What is the evidence that sound travels as a waveoapeof v79 /uxx 9(hc;?

What is the evidence thatt;9 wpr7wnucp ;i;wb3av d-0*se o)yz sound is a form of energy?

Children sometimes play with a homemade+qw ge-p+u:h t “telephone” by attaching a string to the bottoms of two paper p+e: g -uq+wthcups. 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 the other.

When a sound wave passes from air m,)jwl,8 c.iak4v nfja u-qw(into water, do you expect the frequency or wavelengj4va ,8qnl( fjwi,c.wuk) -math to change?

What evidence can you st2vbz9:jap4tuf*.(y1 n6 2 p vr pudugive that the speed of sound in air does not depend significantly o9v 2 yu 4 ftzbd:vtpj ur6asu*1n2p(.pn frequency?

The voice of a persona2v f7mdbf8h,50 fg+gmoc m8 m who has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of ktcuhe-uq rodhb6. ( +0g*dv/ *xq1fzorgan pipes?

Explain how a tube might be used as a filter to red,o1. +lmnwi:l , t+kjeivd;luuce the amplitude of sounds in various frequeu:im1,lv ;,.e+i nw ljkdto +lncy ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30+ +b 2 cmyshj6(wnekb:) spaced closer together as you move up the fingerboard toward the bridge b+:y6(hc2k + wnjmbes?

A noisy truck approaches you from behi rwx/n+-h/uo8r zda7ynd a building. Initially you hear it but cann8 7zarhu-do/w+rx /ynot 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.]

Standing waves can be said to be due to “ii-pue0ijqeg1t::w 9n nterference in space,” whereas beats can be said to be due to “interferenceqi -9 une:epw 0j:gt1i in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would jrjls49r +m:nvpz9w 2the points D and C (where desmnrw4z: s9plv 92+j rjtructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who work in areaskydc3opt6i 2bnc( 0a9 with very high noise levels have consisted mainly of efforts to block dko ( y9b2iatc036pnc 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. 12–31. Eac bj3:jc)jp 0;xsyl3 wjh 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, (xb 03;yj jjp)s:wl3 jca) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler sk(s(ne.nc n3wn7,li(4 yrged hift if the source and observer move in the same direction, wy n(nr(nse.,cei47n 3dgl w k(ith the same velocity? Explain.

If a wind is blowing, will this alter the frequoni*t0 j1thsv) j.,.j0,y qr: rmnprt ency of the sound heard by a person at rest with respect to the source? Is trj0p .m jyt:)1tn ij,t.h0 q,nrv s*rohe wavelength or velocity changed?

Figure 12–32 shows various positiosuj 9kv/ bcby+q:: i1usi u2p.ns 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 th91:.v:jsup/+cybuu i k 2sqbie highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake bye *)gf*s llgbkt-rb1a 2 8ouv3 listening for the echo of her shout reflected by a svtr23lu b *akf8g1-lbgoe* ) 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 s+:w ys3: egtvjust 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 at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary s:3 g +sw:estyvignificantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths inm)f nm9zc;6 bt 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 abovy202o+b,tp te o*ssi+w soq0oe a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses befossow,02 +t*pstioobyeo+q2 0re 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 d:p0 hfn4 g 7*p p43avfjdpp:ustriking the water below is hearh07pp a 4fvungpp3f4d::d*p jd 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees9tee bs8z vl;9f2.bpaz lc b;7 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 1.1 s apart. How far away did the impact occur?se;9;tblv287 acbfz.pe 9 b zl See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-. 1lcrau d0rz q,+ixa-second rule” for estimating the da-.xa ,+1udrl0irqcz istance from 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 level of 9w hpdmp a+p;aei21a1120 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 wh-jblu iyf* hkhne2h)d1441 c nose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneous r)x tpe8,6h ngf)wz;rly at a certain place, what will be 6 zrphrt)8)n, ex;gwfthe sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane w93z*ikd; ,emg l*p 0ls c/6j nkjx/eghith 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 inh;6,0i jp/k lnlgkjm9z *ee* x s3d/gctensities, not dB’s.]    dB

  A cassette player is said to haev/zl6iw; k wj gns+rd (*dq-2xni,4mve a signal-to-noise ratio of 58 dB, whereas for a CD player it is g-msd( w,qv2 + jik4x;indwn*l z6 r/e95 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 of sound from a person speaking in nor*js7:n- e ((dom) qoymk3qkabmal conversation. Use Table 12–2. Assume the sound spre73yk(somq an)j:m k (*boe- dqads 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 strikesg7 az6 q4x8*nhjdk hys crq;b+mo+3-q 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 zts6qit *t,9.+ m pm efebu-c:is rated at 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level i- . tp+,:96qem fcuitztbsm*e n 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 p 1pr00;xuat,x5gfj wvs j(4:g4cp +xe ba5sttlaced 2.8 m in front of a loudspeaker on the stage.ws(j1a pxg5 upxs xtg ,44ft+vtb;j5ra00: ce
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound lee.em u :z-w f.kbecctg1 6(p8pvel of 2.0 dB. What is the ratio of the amplitudes of two sounctkez.81-gpwb ue :p 6ef( .mcds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the i,sfbi+7zx6vat yw )0 zntensity increase z0v) +tfxay, 7bi6zsw? Increase 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 twihrnmboxnsi z8 52, 2vg0l5y;gce the frequency of z ggyli2h;5, xnns2v8 0r5bmo the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that corresponds tb )gh+thu)*zg/brts f;k pk/ 4o a displacement amplitude of vibrating air molecules of 0.13 mm at 300 Hhrbu) ptt/zgg/s*k;f4 +bh k )z?    dB

  A 6000-Hz tone must have what sound level to seem as loud a: qb16zhlvonc, yr3;,25vsrg (hobcas a 100-Hz tone that has a 50-dB sound lev;bh, rlc 6v(ob3 goycr15sqn,:ah zv2el? (See Fig. 12–6.)    dB

What are the lowest and highestzdb0:;3d8 ;sy5hys5urw jcgp frequencies that an ear can detect when the sound level is 30 dB5 5pb 0jcy;zud wg s3;rd8:ysh? (See Fig. 12–6.)

  Your auditory system can accommodat2de f ss:gv9p,5;yam ce a huge range of sound levels. What is the ratio of highest to lowest intensi;5cy, 2 pevas df:g9smty 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 l:kkd 6.ssdd:gength of the vibrating pordd.sds : g:6kktion 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 l0l )vf pv52ytiong. What are the fundamental and first three audible overtones if the yivt2lfvp5 )0 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 acr;e/6;,m (h gi.rpse wsvr5 w.lzyyqo*oss the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed ts*o ..z,s/ 6ei p5ml ;(yyh;rvwrge wqube?    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 spanning themt btr+:- /kdq range of human hearing (20 Hz to 20 kHb/kr:tmq +-t dz), 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 73vrd5 owt -nga frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its or-5 vnwr7to3gdiginal length?   Hz

  An unfingered guitar string is 0.73 m long )9x d9nuko i-,;zxfajand is tuned to play E above middle C (330 Hz)oaniuf-; jd9kx9 ,) xz.
(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 thpt24(f / 9bh,kfbn m2codqwu ,at emits middle C (262 Hz) whenck9q f 2du,b(b2o/fn,hm t4wp the temperature is 21 $^{\circ} $ C.    m
(b) What are the wavelength and frequency of the fundamental standing wave in the tube?    Hz    m
(c) What are $\lambda$ and $f$in the traveling sound wave produced in the outside air?    Hz    m

  An organ is in tune at 20 b4 dk6-hd :m4irb 0x-zv n;myo$^{\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 be4 c h ppg57 /(fpb,fx+qscn,ze that must be uncovered to play D above middle pcfhc/qpx, sp+zf 54ng,b7e(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 resonareuw w8 ps6xb65/p. syte at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (awep6y6x8u/ssbw r.p5 ) 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;fypmif5 3zn3( xma /x.3djyz7fl)tu open at both ends. It resonates at two successive harmonics of frequencies 3lfpym53xm 7uzzdja3y fn) ;t(/i x.f275 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 rc3q cdu) ga; bq.(ypsy4 f0q.$^{\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 aud xgck0rr74 el9*t5 xroible range for a 2.14-m-long organ pipe at 20rrco094*gl5kxt xr e7 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5c ;d thbrtnsw9sfx3a0: s/w */ cm long. It is open to the outside and is closed at the other end by the ear sc/*sbn9r3af:d ;/xtw0 t hswdrum. 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 Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat zce* j7k -:fpxevery 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. f-zxk7j cp *:eHow far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz) anv hmvf5 l5z/k)t3n.h2e *pngik y8m 0od $C^＃$ (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 (brand X) operates o 0fgksa);mo+ at an unknown freqfs omagok); 0+uency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounde ,(s-ulca ao;e:)b fivd with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hf)aleboi;usv (a,:-c z 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. The tenskmqlp/u/ ;kk fk 9)n(jion in one string is then decreased by 2.0%. Whatmp)k;/9u q/nk (lkjfk will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be3 g)krx0 dc4r*xdsvdlh +qy( ; f32nlo heard if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C axd ;(cohdl0 sk +2*d3y 4vrnlf)xgq r3nd the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B (mq2mbr0h -ir7b64epm 9dg-ff ,v wri has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded togf- 4g0q,mbb de(r9p6v2mwr rfmih i7-ether, 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 3.00 jf+iw ;v jtf/( u,+wjgm from one speaker and 3.50 m from the o+v+jw,igw u f/t;( fjjther.
(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 1v5rljs2 61brd83 ssv) fel d2k32 Hz, but a piano tuner hears three beats every 2.0 s when r) 8s2df136kjd sr e5vllsb v2they 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 waveyfc b:sp)0ch 2w9q7sjdl -fa4lengths 2.64 m and 2.76 m in air. How many beats per sejw0ahf2c-7)d:4f pqcyssb9 lcond will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire en s.zl6e,h)n6)bf (yxqsi :vaagine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30 m/ss.zbqy ef h(,a n:saivl)66) x
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still ql tz3u 1;vlh1wuumtp22ew),. What frequency do you detect if a fire engine whose siren emits at 155 l ;v pl u,1uw3zq2muthew1)t20 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequen 3c/0wlmj t+yscy if a 2000-Hz source is moving toward you at 15 m/s versus you moving towardm+/lc0j sytw3 it at 15 m/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 frequg0b;m-igpb hs6; hea0 9lcj9bency horn. When one is at rest and the other is moving 0ig0gbp;96b c jhelba hm;-9stoward the first 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 ulp0:x7;9zeul ap en) ultrasonic 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 sound frequenp a7n;uz ex0pll9e :u)cy?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speniv8km), oszn m v+ e5n0:crl)ed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bveimosn nk05: )8 rz nc,m+)vlat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving fd,tyv*)dgqcw)to ) r6/w;y ujlat train car at a frequency of 75 Hz, and a second identical t6j);d* g/oy,cty) tudv) rqwwuba played the same tone while 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-fl hrjy88; wdr, h.ljh:+trd f;uow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is floy8lh;:w+, ;ftj hrhdr r8 dju.wing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasok:9xxump 7xeue p;8k2 nic 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 frequency 570 Hz. When 9u6at djk7si gzwakao e2 2*)i+)lh2 *mmdff2the wind velocity is 12 m/s from the n)s9 ahj)ai u2dotd*2f27*+ gwfim lza 2m k6keorth, what frequency will observers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if its speh 6b2bnw fsd)wenh*9;ed 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 where the speed of sound is 310 m/3,br vdoi rti:qg* um)or v+,)s (a) What is the angle the shock wave makes with the direction of the airplane’s motiovgo,3 * iq urr,+im)t)obrd v:n?    $^{\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 .quql9fa7r l :vwqzf-gys 493 a planet where the speed of sound is only aboutr7zvw-quq al9fl.g:f 43y9sq 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 ocean. Determine the shock k0e9zap48 de3 k/xjanwave angle it ppd a0kke 9jzne3xa4 8/roduces
(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 jh-atc+); j8xg7 waeh$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a planw.t2tcne0t; 4/6czr e-5)onqv y/ p /ii psrgpe exactly 1.5 km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal distanc ; 0rgwyeonp4cctq s 5-in pv/r e.pit)t/2/z6e 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 pulses downwas5j9 j/mo2+ 8-dnjow v+ eriqeo7e(gt rd from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed twn(2 qi r o soee t/-758j9ovmdejj++go work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible qkn+fq+ 0a7ubrange? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sicw8 )d(:ci gzewer pipe symphony. It consists of many plastic pipwi8 dc :i(gcz)es of various 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 m from a person makes a s uoelj2x9+ at3ound close to the threshold of human hearing (0 dB). What will be the sound level of 1000 such mosquitt x+e32olua j9oes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-/ +8 9/r/ /fy0rxgmyima nzmfodB sound are heard si//famnm+zir9x/ yfy8 r0m/og multaneously?    dB

  The sound level 12.0 m from a lounv. , r fh d0jz):vlwvx9(xmbcd1/al9dspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the speaker, asshv(0r/:n9 zxwjv9)m. ,ld da cb1fvxluming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. T; 9c:uenmhbn8atpg 08xk-+ug he power output drops by 10tghxnug+8u9e mnp:8k;-ba0 c dB at 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over theik( lv)n6+lyxms601rt5k wi 2dp +ekjir ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the aewvj t)6lxis m56dp(k ry k++kl02 n1iverage 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 communicas cny5bb bc984tions 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 frequenk1c,r) (gz)u6iv c dejcy 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 c 3qc:/2xg3 u9odqtpn . 8oowrfixed points with a fundamental frequency of 440 Hz and a mass per nu 3crgt qq./3w8 x:ood2poc9unit 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 abov 8 qk/x2db/yt (.hwot94tzfhge 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 k/qo248wh/ dhg.9fzt(yxt tb the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of;s4wjsoyi p)flic -6 kko4+6b mass 2.10 g is near a tube that is open at one end and also 75 cm long. How much tension should be in the string if it is to produce resonance (in its fundamental mode) with the third harmosplis; wk 6j6k +4fi)-ob y4conic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one fu4aie ds 6cdu54ll 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 from two sources.. b0u jaf/f8dyb,kqi b:g6/usjyh7q2 The sound is loudest at points equidistantd/0/ 7bj kyiasfq:y8f6u bh.qgj bu,2 from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistle uhs5u mm6vz 2u8.7syes. One train is stationary. The conductor on the stationary zue7uh8 5su vms6.ym2train 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 csau 5u)c8p+9 *hpcl cwhistle as it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How 5 ccc uu+ slh8pap9c)*fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can es*dc 59k 0zbtrc2un:oyham(b *timate 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 (freqyrzoc hk9t25 n0bd *mu:(b a*cuency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequ wg1lz *+egio y-sox,7ency of 11 Hz. The shorter one is 2.40 m long. How long i+wx 1s i*gz-,7 loeoygs the other?    m

Two loudspeakers are a9wjjxp /kz;m8 a,c*e nt opposite ends of a railroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listens from the position A, in front *9 jpe ,nwjk ;8axcm/zof 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 cyj2: ef c vnlt302/bc ra6z0iaorta is normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves werc ybv t6zj23l rcn0i/:0 f2eace 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 flying tg5 aq7hwm1q0 zoward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of the wave detected by ta10z h w5qg7qmhe bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound pulses as it approaches a 4bsm)+ (no 5zrfb*vawmoth. 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 one chirp returns before the next chirp is ev)w4mnb osz f*5b(ar +mitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signals from one Alpine villar5pn6 o k,x6jnge 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 fn j6np,o56xrkundamental frequency 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 compromised by the presence ou .)dxagrxnx,j vl49 ;f 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,alx. dr4x 9 gj)nvxu;, 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,u/.qhh cnw+ 1jrwa*2o ” involves a long, slender aluminu owh*rw2u1a n+c. qh/jm 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, 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 thr*9;gem*tv9 zqpw kbb+qq( 1rt eshold of hearing for the human ear at a frequency of about 1000 Hz is 91;qwkb * *tpmg+t9qbz (r qev$I_0$ = $1 \times10^{12 } W / m^2$ 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 vrr4ce/b rw ,9ground hears the sonic boom 1.5 min after the plane passes directly overheae,9r4v w/ rcrbd. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 1ym6uwq w-b5zx5fp 9 dr 7*go;o rkk+)n5 $^{\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