What is the evidence tha y+0t/d7gkiqh.r d3 zmv88xdft sound travels as a wave?

What is the evidence that sound is av,h zd fgx70jsz-) v7p form of energy?

Children sometimes play with a homemade “tjs0/.dmyj f js;7eg7felephone” 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 how the sound wave travels from one cup to thee m 7 /yf.jg0jsf7dj;s other.

When a sound wave passes from air into water, do you expect the frequency or wavh-yg6 :cq8s pqelength to change? phy:qs6c-8 qg

What evidence can you give that the speed of sound in air dh:nzc4u6udra, m3ab- oes not depend significantlru amn3ca,u :4b d6-hzy on frequency?

The voice of a person wh-zu k,m7umzbbua or0(b9) 4tko has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affec0ql-9xkegq qi,1a 5id t the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude of .zgz hn qha-:5hiz:z4sounds in various hgnh z:-aqh z:4 .5zizfrequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you move uw 6fu:0ld k8jb dmxw8z16 em,tp the fingerboard toward the bridge? w,6lbxd:8jf mt 1uzmk 80dw e6

A noisy truck approaches you from behind a buildis6v3me) n l5bkng. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of t e ms5b3ln6v)khe high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whereas beats rwpr +6kw8q4nikh-y+can be said to be due to “interference in tirrk+ n6ykp4- 8hqww+ime.” Explain.

In Fig. 12–16, if the frequency of the epph1q0*hf 4zspeakers were lowered, would the points D and C (where destructive and constref* h0zp h4q1puctive interference occur) move farther apart or closer together?

Traditional methods of protectin x) ;doq k.1jgncpp q5s8z/*qdg the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverjq /d.xpcosq*85pn kzg)q;1 dts 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 Fitlf/ l iohktw55tm2 xm/6d. fmc6k/5vg. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in kxt5h56dim2m lo5fm6f/vt t.kwl/ c/Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observs(catlhann,p 7, 6yo (er move in the same direction, wit(6ohp,nnt(yscla, 7 ah the same velocity? Explain.

If a wind is blowing, will t.elv2l pq/ t;bwnqg *,his alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavn/tw l* gq,elbp.q; v2elength or velocity changed?

Figure 12–32 shows various positions of a child in motio1jymn0 a r)f7wnr -a-mn on a swing. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reaso wmm 0nfr-r)-y7jan1aning.

  A hiker determines t nham2e7qv ;i )tk1s/.s4ymvr he length of a lake by listening for the echo of her shout reflecteea7r4hmvvkmq /t s )2.;n1siy d by a cliff at the far end of the lake. She hears 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 below the f v)at puu5e(;p s1*vwwaterline. 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 seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.vu(wes5t p) ;uvp1 fa*    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in airi(nm n7zfv9 w2 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 above a school of tuna on a foz)w29 oowebp1 ggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapseww1)9 p2oe bzos before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The s+oefnsm4j q *9l,z qx:plash it makes when striking the water below is heard 3.5 s lqlf qxm sznj9:4+eo,* ater. How high is the cliff?    m

  A person, with his ear to the bro1 /v,lvvb- cyp-0p+re*kqground, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.qcvkpo rb +l-1,erpv0* -bv/y1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “* dsovq,oh4 1xph;m-x5-second rule” for estimating the distance fos,4 xpx*1q-o;mvhd h rom a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain /7vher rbv;z.fgue5p1 z 3sc0vn.aa(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 sgu ta+tg 1s*)fe+o v j+zl3;m0vdj2p sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a soun,k/nnn7le i 6i1 t,ejxsjzf4+d level of 95 dB when fired simultaneously at a certain7ix4i 1e+/, sltzj jenk,6nn f place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airpla/o-z l *-cikc6zx(bte 2bau3kne with four equally noisy jet engines is expelocu-i*e zb-z2(kbct63 ax/k riencing a sound level bordering on pain, 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 )0w)n qm9eppz p .-aqzbcja //y4u- 1*jlbhemhave a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the/y c man0mp q-bph ) jwa.)91*z4q p-zjue/leb signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound frcl82)h3s jj8bgfp jt,1m-to o om a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered ocj2-1o b j8l8mgh pfs, 3jt)otn 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 s06y ryg0*jndctrikes 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 rated at 250 W, qszr9guq; en3gfn 0d143p nr3while the more modest amplifier B is rated at 40 W. (a) Estimate3r;ps ng qn1 u 4ezgrfq9d033n the sound level 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 dB meter registered 130 dB when7iqm(.ewm 4ds placed 2.8 m in front of a loudspeaker on ti(4ew7 . mqdmshe 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 s/0v- *z+p 3edd zzq8k x)bupfzound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: zzb-fqvx3)u ddz ek/pp*+ 0z8 See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what76e v+cr zjv(j factor will the intensity increase? Increas(vcj7j6+v ezre by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twice the frequepa14(as cb3 mtncy of the other. What is the ra 3pt1ba4ms(catio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air th0e -hrxo0ne-evst94xat corresponds to a displacement amplitude of vibra -ex x4rt9hve n-os0e0ting air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz toi:s-x -h)jrur ne that has a 50-dB sound level? (See Fig. 12rs:rh) --uixj–6.)    dB

What are the lowest and highest frequencies that xwz0 .:js7 uwpan ear can detect when the sound level i: .xspjw7 uwz0s 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of s/+qjcb wiq(y-* wnyow po ;9/aound levels. What is the ratio of highest to lown(;jwc*/9+poqw a oq by -wi/yest 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 a fundamental frequen7 2jg qtv0iozu)a4bm,cy of 440 Hz. The length of the vit) ,jqug74ibmv 0oza2brating portion is 32 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 long. What are the fundamental aym vhmztcm-r4;7w)3f nd first three audible owmzrcf v7m3-4;)ym htvertones if the pipe 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 would you expect from blowing across the top of an5*:). xy kw+q jkbpq)vho6cm3h ms5je empty soda bottle that is 18 cm deep, if you assumed it was a closed sb5k)mq kojmc3* jp:h+y65 vwq h .e)xtube?    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-ty/ y,;ut5yhs mu1p,m qube pipes spanning the range of human hearing (20 Hz to 20 kHzqmu5upmy 1,t; y,hs/y), 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 frz, 2h7z3t5id 5w nxwtjequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a lengthjhwt z75it5n, xw3d2z of only 60% of its original length?   Hz

  An unfingered guitar string icns2; jy,-hjeg9f)cp z1 djxm2km* k 3s 0.73 m long and is tuned to play E above middle C (330 Hz)h 1,; -ypnkxj2 mfc2k3c*d )j9ezg smj.
(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 organ pipe that emits miiew7iu: zr4dy*n( +f mddle C (262 Hz) when the temperature is 2fw47yi+ue*znidm (:r 1 $^{\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 r3hx j+ o;l:x( 1cjz xygwb:(u20 $^{\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 1- kl 0emc:xxdm tzh+0ay0uq38 ku1wjbe that must be unc1x0kd31k+ujcxtye z 0wal muh8 -: q0movered to play D above middle C at 294 Hz?    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 264 Hz, 440caoe :rgby y+f15m /a+ Hz, and 616 Hz, but not at any other frequencies in between. (a) Show w gmyaa++ bf:/o5r1yechy 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 both l(n d,fa*an rqy vk;6)ends. It resonates at two successive harmonics of frequencies 275 Hz and 330 Hz. What isln,q d*ykfn)var6a(;
(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 c y;c7rufeh+07g r9ja$^{\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 present within the audible range for a 5cb) 6auhp. oi d7up:b2.14-m-long organ pi .dhu5b7p u)c 6oi:pabpe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2 cj 4:k+.a:ygkbl.cj k.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in tal4kc . .:c:kj+j kbyghe 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 one beat everbb-,j wtbh6z8y 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the 6,wbzb hjt8-bother string? ±    Hz

  What is the beat frequency if m04 4ejj k a6cop6pio jmftl:72iddle 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 operates at 2 .3trbt hr3jsfa( ,r-m3.5 kHz, while another (brand X) operates at an unknown frequency. If neither whh,rjrrf.mtst 3- ( 3baistle 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 a 350-Hz tuning fork ag8 .(q7 hmc,*c tg2bv3 ujv2v sdm5vzlnd 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibratigcj7vm*h. dmzs vlv2 gu2 qt3, (cv8b5onal frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension i *54ol5woud; os c3y2o7vbwgb8 cmkx8n one string is then decreased by 2.0%. What will be the beat freqy losgx o8b o4v;wodbc um7253wc* k85uency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be he+lsc,rjt;n :pard if two identical flutes each try to play middle C (262 Hz), but onetrnp js,;:c+l is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forksm 6oan,fs6b3bp; j* pz y*xulk*/i8pb, 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 Cbpj6o*kmp b y*x6*s,ni3f/uz pl a;b8 are sounded together, the beat frequency is 4 Hz. What 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 person stands 3.00q1fw5ae4/ w kc m from one speaker and 3.50 m from the4wc k51 fw/eqa 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 vibrating at 132 Hz, but a piano tunerus*ygs +aojq /s4 fz(: hear:+gf4ss *szq oyua/j(s three beats every 2.0 s when they are played 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 wavelengths 2.64 m and 2.76 m 7l/qec 778;xuktg pejin air. How many beats per seconcp jtk8; 7xq/ 77gleued will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz when at rewag9h5 na 09s5 (thpbist. What frequency do you detect if you move with a speed o paah(t5gs n b99hw0i5f 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a fire engine w- )ubqvuhzn.0hose siren emits at 1550 Hz moves at a u0qn hb.vuz-)speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in freq17ae(wg( ca ,ekykx h:uency if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 7g e,1cw(hk ay:xka(em/s Are the two frequencies exactly the same? Are 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 single hg8 +gjziyk:h88c;ioa k0r1h frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. Wk8y;h0gjh1+gc i:h 8r ak8ziohat is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends outvf-rnm3 rli:j is f1o0q,/ff; ultrasonic sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s;-m f/3f loirvq is1:jr ,0ffn What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it qkq*3;5 porl+e8mz lic5jja 4 flies, the bat emits an ultrasonic sound wave wi+;e5paqilqmj *rok jc l4z83 5th frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving flats n2k7(hrjhk( train car at a frequency of 75 Hz, and a second identical tuba played the same tone whiles n hk(j27(hrk at rest in the railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeds zkirvk-)-tcpcu0f2kb5( / p /2 i1.wabmiwmv. Suppose the device emits sound at 3.5 MHz,cia 21 k ipwzk/-)ckm/w 50fvbum(pi 2.b-rvt 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 the sound source?   Hz

  The Doppler effect using 86:krvi97 sofvppwr 8, hr anbq*.sy- ultrasonic waves 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 frequendh//f4ye.cmt cy 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are located,ehf.t /dyc/4m 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 speedgo 9 y69+lrajq 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 Mach 2.3 b+ q.shmu :qv+us98pkwhere the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of tspb8 hsq.+vkm:q + u9uhe 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 atmosphere of a peracih s-( f00:**uvu3 mseralanet where the speed of sound is only abo3-uf a* crue(e: msv00*shriaut 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 8500 m/s strikes the oceanr-v6l5sccx-r ffl4 q:1ms 9tq. Determine the shock wave angle it produces csmt5-4xvs-6qrrc lq9: ff l1
(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 e4 4gkaghv/i( $/theta$ 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 exactly 1.5 kmb3x 6sxf:l gl7 above the ground flying faster 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. 3 f6l7x:glsxb12–34. 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 devick k ol9fqnjpa59*8 c: ++gxa .o3mhbuoe that sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 200 m, what is thob+l9.aou *n+:98mj3 o fhq5 cpkgak xe minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible lrxp6 ;w0lflx6v6 7gnrange? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. I.p x:r3lw a:*qdg udy1t consists of many plastic pipes of variousd :1ya.d:wuqlrgx3 *p lengths, which are open on both ends.
(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 m7w g :nr;eadv9- qp z(db9lr4a from a person makes a sound close to the threshold of human hearing (0 dB). What will be the sound level of 1000 such mosquitoes? 9 q7r9e4lpn gr(w da:a;bzvd-    dB

  What is the resultant sound level when an 82-dB sound and an 87-dB sound+p/ /qwtg m8g+x*ugsy c0 5gn7vksjb : are heard simult /pg 8n7gqsbjvkmgxy t +*sgw :0u5+/caneously?    dB

  The sound level 12.0 m fr +z.a6do k+gliom a loudspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the speaker, assuming it gz +ik a6+d.olradiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The po *u1dxuh.t ct,wer output drops by 10 dB at 15 kHz. What is the power output* x1tu,u tdh.c in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protectiviax o+c,z)upz jz.s/)e devices over their ears. Assume that the sound level of a jet airplane engine, at a dist z,+)p/ciau) o z.jxzsance 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 communication 2/q xnvd:eos/3lb *kq 61aa4a j1mtsds systems, the 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 e v-vqd-x2 /j9.du fazfrequency 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 3ts7do i4 xnj2dy3b)dbetween fixed points with a fundamental frb247yxt)3o sid d jn3dequency of 440 Hz and a mass per 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 into vibration above a vertical opeozyf(jkz *xt- ) .juwhd:.t4 hbe8z(f n 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 theht wthf e).x(k 4juojz.:d b(yz-*f8 z tuning fork when the 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 mass 2.10 g is near a tux 1qos)zur a3(be that is open at one end and also 75 cm long. How much tension should be in the string if it)s (u axo1r3qz is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to reso2(w)keceu3a ; m ynj53a nes-7*upsopnate as one full loop ($\frac{1}{2}\lambda$) 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-Hz range coming fromvi92xaj3z atia .p/;xmiec-2 two sources. The sound is loudest at points equidistant from the two source.eciv ; jzp392imaxt x-2a/ ias. 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 whistles. One train fh.9/s lsz* ebrnf/zn 3j9-diis stationary. The conductor on the station.db-ihsj//r3 e9 lff nz9z*nsary 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 whistle as it approaches you is 538 ph*.*+foveaq//4hw,gjeyce Hz. After it passes you, its frequency is meoe,pc.+hq/ ag/jew hey 4*v*f asured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can esjhvr9n9 8s3r ctimate the speed of cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by3r9 s9c nh8jrv on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat fr 7 fcsieb)ah1ul/v6)w equency of 11 Hz. The shorter one is 2.40 6uh)w 7/ a 1sb)cilfvem long. How long is the other?    m

Two loudspeakers are at opposite ends of a ras );i.oe:+:pps-uqb xpw(y*z3i bj ak z50qqpilroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound freq.ppusjxqek a3i*p0yb)zq:b (;w o:-5is qp z+uencies 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 (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in the aorta iso*+q v* u yuxx4.n:o dqawf(k/ normally about 0.32 m/s what beat frequency would you expect if 5.5*au+(f wkyx u q.dqx/oov 4*n:0-MHz ultrasound waves 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 speed4(-to1 iw u:zljpn4tv 6.5 m/s while the moth is flying toward the bat at speed 5 m/s The bat em(lvjz 41u:n-t 4 ptoiwits a sound wave of 51.35 kHz. What is the frequency of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound pulses as it approaches a m1jnc2/o lio5prx l06k oth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected0nipo5lx /jo 16 lckr2 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 from one Alpine;ah 4*uhi g7ixng3. sb(erca9 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 freiunriahhx;.sc4g *7ab (g 9e3quency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be cxdf3fag7xp s +)r h4u2ompromised 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 the standingf3fug 2 x7)a+h prs4xd waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, slender alums u9n:ay0 mip:inum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, loud, 0yimup:: na9sringing 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 the human ear at a fr2w8mdyc5 b 6oiequency of about 6c2ib5o 8w dmy1000 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 2.0k-dls54i qcbd l:4g h h8ss3d6. An observer on the ground hears the sonic boom 1.5 min after the plane passes dhgdc8d s34 654sh lqs-db:lk iirectly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 15x90l toe;umu vx*6f2u $^{\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