Answer: (a) Find the speed of waves on a violin string of

In a first expeliment, a sinusoidal sound wave is sent through a long tube of air, transporting energy at the average rate of Pavg,I' In a second experiment, two other sound waves, identical to the first one, are to be sent simultaneously through the tube with a phase difference of either 0, 0.2 wavelength, or 0.5 wavelength between the waves. (a) With only mental calculation, rank those choices of according to the average rate at which the waves will transport energy, greatest first. (b) For the first choice of , what is the average rate in terms of P avg,l?

In Fig. 17-24, two point sources SI and Sz, wIDch are in phase, emit identical sound waves of wavelength 2.0 m. In terms of wavelengths, what is the phase difference between the waves arriving at point P if (a) Lj = 38 m and L2 = 34 m, and (b) Lj = 39 m and L2 = 36 m? (c) Assuming that the source separation is much smaller than Ll and L 2, what type of interference occurs at P in situations (a) and (b)?

In Fig, 17-25, three long tubes (A, B, and C) are filled with different gases under different pressures. The ratio of the bulk modulus to the density is indicated for each gas in terms of a basic value Bo/Po. Each tube has a piston at its left end that can send a sound pulse through the tube (as in Fig, 16-2). The three pulses are sent simultaneously. Rank the tubes according to the time of arrival of the pulses at the open right ends of the tubes, earliest first.

The sixth harmonic is set up in a :~L--:-L~: I I I pipe. (a) How many open ends does Fig. 17-25 Question 3. the pipe have (it has at least one)? (b) Is there a node, antinode, or some intermediate state at the midpoint?

In Fig. 17-26, pipe A is made to oscillate in its third harmonic by a small internal sound source. Sound emitted at the right end happens to resonate four nearby pipes, each with only one open end (they are not drawn to scale). Pipe B oscillates in its lowest harmonic, pipe C in its second lowest harmonic, pipe D in its third lowest harmonic, and pipe E in its fourth lowest harmonic, Without -A-l)) __ ------'I B __ ------'I c __ ------'I D ___ --'IE Fig. 17-26 Question 5. QUESTIONS 467 computation, rank all five pipes according to their length, greatest first. (Hint: Draw the standing waves to scale and then draw the pipes to scale.)

Pipe A has length L and one open end. Pipe B has length 2L and two open ends. Which harmonics of pipe B have a frequency that matches a resonant frequency of pipe A?

Figure 17-27 shows a moving sound source S that emits at a certain frequency, and four stationary sound detectors. Rank the detectors according to the frequency of the sound they detect from the source, greatest first.

A friend rides, in turn, the rims of three fast merry-go-rounds while holding a sound source that emits isotropically at a certain frequency, You stand far from each merry-go-round. The frequency you hear for each of your friend's three rides varies as the merry-goround rotates. The variations in frequency for the three rides are given by the three curves in Fig. 17-28. Rank the curves according to (a) the linear speed v of the sound source, (b) the angular speeds IJ) of the merry-go-rounds, and (c) the radii r of the merry-go-rounds, greatest fil'st

For a particular tube, here are four of the six harmonic frequencies below 1000 Hz: 300, 600, 750, and 900 Hz. What two frequencies are missing from the list?

Figure 17-29 shows a stretched stJing of length L and pipes a, b, c, and d of lengths L, 2L, Ll2, and Ll2, respectively. The string's tension is adjusted until the speed of waves on the string equals the speed of sound waves in the air. The fundamental mode of oscillation is then set up on the string. In which pipe will the sound produced by the string cause resonance, and what oscillation mode will that sound set up?

Diagnostic ultrasound of frequency 4.50 MHz is used to examine tumors in soft tissue. (a) What is the wavelength in air of such a sound wave? (b) If the speed of sound in tissue is 1500 mis, what is the wavelength of this wave in tissue?

The pressure in a traveling sound wave is given by the equation t:.p = (1.50 Pa) sin 1T[(0.900 m-1)x - (315 S-l)t]. Find the (a) pressure amplitude, (b) frequency, (c) wavelength, and (d) speed of the wave.

A sound wave of the form s = Sill cos(kx - wt + ) travels at 343 mls through air in a long horizontal tube. At one instant, air molecule A at x = 2.000 m is at its maximum positive displacement of 6.00 nm and air molecule B at x = 2.070 m is at a positive displacement of 2.00 nm. All the molecules between A and B are at intermediate displacements. What is the frequency of the wave?

Figure 17-31 shows the output from a pressure monitor mounted at a point along the path taken by a sound wave of a single frequency traveling at 343 mls through air with a uniform density of 1.21 kg/m3. The vertical axis scale is set by /:"ps = 4.0 mPa. If the displacement function of the wave is sex, t) = Sill cos(kx - wt), what are (a) Sill' (b) Ie, and (c) w? The air is then cooled so that its density is 1.35 kg/m3 and the speed of a sound wave through it is 320 m/s. The sound source again emits the sound wave at the same frequency and same pressure amplitude. What now are (d) Sill' (e) Ie, and (f) w?

A handclap on stage in an amphitheater sends out sound waves that scatter from terraces of width w = 0.75 m (Fig. 17-32). The sound returns to the stage as a periodic series of pulses, one from each terrace; the parade of pulses sounds like a played note. (a) Assuming that all the rays in Fig. 17-32 are horizontal, find the frequency at which the pulses return (that is, the frequency of the perceived note). (b) If the width w of the terraces were smaller, would the frequency be higher or lower?

Tho sound waves, from two different sources with the same frequency, 540 Hz, travel in the same direction at 330 m/s. The sources are in phase. What is the phase difference of the waves at a point that is 4.40 m from one source and 4.00 m from the other?

Two loud speakers are located 3.35 m apart on an outdoor stage. A listener is 18.3 m from one and 19.5 m from the other. During the sound check, a signal generator drives the two speakers in phase with the same amplitude and frequency. The transmitted frequency is swept through the audible range (20 Hz to 20 kHz). (a) What is the lowest frequency fmin,! that gives minimum signal (destructive interference) at the listener's location? By what number must fmin,! be multiplied to get (b) the second lowest frequency fmin,2 that gives minimum signal and (c) the third lowest frequency fmin,3 that gives minimum signal? (d) What is the lowest frequency fmax,! that gives maximum signal (constructive interference) at r-L-1 the listener's location? By what A p number must fmax,! be multiplied to .- get (e) the second lowest frequency L fmax,2 that gives maximum signal and B . - _1_ (f) the third lowest frequency fmax,3 that gives maximum signal?

In Fig, 17-33, sound waves A and B, both of wavelength A, are initially in phase and traveling rightward, as indicated by the two rays. Wave A is reflected from four surfaces but ends up traveling in its original direction. Wave B ends in that direction after reflecting from two surfaces. Let distance L in the figure be expressed as a multiple q of A: L = qA. What are the (a) smallest and (b) second smallest values of q that put A and B exactly out of phase with each other after the reflections?

Figure 17-34 shows two !Ill !Ill S) l_ D _----1 S2 isotropic point sources of sound, S! r-- - l and S2' The sources emit waves in phase at wavelength 0.50 m; they are separated by D = 1.75 m, If we Fig. 17-34 Problems 19 and 105. move a sound detector along a large circle centered at the midpoint between the sources, at how many points do waves arrive at the detector (a) exactly in phase and (b) exactly out of phase?

Figure 17-35 shows four isotropic point sources of sound that are uniformly spaced on an x axis. The sources emit sound at the same wavelength A and same amplitude Sm' and they emit in phase. A point P is shown on the x axis. Assume that as the sound waves travel to P, the decrease in their amplitude is negligible. What multiple of Sill is the amplitude of the net wave at P if distance d in the figure is (a) A/4, (b) Al2, and (c) A7

In Fig. 17-36, two speakers separated by distance d! = 2.00 m are in phase. Assume the amplitudes of the sound waves from the speakers are approximately the same at the listener's ear at distance d2 = 3.75 m directly in front of one speaker. Consider the full audible p Speakers Listener range for normal hearing, 20 Hz to Fig. 17-36 Problem 21. 20 kHz. (a) What is the lowest frequency fmin,! that gives minimum signal (destructive interference) at the listener's ear? By what number must fmin I be multiplied to get (b) the second lowest frequency fmin,2 that 'gives minimum signal and (c) the third lowest frequency fmin,3 that gives minimum signal? (d) What is the lowest frequency fmaxl that gives maximum signal (constructive interference) at the list'ener's ear? By what number must fmax,) be multiplied to get (e) the second lowest frequency fmax,2 that gives maximum signal and (f) the third lowest frequency fmax,3 that gives maximum signal?

In Fig. 17-37, sound with a 40.0 cm wavelength travels rightward from a source and through a tube that consists of a straight portion and a half-circle. Part of the sound wave travels through the half-circle and then rejoins the rest of the wave, which goes directly through the straight portion. This rejoining results in interference. What is the smallest radius /' that results in an intensity minimum at the detector?

Figure 17-38 shows two )' point sources SI and S2 that emit sound of wavelength A = 2.00 m. The emissions are isotropic and in -.--+-S-'I ______ -p-x phase, and the separation between I d the sources is d = 16.0 m. At any ~ point P on the x axis, the wave from S2 S) and the wave from S2 interfere. When P is very far away (x = 00), what are (a) the phase difference Fig.17-38 Problem 23. between the arriving waves from S) and S2 and (b) the type of interference they produce? Now move point P along the x axis toward SI' (c) Does the phase difference between the waves increase or decrease? At what distance x do the waves have a phase difference of (d) 0.50.1, (e) 1.00.1, and (f) 1.50A?

Suppose that the sound level of a conversation is initially at an angry 70 dB and then drops to a soothing 50 dB. Assuming that the frequency of the sound is 500 Hz, determine the (a) initial and (b) final sound intensities and the (c) initial and (d) final sound wave amplitudes.

A sound wave of frequency 300 Hz has an intensity of 1.00 fhW/m2 What is the amplitude of the air oscillations caused by this wave?

A 1.0 W point source emits sound waves isotropically. Assuming that the energy of the waves is conserved, find the intensity (a) 1.0 m from the source and (b) 2.5 m from the source.

A certain sound source is increased in sound level by 30.0 dB. By what multiple is (a) its intensity increased and (b) its pressure amplitude increased?

Two sounds differ in sound level by 1.00 dB. What is the ratio of the greater intensity to the smaller intensity?

A source emits sound waves isotropically. The intensity of the waves 2.50 m from the source is 1.91 X 10-4 W/m2. Assuming that the energy of the waves is conserved, find the power of the source.

The source of a sound wave has a power of 1.00 fh W. If it is a point source, (a) what is the intensity 3.00 m away and (b) what is the sound level in decibels at that distance?

When you "crack" a knuckle, you suddenly widen the knuckle cavity, allowing more volume for the synovial fluid inside it and causing a gas bubble suddenly to appear in the fluid. The sudden production of the bubble, called "cavitation," produces a sound pulse-the cracking sound. Assume that the sound is transmitted uniformly in all directions and that it fully passes from the knuckle interior to the outside. If the pulse has a sound level of 62 dB at your ear, estimate the rate at which energy is produced by the cavitation.

Approximately a third of people with normal hearing have ears that continuously emit a low-intensity sound outward through the ear canal. A person with such spontaneous otoacollstic emission is rarely aware of the sound, except perhaps in a noisefree environment, but occasionally the emission is loud enough to be heard by someone else nearby. In one observation, the sound wave had a frequency of 1665 Hz and a pressure amplitude of 1.13 X 10-3 Pa. What were (a) the displacement amplitude and (b) the intensity of the wave emitted by the ear?

Male Rana catesbeiana bullfrogs are known for their loud mating call. The call is emitted not by the frog's mouth but by its eardrums, which lie on the surface of the head. And, surprisingly, the sound has nothing to do with the frog's inflated throat. If the emitted sound has a frequency of 260 Hz and a sound level of 85 dB (near the eardrum), what is the amplitude of the eardrum's oscillation? The air density is 1.21 kg/m3.

Two atmospheric sound sources A and B emit isotropically at constant power. The sound levels f3 of their emissions are plotted in Fig. 17-39 versus the radial distance r from the sources. The vertical axis scale is set by f31 = 85.0 dB and f32 = 65.0 dB. What are (a) the ratio of the larger power to the smaller power and (b) the sound level difference at r = 10 m?

A point source emits 30.0 W of sound isotropically.A small microphone intercepts the sound in an area of 0.750 cm2 , 200 m from the source. Calculate (a) the sound intensity there and (b) the power intercepted by the microphone.

Party hearing. As the number of people at a party increases, you must raise your voice for a listener to hear you against the background noise of the other partygoers. However, once you reach the level of yelling, the only way you can be heard is if you move closer to your listener, into the listener's "personal space." Model the situation by replacing you with an isotropic point source of fixed power P and replacing your listener with a point that absorbs part of your sound waves. These points are initially separated by ri = 1.20 m. If the background noise increases by D.f3 = 5 dB, the sound level at your listener must also increase. What separation rf is then required?

A sound source sends a sinusoidal sound wave of angular frequency 3000 rad/s and amplitude 12.0 nm through a tube of air. The internal radius of the tube is 2.00 cm. (a) What is the average rate at which energy (the sum of the kinetic and potential energies) is transported to the opposite end of the tube? (b) If, simultaneously, an identical wave travels along an adjacent, identical tube, what is the total average rate at which energy is transported to the opposite ends of the two tubes by the waves? If, instead, those two waves are sent along the same tube simultaneously, what is the total average rate at which they transport energy when their phase difference is (c) 0, (d) 0.401rrad, and (e) 1Trad?

The water level in a vertical glass tube 1.00 m long can be adjusted to any position in the tube. A tuning fork vibrating at 686 Hz is held just over the open top end of the tube, to set up a standing wave of sound in the air-filled top portion of the tube. (That air filled top portion acts as a tube with one end closed and the other end open.) (a) For how many different positions of the water level will sound from the fork set up resonance in the tube's air-filled portion, which acts as a pipe with one end closed (by the water) and the other end open? What are the (b) least and (c) second least water heights in the tube for resonance to occur?

(a) Find the speed of waves on a violin string of mass 800 mg and length 22.0 cm if the fundamental frequency is 920 Hz. (b) What is the tension in the string? For the fundamental, what is the wavelength of (c) the waves on the string and (d) the sound waves emitted by the string?

Organ pipe A, with both ends open, has a fundamental frequency of 300 Hz. The third harmonic of organ pipe B, with one end open, has the same frequency as the second harmonic of pipe A. How long are (a) pipe A and (b) pipe B?

A violin string 15.0 cm long and fixed at both ends oscillates in its n = 1 mode. The speed of waves on the string is 250 mis, and the speed of sound in air is 348 m/s. What are the (a) frequency and (b) wavelength of the emitted sound wave?

A sound wave in a fluid medium is reflected at a barrier so that a standing wave is formed. The distance between nodes is 3.8 cm, and the speed of propagation is 1500 m/s. Find the frequency of the sound wave

In Fig. 17-40, S is a small loudspeaker driven by an audio oscillator with a frequency that is varied from 1000 Hz to 2000 Hz, and D is a cylindrical pipe with two open ends and a length of 45.7 cm. The speed of sound in the air-filled pipe is 344 mls. (a) At how many frequencies does the sound from the loudspeaker set up resonance in the pipe? What are the (b) lowest and (c) second lowest frequencies at which resonance occurs?

The crest of a Parasaurolophus dinosaur skull contains a nasal passage in the shape of a long, bent tube open at both ends. The dinosaur may have used the passage to produce sound by setting up the fundamental mode in it. (a) If the nasal passage in a certain Parasaul'Olophus fossil is 2.0 m long, what frequency would have been produced? (b) If that dinosaur could be recreated (as in Jurassic Park), would a person with a hearing range of 60 Hz to 20 kHz be able to hear that fundamental mode and, if so, would the sound be high or low frequency? Fossil skulls that contain shorter nasal passages are thought to be those of the female Parasaurolophus. (c) Would that make the female's fundamental frequency higher or lower than the male's?

In pipe A, the ratio of a particular harmonic frequency to the next lower harmonic frequency is 1.2. In pipe B, the ratio of a particular harmonic frequency to the next lower harmonic frequency is 1.4. How many open ends are in (a) pipe A and (b) pipe B?

Pipe A, which is 1.20 m long and open at both ends, oscillates at its third lowest harmonic frequency. It is filled with air for which the speed of sound is 343 m/s. Pipe B, which is closed at one end, oscillates at its second lowest harmonic frequency. This frequency of B happens to match the frequency of A. An x axis extends along the interior of B, with x = 0 at the closed end. (a) How many nodes are along that axis? What are the (b) smallest and (c) second smallest value of x locating those nodes? (d) What is the fundamental frequency of B?

A well with vertical sides and water at the bottom resonates at 7.00 Hz and at no lower frequency. (The air-filled portion of the well acts as a tube with one closed end and one open end.) The air in the well has a density of 1.10 kg/m3 and a bulk modulus of 1.33 X 105 Pa. How far down in the well is the water surface?

One of the harmonic frequencies of tube A with two open ends is 325 Hz. The next-highest harmonic frequency is 390 Hz. (a) What harmonic frequency is next highest after the harmonic frequency 195 Hz? (b) What is the number of this next-highest harmonic? One of the harmonic frequencies of tube B with only one open end is 1080 Hz. The next-highest harmonic frequency is 1320 Hz. (c) What harmonic frequency is next highest after the harmonic frequency 600 Hz? (d) What is the number of this next-highest harmonic?

A violin string 30.0 cm long with linear density 0.650 glm is placed near a loudspeaker that is fed by an audio oscillator of variable frequency. It is found that the string is set into oscillation only at the frequencies 880 and 1320 Hz as the frequency of the oscillator is varied over the range 500-1500 Hz. What is the tension in the string?

A tube 1.20 m long is closed at one end. A stretched wire is placed near the open end. The wire is 0.330 m long and has a mass of 9.60 g. It is fixed at both ends and oscillates in its fundamental mode. By resonance, it sets the air column in the tube into oscillation at that column's fundamental frequency. Find (a) that frequency and (b) the tension in the wire.

The A string of a violin is a little too tightly stretched. Beats at 4.00 per second are heard when the string is sounded together with a tuning fork that is oscillating accurately at concert A (440 Hz). What is the period of the violin string oscillation?

A tuning fork of unknown frequency makes 3.00 beats per second with a standard fork of frequency 384 Hz. The beat frequency decreases when a small piece of wax is put on a prong of the first fork. What is the frequency of this fork?

Two identical piano wires have a fundamental frequency of 600 Hz when kept under the same tension. What fractional increase in the tension of one wire will lead to the occurrence of 6.0 beatsls when both wires oscillate simultaneously?

You have five tuning forks that oscillate at close but different frequencies. What are the (a) maximum and (b) minimum number of different beat frequencies you can produce by sounding the forks two at a time, depending on how the frequencies differ?

A whistle of frequency 540 Hz moves in a circle of radius 60.0 cm at an angular speed of 15.0 rad/s. What are the (a) lowest and (b) highest frequencies heard by a listener a long distance away, at rest with respect to the center of the circle?

An ambulance with a siren emitting a whine at 1600 Hz overtakes and passes a cyclist pedaling a bike at 2.44 mls. After being passed, the cyclist hears a frequency of 1590 Hz. How fast is the ambulance moving?

A state trooper chases a speeder along a straight road; both vehicles move at 160 kmlh. The siren on the trooper's vehicle produces sound at a frequency of 500 Hz. What is the Doppler shift in the frequency heard by the speeder?

A sound source A and a reflecting surface B move directly toward each other. Relative to the air, the speed of source A is 29.9 mis, the speed of surface B is 65.8 mis, and the speed of sound is 329 m/s. The source emits waves at frequency 1200 Hz as measured in the source frame. In the reflector frame, what are the (a) frequency and (b) wavelength of the arriving sound waves? In the source frame, what are the (c) frequency and (d) wavelength of the sound waves reflected back to the source?

In Fig. 17-41, a French submarine and a US. submarine move toward each other during maneuvers in motionless water in the North Atlantic. The French sub moves at speed VF = 50.00 kmlh, and the US. sub at Vus = 70.00 km/h. The French sub sends out a sonar signal (sound wave in water) at 1.000 X 103 Hz. Sonar waves travel at 5470 km/h. (a) What is the signal's frequency as detected by the US. sub? (b) What frequency is detected by the French sub in the signal reflected back to it by the US. sub?

A stationary motion detector sends sound waves of frequency 0.150 MHz toward a truck approaching at a speed of 45.0 mls. What is the frequency of the waves reflected back to the detector?

A bat is flitting about in a cave, navigating via ultrasonic bleeps. Assume that the sound emission frequency of the bat is 39 000 Hz. During one fast swoop directly toward a flat wall surface, the bat is moving at 0.025 times the speed of sound in air. What frequency does the bat hear reflected off the wall?

Figure 17-42 shows 1[:::== four tubes with lengths 1.0 m 2::::::::::::== or 2.0 m, with one or two [===== 31 open ends as drawn. The third harmonic is set up in 4 ===== 0-- D each tube, and some of the Fig. 17-42 Problem 62. sound that escapes from them is detected by detector D, which moves directly away from the tubes. In terms of the speed of sound v, what speed must the detector have such that the detected frequency of the sound from (a) tube 1, (b) tube 2, (c) tube 3, and (d) tube 4 is equal to the tube's fundamental frequency?

An acoustic burglar alarm consists of a source emitting waves of frequency 28.0 kHz. What is the beat frequency between the source waves and the waves reflected from an intruder walking at an average speed of 0.950 m/s directly away from the alarm?

A stationary detector measures the frequency of a sound source that first moves at constant velocity directly toward the detector and then (after passing the detector) directly away from it. The emitted frequency is f. During the approach the detected frequency is f~pp and during the recession it is f~ec' If (f~pp - f~ec)lf = 0.500, what is the ratio vslv of the speed of the source to the speed of sound?

A 2000 Hz siren and a civil defense official are both at rest with respect to the ground. What frequency does the official hear if the wind is blowing at 12 m/s (a) from source to official and (b) from official to source?

Two trains are traveling toward each other at 30.5 m/s relative to the ground. One train is blowing a whistle at 500 Hz. (a) What frequency is heard on the other train in still air? (b) What frequency is heard on the other train if the wind is blowing at 30.5 mls toward the whistle and away from the listener? (c) What frequency is heard if the wind direction is reversed?

A girl is sitting near the open window of a train that is moving at a velocity of 10.00 m/s to the east. The girl's uncle stands near the tracks and watches the train move away. The locomotive whistle emits sound at frequency 500.0 Hz. The air is still. (a) What frequency does the uncle hear? (b) What frequency does the girl hear? A wind begins to blow from the east at 10.00 mls. (c) What frequency does the uncle now hear? (d) What frequency does the girl now hear?

A girl is sitting near the open window of a train that is moving at a velocity of 10.00 m/s to the east. The girl's uncle stands near the tracks and watches the train move away. The locomotive whistle emits sound at frequency 500.0 Hz. The air is still. (a) What frequency does the uncle hear? (b) What frequency does the girl hear? A wind begins to blow from the east at 10.00 mls. (c) What frequency does the uncle now hear? (d) What frequency does the girl now hear?

A jet plane passes over you at a height of 5000 m and a speed of Mach 1.5. (a) Find the Mach cone angle (the sound speed is 331 mls). (b) How long after the jet passes directly overhead does the shock wave reach you?

A plane flies at 1.25 times the speed of sound. Its sonic boom reaches a man on the ground 1.00 min after the plane passes directly overhead. What is the altitude of the plane? Assume the speed of sound to be 330 m/s.

At a distance of 10 km, a 100 Hz horn, assumed to be an isotropic point source, is barely audible. At what distance would it begin to cause pain?

A bullet is fired with a speed of 685 m/s. Find the angle made by the shock cone with the line of motion of the bullet.

A sperm whale (Fig. 17-43a) vocalizes by producing a series of clicks. Actually, the whale makes only a single sound near the front of its head to start the series. Part of that sound then emerges from the head into the water to become the first click of the series. The rest of the sound travels backward through the spermaceti sac (a body of fat), reflects from the frontal sac (an air layer), and then travels forward through the spermaceti sac. When it reaches the distal sac (another air layer) at the front of the head, some of the sound escapes into the water to form the second click, and the rest is sent back through the spermaceti sac (and ends up forming later clicks). Figure 17 -43b shows a strip-chart recording of a series of clicks. A unit time interval of 1.0 ms is indicated on the chart. Assuming that the speed of sound in the spermaceti sac is 1372 mis, find the length of the spermaceti sac. From such a calculation, marine scientists estimate the length of a whale from its click series.

The average density of Earth's crust 10 km beneath the continents is 2.7 g/cm3 The speed of longitudinal seismic waves at that depth, found by timing their arrival from distant earthquakes, is 5.4 km/s. Use this information to find the bulk modulus of Earth's crust at that depth. For comparison, the bulk modulus of steel is about 16 X 1010 Pa

A certain loudspeaker system emits sound isotropically with a frequency of 2000 Hz and an intensity of 0.960 mW/m2 at a distance of 6.10 m. Assume that there are no reflections. (a) What is the intensity at 30.0 m? At 6.10 m, what are (b) the displacement amplitude and (c) the pressure amplitude?

Find the ratios (greater to smaller) of the (a) intensities, (b) pressure amplitudes, and (c) particle displacement amplitudes for two sounds whose sound levels differ by 37 dB.

In Fig. 17-44, sound waves A and B, both of wavelength A, are initially in phase and traveling right- A ward, as indicated by the two rays. __ --"I-.. Wave A is reflected from four surfaces but ends up traveling in its original direction. What multiple of wavelength A is the smallest value of distance L in the figure that puts A and B exactly out of phase with each other after the reflections?

A trumpet player on a moving Fig. 17-44 Problem 77. railroad flatcar moves toward a second trumpet player standing alongside the track while both play a 440 Hz note. The sound waves heard by a stationary observer between the two players have a beat frequency of 4.0 beats/s. What is the flatcar's speed?

In Fig. 17-45, sound of wavelength 0.850 m is emitted isotropically by point source S. Sound ray 1 extends directly to detector D, at distance L = 10.0 m. Sound ray 2 extends to D via a reflection (effectively, a "bouncing") of the sound at a flat surface. That reflection occurs on a perpendicular bisector to the SD line, at distance d from the line. Assume that the reflection shifts the sound wave by 0.500A. For what least value of d (other than zero) do the direct sound and the reflected sound arrive at D (a) exactly out of phase and (b) exactly in phase?

A detector initially moves at constant velocity directly toward a stationalY sound source and then (after passing it) directly from it. The emitted frequency is f During the approach the detected frequency is f~pp and during the recession it is f;ec' If the frequencies are related by (f~pp - f;ec)lf = 0.500, what is the ratio v Dlv of the speed of the detector to the speed of sound?

(a) If two sound waves, one in air and one in (fresh) water, are equal in intensity and angular frequency, what is the ratio of the pressure amplitude of the wave in water to that of the wave in air? Assume the water and the air are at 20e. (See Table 14-1.) (b) If the pressure amplitudes are equal instead, what is the ratio of the intensities of the waves?

A continuous sinusoidal longitudinal wave is sent along a very long coiled spring from an attached oscillating source. The wave travels in the negative direction of an x axis; the source frequency is 25 Hz; at any instant the distance between successive points of maximum expansion in the spring is 24 cm; the maximum longitudinal displacement of a spring particle is 0.30 cm; and the particle at x = 0 has zero displacement at time t = O. If the wave is written in the form sex, t) = Sm cos(kx wt), what are (a) Sm' (b) k, (c) w, (d) the wave speed, and (e) the correct choice of sign in front of w?

Ultrasound, which consists of sound waves with frequencies above the human audible range, can be used to produce an image of the interior of a human body. Moreover, ultrasound can be used to measure the speed of the Incident ~ltras~~~ ~ i ~.;;~~;18. ';;1 blood in the body; it does so by Fig. 17-46 Problem 83. comparing the frequency of the ultrasound sent into the body with the frequency of the ultrasound reflected back to the body's surface by the blood. As the blood pulses, this detected frequency varies. Suppose that an ultrasound image of the arm of a patient shows an artery that is angled at () = 20 to the ultrasound's line of travel (Fig. 17-46). Suppose also that the frequency of the ultrasound reflected by the blood in the artery is increased by a maximum of 5495 Hz from the original ultrasound frequency of 5.000 000 MHz. (a) In Fig. 17-46, is the direction of the blood flow rightward or leftward? (b) The speed of sound in the human arm is 1540 m/s. What is the maximum speed of the blood? (Hint: The Doppler effect is caused by the component of the blood's velocity along the ultrasound's direction of travel.) (c) If angle (}were greater, would the reflected frequency be greater or less?

The speed of sound in a certain metal is vm One end of a long pipe of that metal of length L is struck a hard blow. A listener at the other end hears two sounds, one from the wave that travels along the pipe's metal wall and the other from the wave that travels through the air inside the pipe. (a) If v is the speed of sound in air, what is the time intervall:::.t between the arrivals of the two sounds at the listener's ear? (b) If I:::.t = 1.00 sand the metal is steel, what is the length L?

An avalanche of sand along some rare desert sand dunes can produce a booming that is loud enough to be heard 10 km away. The booming apparently results from a periodic oscillation of the sliding layer of sand-the layer's thickness expands and contracts. If the emitted frequency is 90 Hz, what are (a) the period of the thickness oscillation and (b) the wavelength of the sound?

A sound source moves along an x axis, between detectors A and B. The wavelength of the sound detected at A is 0.500 that of the sound detected at B. What is the ratio vJv of the speed of the source to the speed of sound?

A siren emitting a sound of frequency 1000 Hz moves away from you toward the face of a cliff at a speed of 10 m/s. Take the speed of sound in air as 330 m/s. (a) What is the frequency of the sound you hear coming directly from the siren? (b) What is the frequency of the sound you hear reflected off the cliff? (c) What is the beat frequency between the two sounds? Is it perceptible (less than 20 Hz)?

At a certain point, two waves produce pressure variations given by LlPI = LlPIIl sin wt and Llpz = LlPIIl sin(wt - ).At this point, what is the ratio LlPrILlPIIl' where LlPr is the pressure amplitude of the resultant wave, if is (a) 0, (b) '1T12, (c) '1T13, and (d) '1T14?

Two sound waves with an amplitude of 12 nm and a wavelength of 35 cm travel in the same direction through a long tube, with a phase difference of '1T13 rad. What are the (a) amplitude and (b) wavelength of the net sound wave produced by their interference? If, instead, the sound waves travel through the tube in opposite directions, what are the (c) amplitude and (d) wavelength of the net wave?

A sinusoidal sound wave moves at 343 mls through air in the positive direction of an x axis. At one instant, air molecule A is at its maximum displacement in the negative direction of the axis while air molecule B is at its equilibrium position. The separation between those molecules is 15.0 cm, and the molecules between A and B have intermediate displacements in the negative direction of the axis. (a) What is the frequency of the sound wave? In a similar arrangement, for a different sinusoidal sound wave, air molecule C is at its maximum displacement in the positive direction while molecule D is at its maximum displacement in the negative direction. The separation between the molecules is again 15.0 cm, and the molecules between C and D have intermediate displacements. (b) What is the frequency of the sound wave?

Two identical tuning forks can oscillate at 440 Hz. A person is located somewhere on the line between them. Calculate the beat frequency as measured by this individual if (a) she is standing still and the tuning forks move in the same direction along the line at 3.00 mis, and (b) the tuning forks are stationary and the listener moves along the line at 3.00 m/s.

You can estimate your distance from a lightning stroke by counting the seconds between the flash you see and the thunder you later hear. By what integer should you divide the number of seconds to get the distance in kilometers?

Figure 17-47 shows an air-filled, acoustic interferometer, used to demonstrate the interference of sound waves. Sound source S is an oscillating diaphragm; D is a sound detector, such as the ear or a microphone. Path SBD can be varied in length, but path SAD is fixed. At D, the sound wave coming along path SBD interferes with that coming along path SAD. In one demonstration, the sound intensity at D has a minimum value of 100 units at one position of the movable arm and continuously climbs to a maximum value of 900 units when that arm is shifted by 1.65 cm. Find (a) the frequency of the sound emitted by the source and (b) the ratio of the amplitude at D of the SAD wave to that of the SBD wave. (c) How can it happen that these waves have different amplitudes, considering that they originate at the same source?

On July 10, 1996, a granite block broke away from a wall in Yosemite Valley and, as it began to slide down the wall, was launched into projectile motion. Seismic waves produced by its impact with the ground triggered seismographs as far away as 200 km. Later measurements indicated that the block had a mass between 7.3 X 107 kg and 1.7 X 108 kg and that it landed 500 m vertically below the launch point and 30 m horizontally from it. (The launch angle is not known.) (a) Estimate the block's kinetic energy just before it landed. Consider two types of seismic waves that spread from the impact point-a hemispherical body wave traveled through the ground in an expanding hemisphere and a cylindrical swjace wave traveled along the ground in an expanding shallow vertical cylinder (Fig. 17-48). Assume that the impact lasted 0.50 s, the vertical cylinder had a depth d of 5.0 m, and each wave type received 20% of the energy the block had just before impact. Neglecting any mechanical energy loss the waves experienced as they traveled, determine the intensities of (b) the body wave and (c) the surface wave when they reached a seismograph 200 km away. (d) On the basis of these results, which wave is more easily detected on a distant seismograph?

The sound intensity is 0.0080 W/mz at a distance of 10 m from an isotropic point source of sound. (a) What is the power of the source? (b) What is the sound intensity 5.0m from the source? (c) What is the sound level 10 m from the source?

Four sound waves are to be sent through the same tube of air, in the same direction: SI(X, t) = (9.00 nm) cos(2m - 700'1Tt) sz(x, t) = (9.00 nm) cos(2m - 700'1Tt + 0.7'1T) S3(X, t) = (9.00 nm) cos(2m - 700'1Tt + '1T) S4(X, t) = (9.00 nm) cos(2m - 700'1Tt + 1.7 '1T). What is the amplitude of the resultant wave? (Hint: Use a phasor diagram to simplify the problem.)

Straight line AB connects two point sources that are 5.00 m apart, emit 300 Hz sound waves of the same amplitude, and emit exactly out of phase. (a) What is the shortest distance between the midpoint of AB and a point on AB where the interfering waves cause maximum oscillation of the air molecules? What are the (b) second and (c) third shortest distances?

A point source that is stationary on an x axis emits a sinusoidal sound wave at a frequency of 686 Hz and speed 343 m/s. The wave travels radially outward from the source, causing air molecules to oscillate radially inward and outward. Let us define a wavefront as a line that connects points where the air molecules have the maximum, radially outward displacement. At any given instant, the wavefronts are concentric circles that are centered on the source. (a) Along x, what is the adjacent wavefront separation? Next, the source moves along x at a speed of 110 m/s. Along x, what are the wavefront separations (b) in front of and (c) behind the source?

You are standing at a distance D from an isotropic point source of sound. You walk 50.0 m toward the source and observe that the intensity of the sound has doubled. Calculate the distance D.

Pipe A has only one open end; pipe B is four times as long and has two open ends. Of the lowest 10 harmonic numbers n B of pipe B, what are the (a) smallest, (b) second smallest, and (c) third smallest values at which a harmonic frequency of B matches one of the harmonic frequencies of A ?

A pipe 0.60 m long and closed at one end is filled with an unknown gas. The third lowest harmonic frequency for the pipe is 750 Hz. (a) What is the speed of sound in the unknown gas? (b) What is the fundamental frequency for this pipe when it is filled with the unknown gas?

A sound wave travels out uniformly in all directions from a point source. (a) Justify the following expression for the displacePROB LEMS 475 ment s of the transmitting medium at any distance I' from the source: s = ~ sin k(r - vt), r where b is a constant. Consider the speed, direction of propagation, periodicity, and intensity of the wave. (b) What is the dimension of the constant b?

A police car is chasing a speeding Porsche 911. Assume that the Porsche's maximum speed is 80.0 mls and the police car's is 54.0 m/s. At the moment both cars reach their maximum speed, what frequency will the Porsche driver hear if the frequency of the police car's siren is 440 Hz? Take the speed of sound in air to be 340 m/s.

Suppose a spherical loudspeaker emits sound isotropically at 10 W into a room with completely absorbent walls, floor, and ceiling (an anechoic chamber). (a) What is the intensity of the sound at distance d = 3.0 m from the center of the source? (b) What is the ratio of the wave amplitude at d = 4.0 m to that at d = 3.0 m?

In Fig. 17-34, S 1 and S2 are two isotropic point sources of sound. They emit waves in phase at wavelength 0.50 m; they are separated by D = 1.60 m. If we move a sound detector along a large circle centered at the midpoint between the sources, at how many points do waves arrive at the detector (a) exactly in phase and (b) exactly out of phase?