What is the evidence t3v.0u+ y)dm3sy p9z8q c hzkiphat sound travels as a wave?

What is the evidence that sound is a for3p5b*es i cl28pfouynn/m(h fnj1 a1;m of energy?

Children sometimes play with a homemade “telephone” by ujlq5. :b.a) ti87k kdp+b forattaching a string to the bottoms of two paper cups. When the string is stretched and a child speaka )ut +d7 .pb.:r5jqki8kbfl os 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 frequency or+/q.ydocp j) b lvv3(j) x6jpk wavelength to chaj jly )pvp+xb/d)(j6.k3v oqc nge?

What evidence can you giv5c *clo4jig1l+7r t/. kshchne that the speed of sound in air does not depend significantly on frequen*h ncg.hsi1lt+ co 4jklc7 /r5cy?

The voice of a person who has inhaled helium sounds very high-pi8pv85, d xrzzxbc1 4drtched. Why?

How will the air temperature in a room affect the pitch of organ pi 43/t x zeo vi)-2 kvd4bye7yhhbn;(yqpes?

Explain how a tube might be used as a filter to reduce the amplitude ox*n - gb hw.l0fcte/k9f sounds in various frequencyt0e n/c*-fhl9w xb.gk ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer togetsm m*r z64um;jher as you move up tjrumm *s z4m;6he fingerboard toward the bridge?

A noisy truck approaches you from behind a building. Initiall+eqhx,11 xgq:s7f zcm9m6umi y you hear it but cannot see it. When it emerges and you do see it, its sx+6s:7cxz gue1 ,mq fiqmh 1m9ound 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 “interference in 5/ yqauyt3;;ecb*m8hy j a.pw space,” whereas beats can buw/85y3.;a;qe ybcm tjy p* hae said to be due to “interference in time.” Explain.

In Fig. 12–16, if the fr6to.r p:9 m ;ip;c/yynvefy:ixs7r x 9equency of the speakers were lowered, would the points D and:x.o pry9 rp:ye iv7si t;y6n9mx;/fc C (where destructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people wh9hse+zo8;jrmxxk*03 r, g dowo work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to t s+m;jwh8g,rkd ezo9 rx 0ox3*he 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 xt/bq4twdq b4 6h*-vd(rup9zr0ev 4j –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), are the two component frequencies farther awqj b(d6*-uvhrp 40z 4 tvtrq/e49dbxpart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in tobr: blp 1a 1+je*smb,:;yedvl :.bam fzsu9-he same direction, with the same velocity? Explai.,-*l9+v;:ea:ob j1d bmse:rsbubmy1pf zal n.

If a wind is blowing, will this alterz2+am /slqcab7qh,/ro0m a6s the frequency of the sound heard by a person sa ha62b,om/7qm0/lr+cq zasat rest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on u7 jzill p(s05;ffpc5a swing. A monitor is blcisj0f7 f5lp5 lzup; (owing a whistle in front of the child on the ground. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by fviq6 8j7n67il2im h flistening for the echo of her shout reflected by a cliff ativfn77i6 mifq2 j hl86 the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He hears :0k5:.cya:sweo k)r(wzarn othe 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) aazk.ay5 es w r:owrn)0:okc(:nd does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths or7lbg/4y z:ehb-k 8r zym77hf*lu-bki )4mq 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 above a school of 6l+l tr(b xl)ctuna 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) blc+)x6t(ll br y the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes when5nm4 pr st*,nu striking the water below is heard 3.5 s*t 54pmurn n,s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a )qx b(p-;svaze- *gpu huge stone strike the concrete pavement. A moment later- u(*b ppx-vqz)ga;se two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-s yxgyrj1eo/w8 ,j axrh-f)(63qts+ieecond rule” for estimating the distance from a lightning styg-/( iqh,xsjx8jyweot)r a36 fe+r1rike 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 1rr, 486njjax j20 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound levellrv1 pd2d- q*j8hr i2f of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneously3b75q/hpdej ym xitg5oh 1* e* at a certain place, what will be the sound level if only one is exg ehy3 51m7jx*he5q*ibtd/ opploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally noisy jemtu:c/zw2 c-as. r cs,t engines is exc:/ uccwz sm tr2-s.,aperiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas)+b,rt og: cb9a,u o;y77;cjz hlczra for a CD player it is 95 dB. What i;o;yzloc 9bgr,rc:)b7 t7u jzaa+hc, s 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 normal kz13o.q45g ;t r q7 lnr(egefaconversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphe.e(nof;lez5t q 3g174gk rqar re 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 eardru0: q)o.;;d qcb gfohifm whose area is $5 \times10^{ -5} m^2$ (a) How much energy is absorbed by the eardrum per second?    $ \times10^{-12}$W (b) At this rate, how long would it take your eardrum to receive a total energy of 1.0 J?   $ \times10^{ 3}$yr

  Expensive amplifier A is rated at 250 W, while the more modest amplifier B gs8ft /rcr(jp+f ;x a:is rated at 40 W. (a) Estimate the sound t;+gj rffs /crax:(8plevel 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 mocxjv v:rui.: lt4 a:,7k,smp5lj3 m in front of a loudspeaker on the sta:kr3j 4,7v vo :sm5mpualc.xi:mt,ljge.
(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 typic w18, vi pn*2kovrz2ng ot:of.ally detect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Se vgz*:,8n2krv2opn o 1.tfowiction 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will 1,zttax kb 76hthe intensity increase? Increase by a fact ax1 6zk,hbt7tor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one hd4 vag9fwb ;y y77nn6was twice the frequency of the other. Whad6gnbnvaw 47w;7 y9 fyt is the ratio of their intensities?   

  What would be the souw3n- -cig ;kwwnd level (in dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13nkw- wgwc3;i- mm at 300 Hz?    dB

  A 6000-Hz tone must have what swo. , 0syf(5m9pd)1z.sokssi+cxb vl ound level to seem as loud as a 100-Hz tone that has a 50-dB sound level? (Seoyo mid( cwf5 z9s1)0s.sx bv+s k,.lpe Fig. 12–6.)    dB

What are the lowest and highest frequencies tzk0ivg 2a7mf( hat an ear can detect when the sound levelgz(2af0 v7km i is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a hugem xj,ksx3x36au+b9 bu range of sound levels. What is the ratio of highest to lowest intensity at 3j 36u xub,+xxks9ma b
(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 freqube u99l px/j6trfk2fgiez640 ency of 440 Hz. The length of the vibrating portion is 32 cm, and it hi ur6gjbekz96 f/90l 4xfte2pas a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm3zf aq* bdhz5vy d:dug6 kp;54 long. What are the fundamental and first three audible overtones if by :zhduq6a3v fp5d5 d;g*4kzthe 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 frequencyro;-gxm dzp3;u4 ur+ o would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tub; r zpur 4x;o+-3mdugoe?    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 pipesj cqt:ptyh2/ 1x,q5d,zut5hd spanning the range of human hearing (20 Hz to 20 kHz), what would c,x:j521qqh,y ttz ut d 5/dphbe the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmonic. What wi(,qksl f 1 gltzy3;2it eo-:rlmo-w8ill be its fundamental f t1fe,-qsl( woitmk2rli 3g;zo : ly8-requency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long axe.k3qhaa*- mtn7v8o vp,d, skb)j e9nd is tuned to play E above middle C (330 8m73.t) xskkq jpav9de b,v,nae o-h*Hz).
(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 tnbt0np gx/u* .pj 7eh0hat emits middle C (262 Hz) when the tejhnx 00/b*p7.gpe ntumperature 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 pdcg7dob y*bjs.3c kh)g;8-j 20 $^{\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 1-oy24 dvrepgf 4+s9irt3qb+ e2–10 should the hole be that must be uncovered to play D+te gpy3redf i2o9+bq-4rvs 4 above middle C at 294 Hz?    m

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

  A particular organ pipe can reso, t3k,u4syxrp3o 5zwh nate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Strh3 s kuwx y,,4z3po5how 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. It l jplaox1,5w6bu44 57knfv bp( mq6garesonates at two successive harmonics of frequencies 275 Hz and v 1xl64 n,b4agp5 mkl uj(qfo7abp w56330 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 rozl i57 2kc)qw:wmq*qh2,d b$^{\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 muci):p:l .: wo oqu-c6dq8,:pbbnzcpresent within the audible range for a 2.14-m-long organ u p-zulqbcw:,on8 :6c.mb d)op: c q:ipipe at 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 ou1vlk1xakmc/pv y npnx1(3y)hi+w7 1i /utft6tside 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 Fig. yum1i vihy)pvxkwt k117 l/(+npnf36ct1a/x 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s whengar 7y 9iq-phsn 0v(s9 trying to adjust two strings, one of which is sounding 440 Hz. How far off in fnhir 9p9y0g avs-q(7srequency is the other string? ±    Hz

  What is the beat frequency ir /mdm-jr/kuz0y 1u9+vy85 hu s f5rwnf middle C (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while 9y,kfh.b sds*another (brand X) operates at an unknown frequency. If neither whistle can be heard by huma9s* f dy,hb.ksns 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 hb487mf;ckyygg g,( ibeats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 35mc,4ikf7hg y g;g8 (by5-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the sa/*4wz peyqbez;92 jf/(mbky fme frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What wi 9zf4e/e2ym wfkjpq/y;( *b bzll be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes 42spr z(fv)e teach try to play middle C (262 Hz), bpterz (2 vf)s4ut one is at 5.0°C 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 4u()fdg 6 f kets4-+1nd9 -yfy gwynml341 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beatyfm)s ygy d-efld 9t-+kg63n4 f( unw1 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 m from one speaker e*)930)h zzuu g jfb;fa1pgnnand 3buz1gf3z g;9h0) pnn)j*ufea .50 m from the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are s, lsyi5iu3+po upposed to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibral+5 i,3spiy outing 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 an6 cx0rkcex w 89yzv/ve9 x*7ycd 2.76 m in air. How many beats per second will be heard? (Assu 8e7yv6ez x*99cc0y /kxrvcwx me T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s sr n6 2c.uo.hqq2; ;stnjru:bjiren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30bhjncj r2su2q.u. :qnr o;t;6 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you/;dp)zohrq2 co)btr 5 detect if a fire engine whose sirezor b;/doq t5 hprc)2)n emits at 1550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency y (o*s9i1 umx5jcqt .qif a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15o9j* m.5c usyx(q1iqt 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 frequency horn. Wmg1 -w ;u.kj6r(jgw9cbf fn mlg3l *)phen one is at rest and the ognl*u(m)k g glw. rb;3ffwpm 6-j 91jcther is moving toward 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 ultrasonic sound waves at 50.0 26d3jlmo f-d qny2p s(kHz and receives them returned from an object moving dir2 6pfo2nyls-(mdq 3 djectly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at n-0x 1mw0yi). nj0 a75ddo(ii bmjoeu a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bay (701du 5amo-nnji0oixm.j0id )web t hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving flat hjcrbrcr6 6vyjr*6 jz+ xq)75 train ca6xh7*+)6c j cjjvzrr r 5ybr6qr at a frequency of 75 Hz, and a second identical tuba 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 mea 5z tk 9hiae0csym7s04)8nb c ttt+du3sure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound sonttte t sm+a3cisczy9 054d) 8u70bhkurce?   Hz

  The Doppler effect using ultrasonic waves of frequency 4)n g0( 8vbfoned )zyhvpwj ++ $2.25 \times10^{ 6}$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 fre4.zabrp0nji6 quency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear wpijr64ab0 .nz ho 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 it..c6i u a te7kl.wje/ps 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 Mach 2.3 where the speed of sound isw yd/- 3r7bxtn+wxkmq f2u.t/ 310 m/s (a) What is the angle the shock wave makes with the dy + kb-qd/3xwrwtt.2mn7uxf /irection 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 planet where the speed of sound isx v -3vnafp(n1 on1px ( nvv-fn3aly 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 strikes the ocjxc dh,;b9)auoik.* tean. Determine the shock wave angle it produce9ui h;dkob c,*j) ax.ts
(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 mr0cv;cuqw av756t +m$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overheat9zbrl1* u)l ld and see a plane exactly 1.5 km above the ground flying faster than the speed ob*)lt9 lrzlu 1f sound. By the time you hear the sonic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 12–34. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device that sends 20,000-Hz sound pulses downward :- 5kl7z.f:hite dabv from the bottom of the boat, and then detects echoes. z: .7feb5la h:vt-d ikIf the maximum depth for which it is designed to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are n9*qb6ls agm9there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists0l0gi qg /aj9tib )6fb of many plastic pipes of vi9)0ljg6gb/ if 0bqta arious 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 sound close to the thre3,qafjw t +vs/shold of human hearing (0 dB). What will be the s,j3ta/fs+wv q ound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and arp1ccuq;c q1k w d +4iq.;:jhwn 87-dB sound are heard simultaneousrc4p wqj;wiucc +1:hk . qdq1;ly?    dB

  The sound level 12.0 m from a loudspeaker,mom5te*6*xd z placed in the open, is 105 dB. What is the acoustic power output (W) of the speaker, assuming it radiates equally xo zem *56*mtdin all directions?    W

  A stereo amplifier is rjaprkofx 1:4q 8aiw :4n w;6ymated at 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power:kaf84w61q ;rx mjywna:i op4 output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protwz j(8kotwr5) h *rdy:h enz9 m-r1x/fective 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 distance )t9:xdjo/n(m1khy 5 rr8zez*-fwhrw of 30 m from a jet airplane engine?    W

  In audio and communicationsv0w8o5dph5ys 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 tts47jv: xc6(d zfcfr8d0 qc7 uuned 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 fundamental .t;r(x rd6 9runkrug( frequency of 440 Hz and a mass per unit (kr;rr9u(ndt rx.6ug 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 vibra,86rwh xii*a.q4 kbzttion 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 0.12,h.r4w b*86z kxaqiit5 m and again at 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar stqjl(khwo (w9.-o wvw)sj d :u1ring of 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 proj .uw dqo(wo9w)jvh(w: -1k lsduce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observeih myak1 6ys,)sxm z8:d 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 tonf r/k1n+ek2r jmnd(j2u1 2sjfe in the 500–1000-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 minimal at a point 0.34 m farther from one source than the other. What is the frequ+kn1m2e /(jfr urd f1 n2sjj2kency of the sound?   Hz

  Two trains emit 424-Hz whistles. One trainuu p(udmd)s(er t ep(rtb(3fmy5/ 3-q is stationary. The conductor on the stationary/(frmt used (ytd3(- 3)(u5ppm bquer train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approaches you is.9yw( j5nwmvj 538 Hz. After it passes you, its frequency is measured as 486 Hz. nyj(mw 59 vwj.How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estim ymc-4devqv pip8 417jate 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 ce8 v m4p7d4 v-cpqy1ijertain car drops by a full octave (frequency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequegkpu q9gn-o3-r.p6 ;zg,p lioncy of 11 Hz. The shorter one is 2.40 m long. How lon9 . pq3oui kgzgrg -6on,-p;plg is the other?    m

Two loudspeakers are at opposite ends of a railrowng-,)fbh5i 8km/q xrad car as it moves past a stationary observer at 10 m/s as shown in Fig. g-f5mkiw b8,x)nq / hr12–37. 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 flow in the aorta is normally about denq*7h lsg.*+ k*w6t hnf 3pu0.32 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? nsq* *duh7 he .w6*ftgk3l+npAssume 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 mo19ihaai j5) ifth is flying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of the wave deteh19i) ijaa5ifcted by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency s w0th,8ds( yx 30sdfyuound 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 so that the echo from dtfh y(u 3d8s y0s,0wxone chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signals from one Alpi; zi, swppjp;)ne 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 zp,ppjs;wi ; )in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundamental frequency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be compromised by the prese7(e2ulmhx nnx/mbo )f, 0piz:d-h8lj nce of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4 l )lp/xijehzx82-mn mn, d0buh7o:f (.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, b(czxejad0l.:omxbf /- w7e:( g9 vddcalled “singing rods,” involves a long, slender aluminum rod jc0(l9d.ab:ge7zbvf-dxx o (dm /we: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 threshold of hearing for the human ear at a frequency of zgdz,k vo qha8 ,+o:(jabout 1008dzko(z :+,q ,vgohaj 0 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 g5cp1y ap nhe se .0lpg-ct.j/jd6+ 1lqround hears the sonic boom 1.5 min after the plane pc+1-tc0e51 hqjslnl/jdp pagy 6p..easses directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat ismlf9 .kf6/m2sv du*;fhewab/ 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