, which roamed the Earth 75 million years ago. This dinosaur possessed the largest crest of any duck bill—so long, in fact, that there was a notch in P. walker’s spine to make room for the crest when its head was tilted backward. Many paleontologists believe the air passages in the dinosaur’s crest acted like bent organ pipes open at both ends, and that they produced sounds P. walkeri used to communicate with others of its kind. As air was forced through the passages, the predominant sound they produced would be the fundamental standing wave, with a small admixture of higher harmonics as well. The frequencies of these standing waves can be determined with basic physical principles. Figure 14-43 presents a plot of the lowest ten harmonics of a pipe that is open at both ends as a function of the length of the pipe.
Solution:
Chapter 14 Waves and Sounds Q.120PP
Modern-day animals make extensive use of sounds in their interactions with others. Some sounds are meant primarily for members of the same species, like the cooing calls of a pair of doves, the long-range infrasoimd communication between elephants, or the songs of the hump-backed whale. Other sounds may be used as a threat to other species, such as the Tattle of a rattlesnake or the roar of a lion.
There is little doubt that extinct animals used sounds in much the same ways. But how can we ever hear the call of a long-vanished animal like a dinosaur when sounds don’t fossilize? In some cases, basic physics may have the answer.
Consider, for example, the long-crested, duck-billed dinosaur Parasaurohplus walkeri, which roamed the Earth 75 million years ago. This dinosaur possessed the largest crest of any duck bill—so long, in fact, that there was a notch in P. walker’s spine to make room for the crest when its head was tilted backward. Many paleontologists believe the air passages in the dinosaur’s crest acted like bent organ pipes open at both ends, and that they produced sounds P. walkeri used to communicate with others of its kind. As air was forced through the passages, the predominant sound they produced would be the fundamental standing wave, with a small admixture of higher harmonics as well. The frequencies of these standing waves can be determined with basic physical principles. Figure 14-43 presents a plot of the lowest ten harmonics of a pipe that is open at both ends as a function of the length of the pipe.
Solution:
Due to the change in length of the tube from 1.5m to 2.7m, the standing wave frequency decreases. The change in fundamental frequency would be less than the change in second harmonic frequency.
Chapter 14 Waves and Sounds Q.121IP
Suppose the engineer adjusts the speed of the trainuntil the sound he hears reflected from the cliff is 775 Hz. The train’s whistle still produces a tone of 650.0 Hz. (a) Is the new speed of the train greater than, less than, or equal to 21.2 m/s? Explain, (b) Find the new speed of the train.
Solution:
Chapter 14 Waves and Sounds Q.122IP
Suppose the train is backing away from the cliff with a speed of 18.5 m/s and is sounding its 650.0-Hz whistle, (a) What is the frequency heard by the observer standing near the runnel entrance? (b) What is the frequency heard by the engineer?
Solution:
Chapter 14 Waves and Sounds Q.123IP
Suppose we add more water to the soda pop bottle, (a) Does the fundamental frequency increase, decrease, or stay the same? Explain, (b) Find the fundamental frequency if the height of water in the bottle is increased to 7.5 cm. The height of the bottle is still 26.0 cm.
Solution:
Chapter 14 Waves and Sounds Q.124IP
The speed of sound increases slightly withtemperature, (a) Does the fundamental frequency of the bottle increase, decrease, or stay the same as the air heats up on a warm day? Explain, (b) Find the fundamental frequency if the speed of sound in air increases to 348 m/s. Assume the bottle is 26.0 cm tall, and that it contains water to a depth of 6.5 cm.
Solution:
a) The speed of sound in air increases with increase in temperature. This can be observed from the table 14-1 in the text book. The frequency of sound wave in air is directly proportional to the speed of the sound in air. When speed of the sound waves decreases due to increase in temperature, then frequency of the sound wave also increases.
