What is the evidence that sound travels as a wavnc6an 538d zum*wcnh 9e?

What is the evidence that sound ia(a 8 xm v,bp jjw(u:c3g.kl.es9hq*ks a form of energy?

Children sometimes play with a homemade “te6hmpb9gm **( d+7rri klrg/lvlephone” by attaching a string to the bottoms of two paper cups. When the string is /*hr*67imp+rl vbk (d rmg lg9stretched 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 the other.

When a sound wave passes from air into water, do you expect the freqqkut4t kbhbm5xzng* kq-5aut3) 4i+-uency or wavelength to chanbk-n-3k tqubt )k44xh *+gaimt u55zqge?

What evidence can you give that the speed of sound in air does not q gqt/ ccn,35vdepend significantly on fre nqq5vt/ ,c3cgquency?

The voice of a person wh2r*4yo;5nffi* bo hbuo has inhaled helium sounds very high-pitched. Why?

How will the air temperature in ah0ob 1l4mjhaj k m-*q(2 neg(91tuaqf room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplit0+)qubqxoza 3 ude of sounds in various frequency ranges. (An exa uzoaq30x +b)qmple is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you m37 vtgyiu a0yr n2q/3zove up the vu/n3t yyi3 2zg0qra7 fingerboard toward the bridge?

A noisy truck approach*.;u)p xbiypz5dkm 2b k5+nhd es 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 of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction. km5y+5h2xkupb*n ;di bp.)d z]

Standing waves can be said tb .i(so -io.rozr)s 1bo be due to “interference in space,” whereas beats can be said to be due to “interference in ( 1obsbz-osr. .i)o irtime.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered,wn)8r) jpod** cmmj *u wzdx)62, admn would the points D and C (where destructivw* )uw2 ad nxdd,8*m)*6jmmpjo)nc rze and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who work in areas wi1 rpmy/hh- n-xth very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new tec p-xhy/nr1-hmhnology, 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 51uaiy 7yxg06+ t venqowp 8)ql3+gloa superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farthe5a03uo8lov nlw1 e pxq yq)ygg+6t+7ir apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if th*quy, x bd1k,3f7e+nse,tqu be source and observer move in the same direction, with the ,bk,t7ue1q3fy, q e* +udbxnssame velocity? Explain.

If a wind is blowing, will this alter the frek1wj )9.- adl,gxoo6i) ttt2cic vlx0quency of the sound heard by a person at rest with respect to the source? Is the wavelength v,ii).-1dt0owot c9x 2l6c)xk jgla tor velocity changed?

Figure 12–32 shows various positions of a cz uvv.u5px: p;hild in motion 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 fux vv 5up:p;.zor the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening ; xuyn5c+g a8jfor the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate;5y xa8njgcu+ the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his sh i18cv nv/3vt6wz0 ocuip just below 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 6vivc vz 1wn 3/ou0t8cat this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air al*ygsrzwmt) h-b oz73 3oa,d 2t 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, d4*na+lm j xuevi,o55kbb)l 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 backfire is heard (a) by thmu*ebjl nbav5i,,54d ) +kl xoe fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a clug u4:q2r,;zlg 7k xqmiff. The splash it makes when striking the water below is heard 3.5 s lag7 glrq,;u42 qx kmuz:ter. How high is the cliff?    m

  A person, with his ear to the groun:d (nm4v d kie48qk.mn ;.y.hm;pckp zd, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the a(m :qp mk. c.; 8n;p.yz 4ikevddkmhn4ir 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 madr;1n i *istzp)fr;p; le over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (atl;frpr)*ziis ;n1;p ) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain leve n+c;swgaiaqe7 qn4s,p xj v/rr15;u( l 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 intensvn 8wuq1k +-slity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a s9 iq wz; gbdh:o;e 9;k9cj;nwnound level of 95 dB when fired simultaneously at a certain place, what will be the soundd;; k9;cohz;qw9: ben9j wing level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distan n-bfajy8y2/z 5lbsp*b f; .ptce from an airplane with four equally noisy jet engines is experiencing 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 inte b8f nyb2l5at.s*-/;jz bpypfnsities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas fordnai b o*,n)mon:c:v 5 a CD playe:o,a) ncdvi5*nb:mn o r it is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output o8+1)sxx59 drquets g hbs3jc7f sound from a person speaking in normal conversation. Use Table 12–2. Assume th +tbh 8qs xs35xe7r1d)us cjg9e 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 strikes an eardrum whhf uz,m/ /ns3 oov/m/b*ltpzff 9/g-rose 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, while the more modest amplifier Bhxhpvw: br5/j jgletgzxb*41 pbm(4l2 ic0) ) is rated at 40 W. (a) Estimate the sound level in decibel*j5i(wbx41vz 2 txrhbbl0/ep :hpc4 g) j )lmgs 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 1306lowq 7qo; /ic 1r:dpp dB when placed 2.8 m in front of a loudspeaker 7qdco rlp16p wo:qi ;/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 +.k .sgpicft y0; lwjigl0 n92difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amountf+j0;kg.l0w 9yt.ci n2 pl igs? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tre :j+x :t hrrt(,prn(tipled, (a) by what factor will the intensity increase? Increase by a factor j rr ttx+pnh:r,e(t:(of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, butym3 vch 41nf *ag uyk;gi8ru51 one has twice the frequency of the other. Wm nu3yfak1 8gc451rygu ;ih v*hat is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that d ud)5am c1go2mw2 w(ucorresponds to a displacement amplitude of vibrating air)51odaww gmc2u(dm 2u molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seet-jv e-.i (-pln0 zourm as loud as a 100-Hz tone that has a 50-dB sound level? .or zpvt e0-( n-ulji-(See Fig. 12–6.)    dB

What are the lowest and highest frequencies tha )kvmklv ve.o3 up9jh),q0i;x0tq7 rs t an ear can detect when the sound level is 30 dBp09oi.)jel 0 ;3hqk,muk vs )vtqrx7v? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is the ( vchb:kvj0s-c8 b(tkki h)f5rg46fpg fl5)n ratio of highest to lowest intensib64v bc-kpfn0 5h c(g(ifj 8klshtk) vr5f)g: ty 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 frequency of 440 Hz. The length , u-gxt x i:ro2dl+rx8of the v xr+g2,xi: -rut8xlodibrating 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 an*t d e /j89xqvf.i5chsd first three audible overtones if the pipe.ctihqs 8 j/fd95e *xv 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 frequencth+6avl:w5hs a*pbz / y would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, ifph *wa6zbs 5h/a+vlt: 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 sb9itq 7ng3dc q qxcb)4zc2 -(hpanning the range of human hearing (20 Hz to 20 kHz), what would be the r72 (dcz -cbb q9igqh 4x3cqt)nange of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string (a,v4wpnjqb .jk5 k ,fhas a frequency of 540 Hz as its third harmonic. What will be its fundamental frequency i,k a b,vwk45pqfj(jn. f 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 tune(t9 ish / bfah6-ay42ujvtio 8d to play E above middle C (330 Hz)( s8vyht2ajtob/-46f hii a9u.
(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 xbtv- c(gq 4m*ynqt), emits middle C (262 Hz) when the temq,txq-m(v)b ty g*n4cperature 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 4/psv9e 2 wy jdvht*6yat 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece f/fli/v,wi(h;z +dsrof the flute in Example 12–10 should the hole be that must be uncovered to play D above middle C at 294i /dw+l;zv s(/ffihr, 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 cavvk 1ci59;d /f5kxu p0c(qnhvn resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in betc/idc(;kn05 u 9 xvv5fp 1kqvhween. (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 ismr4 a2lx +z 0 mxuo.ouog3e,)z open at both ends. It resonates at two successive harmonics of frequencies 275rex.zl oz+a0) xu2 ogm o4u,3m 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 m gqy24.;*fa nf2v6m s qs6 v;j:idstn$^{\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 withi); tjz;4 c4zbwyrk5mdn the audible range for a 2.14-m-long organ pipe atm)5tkd;c zb 4r4; jyzw 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 the out4 rk+e2gh(cqmc,b oddb (7l7h u gnb*2side and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of your answer to the information in the graph of Fg,l77ck( n(2ddbrm*o bu+eh4 2hgbcqig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when t0 zq*dvo wdfgnj, 52 ixu(a0n:rying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency 5gvanfj2u w0d xz(n,qd i0*o:is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz9gk g9w h0:zjqovd 68k.mz,hb) 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 23.5 kHz, while another 0xe-0 g9czuzh 0ktij9 (brand X) operates at an 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 fet 0c9 9h0juizxgz-k0 requency of brand X.    kHz

  A guitar string produces 4 beo ckkzmj4( 2;me-g(co4c/jqqats/s when sounded with a 350-Hz tuning fork and 9 bc4q/ cqcmoe(kk o4g;mjz(j 2 -eats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to5 yjmmlf6l 7*-xi) bxfr/rr5 d the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are rxlf/ir yxmrf 6)b-j57 5*mld played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to 5yn3t7gx z vr8bbi82wplay middle C (262 Hz), but one is at 5.0°C 532 n8bgi8xzvrwy7 bt and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Hz; w:/ ifi a v4y/pymyhg+) (qz)urhen 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. What are ifhm/ :rzvpia)yy/u +4yg()qthe 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 arekvqwks ++-o ;w 1.80 m apart. A person stands 3.00 m from one speaker and 3.50 m from the k;q+ swvo k+w-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 bel moubo;wz d wjj6*671 vibrating at 132 Hz, but a piano tuner hears three j6zm7 oww*oj;6 1ulbdbeats 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 n 9xdwsdw) ,0b+a*lz band 2.76 m in air. How many beats per second will be heard? (Assume T l)0z*bxwd+ bsad9w ,n = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequenc j k ujnp(ww.:0+qul2ey of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30k: .q(ju0l e2uj+wpwn m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do yoq(*)iwnuxkn, j7 )1txw0msma g o4iy7u detect if a fire engine whose siren emits at 1550 Hz moves at a speed of 32 m/)7i)j(7,* uaos tgx0 m 1qi ywmnxkwn4s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving toed a88p2dq0e: xtgl0 fward you at 15 m/s versus you moving toward it at 15 m/s Are 8:gt2fp 0e0lxa d eq8dthe 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 mz8/ pom,mz8 x4ysn5 jyq58gosingle frequency horn. When one is at rest and the other is moving toward the first at 15 m/s theyojmyzp o5nq8 / ,gz45mx88ms driver 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 ultrasonic sound wav(0*u4c znp2m k:tuyx jqjey) /es at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the received soun(ezjn xk yu0 q:mjy2pu4t/c *)d frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies,mg rfsf/mj 9do959jn)x7c 3 d;orsn* j the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency doe3r fj9s7n/ xfoo m9n5jjg )s*;m9ddcrs the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba wb j*aeyi41 i3*jlkkd)t d; zu/as 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 thuai)dk lij b* d;ytz/kj* e314e 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 usez*y ox/o;3iom s ultrasound waves to measure blood-flow speeds. Suppose the doy*o3omx zi/;evice 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 the sound source?   Hz

  The Doppler effect using ultrasonic waves of frequen*hpta 0g eo5gf* 8s( 2oks0bzfcy $2.25 \times10^{ 6}$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 ffep -s)ru-e w-requency 570 Hz. When the wind velocity is 12 m/s frorsw-)-fpu -e em the north, 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 lan v; rwxvil7;q0d if its speed 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 Magef*g3 qfaw/ 6ch 2.3 where the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the dir /f3w6*e ggafqection 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 atmosphere of a 9;ia)vuk5u+ iqb.n; gras3c rplanet where the speed of sound is onqasu aukr) r+g;v9n i;b53i.cly about 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 -q. (k8fgsrwr r5nu.s ,fmyk0strikes the ocean. Determine the shock wave angle rr kws,nfs mg0.fy8-5rqk (u .it produces
(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 5 z81fooli/; yo7 c8ybklno 3a$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overh7tc.jne71g7g 4,a(qdyvy o bp ead and see a plane exactly 1.5 km above the ground flying faster than the speed of sound. By the time you hear the sonic bong4.ejoay1cp(q td7vg b 77,yom, 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 th.s w cr z3v6f4xtj;2pjat sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for whichzj6v rtc2;4.3pjwf sx it is designed to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octavergo3u+;le88c 4t -tycvz7 qc ts are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe sy9uy95 v4w0fllruwx/a , y(zepmphony. It consists of many plastic pipes of various lengths, which are open o wp zu0luyv59xa/lw4f, (ry9e n 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 m pk d t9lb6yuk 3 b,x)nfz15fv-from a person makes a sound close to the threshold of human hearin bkld3 bkf9n ) fu51-xtv6,zpyg (0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an:xg-8tr *+5bo tpx ezob/ nwtz3y v95z 87-dB sound are heard simultaneously9txg bzr*+oxy5t p-wnt/ 3o8 v5ze :zb?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 aw 0;u kak.yd(iz6(wpo 7s:, r tc:liudB. What is the acoustic power ou,dkp(.cat;iak6 s wyo:w :r z( li7u0utput (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated atl6lx+y pf ne/9vu;6jb)lwo4 p0jx5 rv 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is)x;w 5vl j6bjn94epv +/l fyr0o6xlpu the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear7tyw(w :) uqq zxo3fgve4i 9/r protective devices over their ears. Assume that the sound level of a jet airplane 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 gti4fr)/9eyq3v ouqw 7 (:zwx distance of 30 m from a jet airplane engine?    W

  In audio and communications system.*ydh e3ke6i dfy(0m .wajc -is, 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 i j jmzmdpereey.q 9;gt65r 968s tuned to a frequency 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 fundamenta 3 jht/i3qugs0lh2xt66y6 swpl frequency of 440 Hz and atltx3y6q s 2p w j0h3hugs6i6/ 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 vis(oe g2(6qgnlbration 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 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 g(nego lq( 62sfork?   Hz

  A 75-cm-long guitar string of mass 2.10 g is near a tube that is open akbu-jl.kpc tu(n /mq9+6v (oat one end and also 75 cm long. How much tension shou/ol(+t. puvk(na-bumc69j k qld be in the string if it is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed 0) e)wzn12n w;oqcrczto resonate 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 50kz s,czzk/z;igf;lyqwb)1) +f bx: 7s 0–1000-Hz range coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is mcwzs/q17:+sbkly k,);gz zf) fz ;bxiinimal 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 is statis( +nwa 6;oddbonary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of the m wn 6oba+;s(ddoving train?   m/s

  The frequency of a steam train whisigl(zoko.b0 t-+cz02r c3xom tle as it approaches you is 538 Hz. After it passes you, io-c+t3 rcl 0z2om(iogbzx.0k ts frequency is measured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars just by listening to the-wmf 8.mu gfx* difference in pitch of the engine noise between approaching and receding ugfxmfwm.*8- cars. Suppose the 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 togetherud;zg +9vri. f, produce a beat frequency of 11 Hz. The shorter one is f9.z+ ;iru gdv2.40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of a r) -onzptx.o2+do;db oailroad car as it moves past a stationary observer at 10 m/s as shown z.bx p)doo+o t2d-o;n 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 (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flo j u8ncfp 977,3omjpxse*h fk8w in the aorta is normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? Assuoxnjp9 pu3mke fcj f8,h8 s*77me that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth a p 3z; :f/t(frf m;*wrcbat.yrb5:gqd t speed 6.5 m/s while the moth is flying toward the ba:gb.:tpf*;zb(cr ;ff qr3rd/ yw t5amt at speed 5 m/s The bat emits 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 seriesvswq4hf, l d-/ of high frequency sound 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 can the moth be detected by the bat slv4hqsw/- ,fdo that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 1 m*p)u;4: 7vu kdhgmkk2–38) was once used to send signals from 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 Tapdvkm:kg*) 7muh;uk 4ble 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be comprome3g( k,ri6c dcised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the 6d,ecrgcki(3 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 standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, slender +xe+ha b i nzgg8m0*-ealuminum rod held in the hand near the rod’s midpoint. The rod is strokegix -nza+m*0ge b +h8ed with the other hand. 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 hearbgd5 jov5+ev (ing for the human ear at a frequency of about 1000 Hz is d5o5 b+v j(vge$I_0$ = $1 \times10^{12 } W / m^2$ 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 observer on the 7gl bl9(0k dqmw9/uhg ground hears the sonic boom 1.5 min after the plane pas(wlbhg/ 0 k 9udl9mg7qses directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedbole-s r b75hjm1at is 15 $^{\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