What is the evidence that sound tra8om4r lio. *dkcb0tg 1vels as a wave?

What is the evidence that sound is a form of energyzjzqss 4be sca2*z4-0?

Children sometimes play with o6v4j, wz(q :zb dlp,ra homemade “telephone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly hoz6orq,,z(b4 vw :dj lpw the sound wave travels from one cup to the other.

When a sound wave passes from air into waniwjc i(q4rh( 5*1uf oter, do you expect the frequency or wavelength t5f n(jqu(hwcii14 o*r o change?

What evidence can you g3-rm xd4ype v, .c.ql+y hzo.pive that the speed of sound in air does not depend signifiroly+,e.p zchy.xm.d -qp3v 4cantly on frequency?

The voice of a person who has inhaled hebr kq7kc3v61x lium sounds very high-pitched. Why?

How will the air temperature in a room affec9mfn4 kfxa,c0p tv: ako/5xn4u67n yet the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce thm. xlq7 qiya wi4++j/je amplitude of sounds inyilq+jqi4+xa / j7wm. various frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you mov zoizbev5-6y/ on27 oee up the fingerboard towardo2b oy/zon5e6vz i7-e the bridge?

A noisy truck approachehd o*.3+l7iqk b* kas7e(uyb is you from behind a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more ody ke(*3*7q.auh ikibls+7obf the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference uzj w71mlv ;2kn(q sp6in space,” whereas beats can be said to be due to “2snqj w 67p(ukml;1 zvinterference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were low;o*c , d. tdeanyex-p(ered, would the points D and C (where des;o (enace,-y xt *d.pdtructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who ez y)u,49y: csqqdub) work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technolz, yyebq49) squ du:c)ogy, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought of as a et mjb3mjvb0/+,kscl,p 7z ,5 e:gsxpsuperposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the mj,c 7/03psg+ ze kest,: ,l vbbjx5pmtwo component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer m.:jw2qj uggy2ove in the same direction, wi j ggjy2:.u2wqth the same velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound heard by a pyvno ul 31q*a7erson at nl3q*avou7y1rest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motioov2ufl6d7(4hfbiad; a.q +dbn on a swing. A monitor is blowing a whistle in front of the child v;fhda b +o7lif4d.(6q aub2d on the ground. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echo o5k w0ejl 6rcl3f her shout reflected by a cliff at the far end of the lake. She elklcwr j5063hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just belod*0g: qhnk 7g40tlwjf w the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume the speed of sound in wkj4ht0f *70 gd:qlgn seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air n;(edg62; vfrypc -iy7,yxqb at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is drifting just abov ycxa s7h3(ro*e a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the hc3 *r7a(yxo sbackfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes when strik28 yp gr 9wv6ogxx45/d:o pckming the water below is heard 3.5 s later. How higho6wmxgd54g 2ok /rc 98py x:pv is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strikeop83sv 1in.xj the concrete pavement. A moment lat 3vn.osi1pj8 xer two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error mad rb((nh10qfv ,es sjw;e over one mile of distance by the “5-second rule” for e;je(fw, 0 r1h b(qvssnstimating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sou-lgg ej e hngq r1.(bq27z.gfk7k*t;pnd at the pain level of 120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of a sound whose iccm2d54ag4de ntensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired gn,0+gr b(eqmsimultaneously at a certain plg m+e ,rgbnq(0ace, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain disuk2hk-lo 9q m1kn 547e)ntwcwtance from an airplane with four equally noisy jet engines is experiencing a sound level bordering on paiw7l19ewkq2 omu-hk cktn )45nn, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to fp,09/1 wbas u;ey/ha 0xacb rhave a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities ha ;/cp,a9/y10 bfw0be sauxr of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in d bl36um-ct2e normal conversation.2e-bt lu3mc6d Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the mouth. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave strb ablg+i6.* adikes an eardrum whose area is $5 \times10^{ -5} m^2$ (a) How much energy is absorbed by the eardrum per second?    $ \times10^{-12}$W (b) At this rate, how long would it take your eardrum to receive a total energy of 1.0 J?   $ \times10^{ 3}$yr

  Expensive amplifier A is r0tt fuad6 )vi9ated at 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound l6fuvt9i0 a dt)evel in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a d;evsh ox9egxhd9 4+vj(hn /t 9B meter registered 130 dB when placed 2.8 m in front of a loudspe(o9 h vhd94vex;jethns/+ g x9aker on the stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound level of 2.5y+ t( ds skt9ld hmvli,8 7fxy0u8tm30 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.s095,kmh88m vtt7(d yx3il sdy +lfut]$\approx$   

  If the amplitude of a sound wave is tripled, (a) byltkj(dw ;p :g3 what factor will the intensity increase? Increase ;:g(l w dktpj3by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but on,333 ( b7w q rg j:7gbfu)56nzpys7yozte bolne has twice the frequency of the other. What is the ratio7j(gnl q 5e3ng,fw u36t3b7y:yzbb z)7oosrp of their intensities?   

  What would be the sound level (i*iavy8 j2agz mvwf88:n dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating a 8yj*fva 8g:m8zwiav2ir molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as lou () rreihr.gpcvu9kt4z3 +j x5d as a 100-Hz tone that has a 50-dB sound level? (See Fig4x hjikp t+r(9.v)cezg ur5 3r. 12–6.)    dB

What are the lowest and highest frequencies that an ea,xxg tpk k5en5ny32r*r can detect when the sound level is 30 dB? (See Fig. 12 p5e*nk 23gn,yxrkx t5–6.)

  Your auditory system can accommodate a huge range of sound levels. W/qe eppwri)6-hat is the ratio of highest w) pri epq/-e6to lowest intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has cpqyc/k r) w6 wqsu:r-o2+pz+ a fundamental frequency of 440 Hz. The length of the vibrating portion is cqzp:/6swk2-+ow u+ crrqp )y32 cm, and it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm rq (4e x+n- l kqrl;pq2e7pdz:long. What are the fundamental and first three audible overtones if the pi:4 -epnd(xzlr ;7qpkeqr l+2q pe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency woul7.5n9hrfb q zld you expect from blowing across the top of an empty sod z b9l.h75fnqra bottle that is 18 cm deep, if you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pipes idxo1od .fj)gd+or0s+ - 7 tyjspanning the range of human hearing (20 Hy+x) .oo7fd+d-r1tgd j0sjo iz to 20 kHz), what would be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a .p oc5 rwp3ix*o6v+upfrequency of 540 Hz as its third harmonic. What will be its fundamental fre 5rupci .+woov*p x6p3quency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E above middle C;rpejen.0s v7i e9 i,t (330 Hz).pisv9eet7,j0ner; i .
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open or)+mplfe*kn e w2;wf8a ay.3mhgan pipe that emits middle C (262 Hz) when the tee wn ka e;p 8+*wh.)3alffmym2mperature is 21 $^{\circ} $ C.    m
(b) What are the wavelength and frequency of the fundamental standing wave in the tube?    Hz    m
(c) What are $\lambda$ and $f$in the traveling sound wave produced in the outside air?    Hz    m

  An organ is in tune at 20 h3+gf:3kddhtiu9j ip-qnc,w +0h8b i$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Example 12–10 should the hole be p(mw70uy xh xlbz(3: jthat must be uncovered to play D above middle C at 294 Hz? lpj(7z (xx0w3u:h my b   m

  (a) At T = 20 $^{\circ} $C how long must an open organ pipe be to have a fundamental frequency of 294 Hz?    m
(b) If this pipe is filled with helium, what is its fundamental frequency?   Hz

  A particular organ pipe can resonate at+:fmse5t8dnue:tq)h( h9he o 264 Hz, 440 Hz, and 616 Hz, but not at any othmh9te uqef h8+e:( ds5o) :tnher frequencies in between. (a) Show why this is an open or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at bot skg3ig( ue8/dh ends. It resonates at two successive harmonics of freu(3gsig 8/ekd quencies 275 Hz and 330 Hz. What is
(a) the fundamental frequency,    Hz
(b) the speed of sound in the gas in the tube?$\approx$    $ \times10^{2 }$ m/s

  A pipe in air at 20 ru z kwnd1;qeerm3/ r8/i+:om$^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are pres*nh7 2ubr*k hkvs6)tfj4 l g5fent within the audible range for a 2.14-m-long organ pipe atgf5h 4jf k bnvk6*)2*sru7htl 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open to thik 1dma7+u e:5rroygt 3jhm82e outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of t+o1amk8 :jmy5ru t 3g2eih7drhe standing waves in the ear canal. What is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears wpj 1wj3o zw,: df2eik v7(oy+one beat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the d,o+7o1z3w y k ewiw:pj2 (jvfother string? ±    Hz

  What is the beat frequencye4)4 xhvv he,ujh/x 2j if middle C (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operatesz;vh+ovg;.mgxy zoe :lo1 )+s at 23.5 kHz, while another (brand X) operates at an lx)+g1 o+ gsv eoz;;mzyov.h:unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with aqo lx-b9t/ez 1s y;9cj 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuni1-;/elyxzcjs ob 9q 9tng fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The ten08ocby )8acjcsion in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–130 occcjy8 8a)b.]    Hz

  How many beats will be heard if two identical flutes each try to play i.h0vzzbu2 e8middle C (262 Hz), but one is at 5.0°Cv.zzb heu2i80 and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forkx-fiz1 d5khkl4vw7 6pmz9f ,fs, A, B, and C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What51v hfmziz fxl k9 6kdfp,-47w are the possible frequencies of A and C? What beat frequencies are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A perrjam d)nun 8o().j .(pfafy/zson stands 3.00 m from one speaker and 3.508)df ja/( .por.)nnzj mfu(y a m from the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrati ucwk 2wpfpln6df 31+:ng at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are p pf fc6: u312dww+nklplayed together. (a) If one is vibrating at 132 Hz, what must be the frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound of waveleaz ; 4z7+acc*i/ev4u2t,lu,p opn bq pngths 2.64 m and 2.76 m in air. How many beats per second will;un o4z+l pte2cp/q7, zc ia,aubpv4* be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a cexl- ojf3ml-9scap- b,rtain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you ml3fml,-o9- pcb s- xjaove with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detec4h,t 1p hznc/wt if a fire engine whose siren emits at 1550 Hz movesphtn z,/1ch4w at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequencye5)* ytorvwyzq;ra*krs4 3z *mfp;p8 if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? A;8*t ;*wkzmop5sfr)y*vp 3rerq a4zyre they close? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with the same sin ui31 vl4w gq51ll+iv m(qh4ldgle frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the drivq( lv3 41im4lgvll q5du+ih w1er at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonicux(u wn3p qy;; sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the recei3 (;;nxyqpu wuved sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat emits an ulte6 +ieqeg 1miq47l. xzrasonic sound wave with frequency 30.0 kHz. What frequency does the bat he4.mq ie7 exz+1gqeil6 ar in the reflected wave?    $ \times10^{4}$ Hz

  In one of the origino0oq8csxzk6rx 8g .; hal Doppler experiments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone while at rest in the railway station. What beat o8 kx coxhq.g06; r8szfrequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses sv51*w k0bmqo3 r k;a sy1es7pultrasound waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from thmk7y 13sskvr ap0b ;o ewq1*s5e sound source?   Hz

  The Doppler effect using ultrasonic wau 9z73aqqqx ,jves of frequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequency 570 Hz. When the wind ve i tsbjdc5;e4fb 64l)bwmx0uk ( yi+w,locity is 12 m/s from the north,x4w4bifycu ,j+d50ti (); m bbswlk6e what frequency will observers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if its spe 5q5w( x1 /kdkmy7axvged at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at M4)jr -mxc, 1 mcqjxv4vach 2.3 where the speed of sound is 310 m/s (a) What is the angle thvc-qv4x4)xrj1jm, c me shock wave makes with the direction of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmospher)48 jh 9nu, ;4fmyul;apmtfmje of a planet where the speed of sound is only ab4mj f9m, u4 ;)mpln8afyh tuj;out 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling k ;osz3 mw47cfuk(g9u 8500 m/s strikes the ocean. Determine the shock wave angle it przc;f3u wmk(g 49 u7kosoduces
(a) in the air just before entering the ocean, $\approx$    (Round to the nearest integer)
(b) in the water just after entering.    $^{\circ} $
Assume T = 20 $^{\circ} $C

Show that the angle 6zo/(kskw f 1s$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a plane exac ne6nldu)tc,n4/ ko) qtly 1.5 km above the ground flying f4un6qc , k deot/n)l)naster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 12–34. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device that sends 20,q897 h-qlqu i2k21:jxjvha vw i* /wer000-Hz sound pulses downward from the bottom of the boat, an1q: 27hvjiu9wlwvq/ -xk 8jh aq*r e2id then detects echoes. If the maximum depth for which it is designed to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible range? x9c24d9h2wwb9dk qb7v x24cs yoey n 8$\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consistsqgm8j pib.zqcq ;- c/( of many plastic pipes of various lengths, which are open on both eng.iq mc pb8;-cj qq(z/ds.
(a) If the pipes have lengths of 3.0 m, 2.5 m, 2.0 m, 1.5 m and 1.0 m, what frequencies will be heard by a visitor’s ear placed near the ends of the pipes?
$f_{3.0}$ =    Hz
$f_{2.5}$ =    Hz
$f_{2.0}$ =    Hz
$f_{1.5}$ $\approx$    Hz (Round to the nearest integer)
$f_{1.0}$ $\approx$    Hz (Round to the nearest integer)
(b) Why does this display work better on a noisy day than on a quiet day?

  A single mosquito 5.0 m from a persodq7,e 0rddp7f ,qedz 4n makes a sound close to the threshold of human hearing (0 dB). What will be the sound level de47pqd,d z,0rfde 7q of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-dB srki mc qh;y21ozt/msi2p+ ./hound are heard simultip1qoy+tr m kc/2. zs/ih2m;haneously?    dB

  The sound level 12.0 m from a loudspeaker, placed fazbl;c9p ykji9)- :ubhx/ 9ain the open, is 105 dB. What is the acoustic pow9bcu k;hp -)j:9 9lxzai/yaf ber output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 m7l57dnu,fkkHz. The power output drops by 10 dB at 15 kHz. What is the power outpn, dmu5f7k7klut in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protec lrj 9-bn5is0si 0m:ov/ cdo-utive devices over their ears. Assume that the sound level of a jet airpl 0o/5-dn c siul-vj :i0r9mbosane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, thed3j)xpv+ qnvjc6(8xe bj 0 o:nfs 11tj gain, $\beta$ in decibels is defined as
$\beta$ = 10log($\frac{P_{out}}{P_{in}}$)
where $P_{in}$ is the power input to the system and $P_{out}$ is the power output. A particular stereo amplifier puts out 100 W of power for an input of 1 mW. What is its gain in dB?   dB

  Each string on a violin is tuned to a frequo+ evdu*.tp, oency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long between fixed points with a fj: l1ohwnge4tfz w 9/(undamental frequency of 440 Hz and a mass pj1l hgf4zwo9wn:e t(/er unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set intnat;c fb5;pd k rne(ax(r hza*4pk69:o vibration above a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when theeac9 p6:n4ap (h;b dk5;na(*kzxr rft distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of masst sb.ijw5f q;5 2.10 g is near a tube that is open at one end and also 75 cm long. How much tension should be in the string if it is to produce i 5. sbfjq;w5tresonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one full loopsi (bh(()t;kd0 ks cilv;mh-vy; e9sp ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000*3sr n3sl7, -sncp njhhtkbw gl 1*/d,-Hz range coming from two sources. The sound is loudest at points equidistant from the t3,/lhpnl k*r nn*17 s-hcd j,ssbg w3two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whumu)ymu 9ph3hwhe ,r-5*jrb 1m )hwr6 istles. One train is stationary. The conductor on the s1hrmry6 bw9 uhrew*jp m-h5u)3,um )htationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistlegel2x4qi./pkdk h2910qorhh, waxvl ) vt )5 l as it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. Howp wg .92xdr5e 1ikol qv0h)hxt4q)lv/a l2, hk fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed ofc/ p1k 82bt6e xye.njd cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the ./618eyxtbcn2jkd pe sound of a certain car drops by a full octave (frequency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, px:5snessq( 7u +l3lojroduce a beat frequency of 11 Hz. The shorts eoqsl:sl n+u(5jx37 er one is 2.40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of a railroad caf). 0( /i k n*,iefr8zrpvakvnr as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listens from the position A, in front of the car, (b) he is between the speakers, at B, and (cnpk (e.r vf8 iiz,r*0v/kf )na) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in the aorta is normally about 134;cz octb v2 -wnyxx0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waxzbcny-314; otw vx2c ves were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s while the mohvl(wqb) 8 r42f ;x4/g)+esy wshrfh fth is flying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is th)2 yq4 rwfhrl(4xg;+hwvbhsf) efs8 /e frequency of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency s3tekl2wl a;1 dound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away cael;t k3 a2ldw1n the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signals frxax 3c h:w 5polw,s7l 7ijq04eom one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundamental frequency of this horn, and which overtone is close to F sharp? (See Table 1x h50ipw,ql34sa 7j7x e clow:2–3.) Model as an open tube.

  Room acoustics for s 9te.yyzz:n q b5ap-5mtereo listening can be compromised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamental frequencies for -tpbe5zmayz .y:n 9q5the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, cally3l -c-hvznx, ed “singing rods,” involves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hav -l,xyc-hzn3 nd. With a little practice, the rod can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the threshold of hearing for theh 9 ob+k.iipv/ human ear at a frequency of aboutb.+p 9hvoki /i 1000 Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observerzoy w6, cxt 1zu91vv)e on the ground hears the sonic boom 1.5 min after the plane passes d ouv9,v1zw x)t1yec6zirectly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 15;xr.w lo8y hc3 $^{\circ} $ in a lake where the speed of the water wave is 2.2 km/h What is the speed of the boat?    km/h