What is the evidence that soundgbaq7/ p4 km n -a upmuxa.+)xmf4.i6z travels as a wave?

What is the evidence that soun )*g;d rtq1 bzocl 1vd59i9ms.99fsf-jk xoxld is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a stringl2g f)(;rs04 jbz djhpp4s: wk 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 rgjsz fs0 42k: wdbph4l;)pj(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 in, 0lktaw4ov:imy7 ) uhto water, do you expect the frequency or wavelength to chaiuwakv mo:7 ,)y4 lt0hnge?

What evidence can you rfeart 08g9fyn63 z0,b. nqzmibj.+d give that the speed of sound in air does not depend significantm.qf ,nr ny00 abgrbiz+ 6.ed9j tzf83ly on frequency?

The voice of a person who has inhaled helium sounds very xg5+x5btrpt(9 7npjy high-pitched. Why?

How will the air temperature in a room affect the pitch of 79z fecrvnahx/ 7gr)(organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude of soun07-3jjh0hslwqd)+ra ub r 9aeds in various frequency 9u)+d lw hb0-a rjh3sejar70qranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer togtkyhx 0+1q k)mym7cc -ether as you move up tm)-kk mc0h 7q1y+tycxhe fingerboard toward the bridge?

A noisy truck approaches you from behind a building. Ioiva;i z;ds4n :0 lf4lnitially 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. nz 4f; v40ialls;di:oExplain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference5 rj..+kae ij8p4vndrg+/e.sj1aet l in space,” whereas beats can be said to be due to “interference in time.” i4.pas vajd1/t5+rg e+n.er8l ejk.j Explain.

In Fig. 12–16, if the frequency o/fl x36mtktt. f the speakers were lowered, would the points D and C (whe6 tt3tlmfkx/.re destructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protect(/xco yg.b;g6ok8gbgx bol( -8c 5fswing the hearing of people who work in areas with very high noise levels have ckfoy gb8cg6(5cg/g 8obb .l -(ows ;xxonsisted 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, 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. 12ut2s/r)w +0mwghbrs o+ly . *o–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), arerms uso.wr *2 +byl)to/h g0w+ the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move z8fxy d2)bwq v1p hq/+in the same direction, with the same velocity?)/pbf2 8 dzxh qwqv1y+ Explain.

If a wind is blowing, will this alter the frequency of the sound heard :f 4. cmb5vw w x-;cch46znebdby a person at rest with respect to the so4ef .cbz5v:w 4 cbx 6-mhw;ndcurce? Is the wavelength or velocity changed?

Figure 12–32 shows variousvaq1 *176m/mh zild -ql ;;ssne pyf.d positions of a child 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 emqv i6 1dlzsm fq .lh;a/7*ps1ynd; -frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a ljq ycs*zsx;- /ake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after s;-q /xc*sz jsyhouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He hears the (,h uae7 thcn:echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is thh ahec(:n7ut ,e 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.    $ \times10^{ 3}$m

  (a) Calculate the wavelef.hjs mye8/;9 rl s)krngths in air 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 abod.t c4zz ry.zmj9mla)(qp / w4 /qmon/ve a school of tuna on a foggy day. Without warning, an engine backfire occurs on a.cmz m wm( zz4or/qjnl/.pd t49a/ yq)nother boat 1.0 km away (Fig. 12–33). How much time elapses 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 splash it makes when strikingr0 g893jto g4myoyv* m the water below is heard 3.5 s later. How rgy g3ovt0m8j4mo y9*high is the cliff?    m

  A person, with his ear to the ground, sees a huge stkj0*v+oh d8m*yf+dy 1npwr n -one 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 1.1 s apart. Hj*nymr++dfv-nd *kw0hpoy 1 8ow far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distancadv*s+jw y (./iy jv;)-sciwie by the “5-second rule” for estimating the distance from a lightning )i-awiy.iv vj( /wyscsj +d ;*strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at t//eyii ipi6j 1he 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 leve:f *.3qphkrjk l of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB5hka z,6lc+ l2fplp n 3r.cvo2 when fired simultaneously at a certain place, what will be the soundvo6.lfzn c3l2k,+a p52l chpr level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with fotfpr 11,z,fcmur 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 dow,,c 1 1ftfzpmrn all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have ajt. he jl,d7*n).srhcuse2 s tv3i-,j signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensitie*. ,tnjdjl73s h-v hr eiut.se),s cj2s 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 speakr6o,4 tk4te eging in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere goe t4erk,4 t6centered 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 wrw0/dsyx,9( kitvq- zhose 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 m. x vb7 o hs-788wo5vzgcuc*er .pngx1odest amplifier B is rated at 40 W. (a) Estimate the sound 7 cr-8xo8vuhzn *vxbc o.5egs p. 7g1wlevel 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 when placed 2.8 m iw x3a /bb)bw),:vpn3glu b-ju,m,yw in front of a loudspeaker on thep yli:-b w)wuw3 mvb)jxau/3b,,b ,ng 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 dls4wj(h *x2k2gn (cgypl9ph ;etect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ b(cwpj *94phnsl g;k2g2 x hl(yy this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled,mq.g ;cytqpuos ;/v +;xgg 1)q (a) by what factor will the intensity increase? Increase by gc q;y m vp+qs/o)tg;gq ux;.1a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displaceme 7ek4eac95 ijdnt amplitudes, but one has twice the frequency of the other. What is the ratio of their intensities? ek9dj4ce a7i5  

  What would be the sound level (in dB) of1d rtu o6s*(wb a sound wave in air that corresponds to a displacement amplitude of vibrating air m b6w*dtso (u1rolecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to-.kmd :d au,t1sqh:smlat0 (g seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig.skdmdma. su, -h0 (g:t:a 1tql 12–6.)    dB

What are the lowest and highest frequencies that an ear (v0xwtfb* c f2can detect when the sound level is 30 dcwf2 x(fbt0v*B? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is tc-4scs q0tu6waprbxk) q) k2:he ratio of highest to lowest intensity at s -kpwq:akb 6u24sc))cr0qxt
(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 44n4d gvr7+1ypbr9 0yp rn39vr:w z dh;2yf x9kn0 Hz. The length of the vibrating portion is 32 c09 ;3 yhkypxrnzr79p rv1gd:nfrv 9 yb4n 2+wdm, 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 fundamer)ncd/utz 6vh, /( imental and first three audible overtones ,/z r(/cmdhiv n6eut) 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 wou 3z0n/uquyi /dbo:ej 3ld you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was :/endbj03q i oyu3 uz/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-y n2 ghuv:mqdemy h04d+0j;gc 1+t0d m3wf0mdtube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes required? dumyv; dd dmmt1 0q3m2jf+0 cgn:4yh0weh g0+$L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency ofw yzffyzh:9l,3p08 g y0cdj3p 540 Hz as its third harmonic. What will be its fun3p08yg l3 f ,dcw9yzz :jfyhp0damental frequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string i lwamv*u-n 7ygr-( br6c,w2q cs 0.73 m long and is tuned to play E above middle C (330 Hz). ,m lrng*-v y(c-urbawqw67 2c
(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 o9z,bm/: 1fd d/b w r +zr+3c(6vdviqb8mzouwsrgan pipe that emits middle C (262 Hz) when the temperature dmqi8c:13v bo9b rdu +mw+sb,vz6rzzd/f (w/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 20loa iqj.x;5,xhkr 0vete3h01+se ;hb $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in ce229 kkk/n:*5 q u pue/loylvp6up i.Example 12–10 should the hole be that must be unpnk i/u/:69e5ol2 plc qupeku*vy .2kcovered 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 pipvzo1u8e lr9+3b 4mg2j nrhyb(e can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between.2zr nl93ye hbg m 4v1rob+(ju8 (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 both ends. a)/us g (ht6if-4fmo1w i2qgx+w 8asaIt resonates at two successive ha is-w 2xiqghwaf/a(ugt4o1 m6+ )asf 8rmonics of frequencies 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 lpgs:)v8 dp;jm9fx ) x$^{\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 6: bn w6i+rg *sjwooz2present within the audible range for a 2.14-m-long organ pipe ato : 26zwb6i*rjgown s+ 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 out3 qzse7kubo87y dhm*c.s7tp1m/is m6side 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. 176is7ms bh emy o*8kdqm3c zus 7/.tpWhat 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 every 2.0 s when trying to adjust two strqvbg*pf;+1qym gy94 rings, one of which is sounding 440 Hz. How far off in frequv +y mqr; *fgpgq491byency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz) ancom*c i/8d- jwd $C^＃$ (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 0qf0fv9( rs6pj hwt+ k23.5 kHz, while another (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 opsfkrv9 0hqf (+60 wpjterating frequency of brand X.    kHz

  A guitar string produces 4 beatsv)xlc 7 mvbpb3/spw /z( z8v+)hkvhr3/s when sounded with a 350-Hz tuning fork and 9 be8blpv/vv)pxw z)/r+s(v 3 hk3 7 zbhmcats/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 to the same frequency, 294 Hz. T2lm gvga8mpb*5ip *+:r;cpa w8q pd,ohe tension 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,* icpa5w;8rvd8q *pm+p2l m:gpaogb Eq. 11–13.]    Hz

  How many beats will be heard if two identiclkifonbf)5il+zjhd6 0(--h .q) x p yeal flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other at 25.0 (i5eo -6-jfdfkl.b y+))lz phih 0nxq $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has/k yfp ,gwg;geh(v/u5 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, y(u fv; /gkh5gpg e,/wthe 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 3.0q++uy7rm.le . p ou/qw0 m from one speaker and 3.50 m from the other..7oeq +mr+u/qwl.up y
(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 2/j7.sajxbdld +sa8wHz, but a piano tuner hears three beats every 2.0 s when they ar./sw28 dj db s7+axjlae 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 in air. How many beats peria-juy b:)j(tjt iy.: second will be heard? y.t) :i :u-(ia yjjbjt(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.d,si-(05 qbzjnk ck+ho/fvn 0 ca0dd at rest. What v0cd(hj0o kd cs in/b,kz n50f+d-.aqfrequency do you detect if you move 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 detect if a tfgs4k2h/ re1fire engine whose siren emits at 1550 Hz moves akt g/fs2ehr41t a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz pe4 b6a6i4tuu source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the 6ue6ibpu4 a4ttwo 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 frequency hornyl*m97uy/qx y) kg0yn. When one is at rest and the other is moving toward the fir7y/kmu9*n lqyy0yg )xst at 15 m/s the 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 ultrasong .hzp0lmfqs1ui7t 3vk t6 /xp;m0f*zic 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 received soundk7fi sf6muh g tv; pzqpzt/* 1x00.3ml frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, thn8fs+oap/p5ny * bl r,e bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequsn p+p8alno* 5,rfby/ency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler ec42 nb-t w9oocxperiments, 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.bcwt-o29 4c no 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-( ovlkn2 eq4q)flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue ( q2ov)4lkn qeis 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 wavetuwj): :yd+u6 7w zhkzs 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 veloci9:pac ojzeryg*:4x. wty is 12 m/s from the north, what f:o*gerj:xaw9 yz 4.c prequency 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 lando+,q x, ljccc5 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 Mache boyt-2yy9- z 2.3 where the speed of sound is 310 m/s (a) What is the angle the shock wave makes wit2 b- -z9yyyoeth 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 atmosphef 4wadi:n8sa1kl2h )nre of a planet where the speed of sound is only abnhaa8)n4:f dk li1s2w 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 8500+/kcg(tq8 7j3p k iug+stm:id m/s strikes the ocean. Determine the shock wave angle it pro+mcqitu7 /d gti3kp (8sjg: +kduces
(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 ql .wlhvzw.a7 3;vx9mwy - sx*$/theta$ 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 k54dnby iny;u(m above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a unin( ;y dyb45horizontal 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 20,000-Hz sound pulsetymar-/1 89 qbo s6isos downward from the bottom of the boat, and the i9s/61stm8 aqroo -byn 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 /js g vohmt35g9 ts*d:are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consb0ak 3-g-ke7dkjz z o(ists of many plastic pipes of various lengths, which are open o7-bk-g(ze jo0 z kk3adn 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 from a person makes a sound clomv b90togcw9 23hdf r;5gpd 5mse to the threshold of hudd53b59rcmfvgh tm 2po9g 0 ;wman hearing (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 h3z(txp3zwv*ps( (i s an 87-dB sound are heard v *izps3w( zt hxp(s3(simultaneously?    dB

  The sound level 12.0 m from a louz voc1o,li(ghk4)vzh f3 yh7 5dspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the speaker(7)g4o olkhv fhc ,ih3vz1 z5y, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 z m)8nutfxr*53 pv ea(W output at 1000 Hz. The power output drops by 10 dB at pv() xe8tmr5nza*3uf 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over their eartx ic8zyhvk t y5a.4;;vb c8os+m pfx xr*13*as. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, ancoy3581vtxb x8;x c mfz+ytaps;a. hr* *vi4kd 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 sysu,rf d,f 3ujwj 03lhv 9n5:bxytems, 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 frequency m;ff 2 f w:wec: rku;l(q3ba7r1$\frac{1}{2}$ 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 w;v 8 0)1xtwrlg qp-g-+ kklwjlong between fixed points with a fundamental frequency of 440 Hz and a mass pjwk0r- gl1k +pw l;q v8t)g-wxer 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 vertica.)x:x/ /pnpvu)b v tabl open tube filled with water (Fig. 12–35). The water level is allowed nxt)).:p /b /vu xbapvto 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 fork?   Hz

  A 75-cm-long guitar string of mass 2.10 g is near a wr*)3,bcysu4ym/ oe gtube that is open at one end and also 75 cm long. How much tension should be in the string if it is to produce rsygoe/mw)*,bcur 4 y 3esonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was obser4d9j.qfmm a*qs8r m8 pgg:hr.iy (-ehved to 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 500–1000-Hz range come 637 am,yekhf/yq c6wing 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 thaw ay 76ckmyh f6e/3qe,t 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 is stationary+p g; r1kkyptfyahv:y((-, yejvu;b3. The conductor on the stationary train hears a 3.0-Hz beat 3;fa(h,vkgk (ppt+uy1b: -e;r vyyjyfrequency 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 Hz. After it z7jdftmme1yxxr-y-: mj9 e 0+passes you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant veloy +7jxjmf1yt 9mre:x-d ez0-mcity)?    m/s

  At a race track, you can estimate the sp7saa jolu osh424 7a-heed 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) uha o -a7j2s4h4osa7l as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, prod z*.fu cjaza rm:2a5k0k) g3lwuce a beat frequency of 11 Hz. The shorter one is 2.40 m long. Hogz *w c rz2u.ak:jaaflmk05)3 w long is the other?    m

Two loudspeakers are at opposite lh+6 xg ci0(ppe1na- nends of a railroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers haa(c0lgpn+ -1ip 6xnheve 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 flow in the aorta is normally about 0.32 m/ n5:d:n gvx-fts what beat frequency would you expect if 5.50-MHz ultrasound:tng :-dxvfn5 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 speed 6.5 m/s while the moth is flyingziilyp*q3,z s h34 fd* toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 *ilysz, 3z4*d fi hqp3kHz. 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 mothk/bp :5hsuv7 rjpir4*h0 ctb(. 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 so that the echo from (/sb:j50tricb4ph ukh*p 7 vrone chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once vpf)p 14tuhu6 nof5g+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 ofho)4nu vpgt6 upf +15ne 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 12–3.) Model as an open tube.

  Room acoustics for sta 5x3pgy:y;wz u 0yzx9ereo listening can be compromised by the presence of standing waves, which can cause acouygpx 9zay 0yzxuw: ;35stic “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 standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involvexf4fy8ov9 k akj 1o)d5s a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is )f1xvkfo8k59ydj4 ao stroked 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 hearing for the human ear at a frequency of ab kh6qw qz ,q2qkh ;71o9btck ixrqa-15o2;kqc9,qh6 k71ko xrzq bah1it-qw 5qut 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 observer on the ground v+ ld5ny 6k7oozeek8 7hears the sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s k el7yoe8v5n6k7d o+zaltitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 1crel6q1(48lpbu o0rq 5 $^{\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