What is the evidence that sound travmhd1go5k yk:9gza:4j8m o1cn els as a wave?

What is the evidence 47 /z 6e-kq8kmzn3v ttkmp4snthat sound is a form of energy?

Children sometimes play with a hsnn- ba47:liik* jln.a59wedomemade “telephone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly howw:95sejbnian- 74l ali nd*k . the sound wave travels from one cup to the other.

When a sound wave passes from aireu)ncrht a w4 z6,,s8dj8(aulj7xv.b into water, do you expect the frequency or wavej , sa48etv jzrd8u) 7c6,bhl. (nwuaxlength to change?

What evidence can you give that thr)exfl5g oxq 6(l8 cdq,5va0ge speed of sound in air does not depend significantl c l,6gle5adxgof5(0)v8qrxq y on frequency?

The voice of a person who has inhaled helium sounds very hdwd0cd n98;, ix0bd3hfel 4 fnigh-pitched. Why?

How will the air temperature in a room affect the pitch of orgj:o(efcq nr geojn0-n+t0d38 an pipes?

Explain how a tube might be used as a filter to reduce the amplitn2j rcxj,jny5(r j-j-ude of sounds in vari2-rcj j,x(j-jy5 nrnjous frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as *jxyb di*cq d-9w4- ppyou move up the fingerboard toward-wd ypbq4cp*9 x j*-id the bridge?

A noisy truck approaches you from behinamp4/;0oj9 ewg w;) vypyixgp0 / nk8ed a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 0pw4)gvno e kg/; 9x/8 w pjy;ymaepi0on diffraction.]

Standing waves can be said to be due to2 hv s3. m3arij 8e/whq:dkwkn s+p3+w “interference in space,” whereas beats can be 8rvw3q.d: 3w2kj 3e/ +wma iss+nhkh psaid to be due to “interference in time.” Explain.

In Fig. 12–16, if the p f +v)c48qqbp6gfo5pfrequency of the speakers were lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or closer togf5 qgpp48pco)+q6 b vfether?

Traditional methods of protecting the hearing of people who work in areas wim3-h 0d(g eqt9ldp5al4z4gtb th very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new q0b43zdgltale 4h 5dm p-(9tg 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. 1n;d1*c7xd ne6mkg6 r a2–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In wh mxae 6dknn6g7*c;d1 rich of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer movz fnywa; +xo2.h pr,a6av.j3k e in the same direction, with the same velocy. k wah+xaf2rz,n.o pav;36j ity? Explain.

If a wind is blowing, will this alter the frequency of the s-sw0m.e5x rri:(ln msound heard by a person at rest with respect to the source? Is 0l mss5:rniw( mer.x-the wavelength or velocity changed?

Figure 12–32 shows various positions of apr/8 w5jhbpv/ a4-j bd3th,xi 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 frequency for the sound of the whistle? Explain y ha3j/4btp/ 8i5xh,rdwb-p jv our reasoning.

  A hiker determines the length of a lake by listening for the echo oao.8cvy 1(g3cohlqj3 * a-oyqf her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the len(*ov3 coljy hqga o1 3a.8yqc-gth of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below thed(rbpe6 o5 p 706 cg0bpo0csiz waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 ssb0p0pc o (do6e67bz r0gc5p i later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in agt adptq 8+88l9 4,nqcwm,rmc oje5j2ir 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 driftysmb4 t m1; kfg.:w7qp28 lvxvbhm1i6ing just above a school of tuna on a foggy day. Without warning, 6 f8 .2tmpbx4ymli v;7w1qg1m vkh:sban engine backfire occurs on another 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 sp/4ap3 ngz2 nvulash it makes when striking the water b3gp 4/u2vn zanelow is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone str1 dhrsu66 x23t4 qwqzoike 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 oo wrud2qxz q 661t3sh4ccur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent xf866jkylz np kfj6o*5 0xta9 error made over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the t 68fzal 5o kj96xkj*txy0pfn6emperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain levelk6o4 p-wil3m o of 120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of a sound whn w7gg ) tzx8:tzx(s3egh*w0g ose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce lw3zm4t f(t2 ya sound level of 95 dB when fired simultaneously at a certaim(wl3yf 2tzt4n place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain+ g+1sj8n*si gkj/k id distance from an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensitis ndgs1k +ij+8g kj*i/es, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, wherobgrs ,.sgh 5- gs5bx.eas for a CD player it is 95 dB. What is the ratio of intensities of the signal a s,ssorg-g.bbh5g . 5xnd the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound fromuad 9w ik3i(ug*c2p4x a person speaking in normal conversation. U9i uw4acd2i3u*pkx ( gse Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the mouth. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave strikes an eardrum whose abjfrf,fyd7yaq /jti w (4:6.grea 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 morx+ af8w/3+txea fk6 tke modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a /8kxa+tt kxff36aw +e 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 place3u3 ts1k*b0 equlsd:rvw4r6v3prxd .d 2.8 m in front of a 16.rtqu3 l4dpsv 3* 3r reswd0bxvuk:loudspeaker on the stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound lever tm 2lbml11m-l of 2.0 dB. What is the ratio of the amplitudes of twl-1lrmt mm1 b2o sounds 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 xspe, )lq.b*iv j0b.t will the intensity increase? Increase by a factor e0 bs,.xbp *i)jvqtl. of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has 17b kld i(h.+k3h vslstwice the frequency of the other. What is the ratio of their intensitiessk1 h h+klb7i 3d.sl(v?   

  What would be the sound level (in dB) oqki,h.cgld5( p ucd.7 f a sound wave in air that corresponds to a .5lg(kdd,uhp.ci7c q displacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem x h4dz8t4p+emm1 oe+(4 tbvxkvyf5l ; as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. (4;t x4e1 op+d zx vk fl+m8tvhb4mye512–6.)    dB

What are the lowest and highestxc indi9*v 2(i frequencies that an ear can detect when the sound leveli (d*9cvni x2i is 30 dB? (See Fig. 12–6.)

  Your auditory system hkf+it,x1g 4hxk. eht ctydz.u0 ; /c)can accommodate a huge range of sound levels. What is the ratio of highest to lowest intensitygtxx e..k /ttz hiyh01f,hc+ u)ck;4 d 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 freque* 8c 0,3a0ynrsh5dpj b-q.osv0ailjt ncy of 440 Hz. The length of the vibra ,tn*-a3q0ob.5 c80pajdih y0 lvs srjting portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What arew 9;3mpf.hjwso 5vr*g6pwm ; g the fundamental and first three audible overtones ifwfg.w m35 ;r*pgjwpo h9m6s v; the pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you expect from blowingceo/phy/(dy ev4+tdx ekz0;y 6+ q (wf across the top of an empty soda bottle that is 18 cm deep, odvy;y6h/k /4wtfz0x( +qe pd+(eeycif you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-te ...dd9v +o70oec-tn.i pxi(md hhy xube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the len0 7xm.noi( y. hi dx9dcevdoe.hp+t.-gths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string kwuv auw6g8 cfu-g i8x jm582f5b55xphas a 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 b85 wxw8pc2uj5-xukgvg5a5mf8i6f uits original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to playt./jvo mv,zki)+ 1k qr E above middle C (330 vm).t kr/zkq1,vj+ oiHz).
(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 ola4q-8 vzq: ll -9nirlpen organ pipe that emits middle C (262 Hz) when the templr49l8a-: nl -zlqiq verature 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 ao . 65zzudacf- cr,r8sb s,)psnmxu85t 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 12–10 shouw4 ;w gdxgxgl2u;y) 1qld the hole be that must be uncovered to play D above middlexgg;21 xwl w q)uyg4;d C at 294 Hz?    m

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

  A particular organ pipe can resonate at 264 Hz, 440 Hz, and 616 Hz, but no(n(-( mf*6jvn zbard5 gz c3ctt at any other frequencies in between. 3 6r- nm(ncg (b(z5zjavt c*fd(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 e/o)e3k q ls-apnds. It resonates at two successlke)- /sq 3oapive harmonics 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 8 wx*i,7wecag $^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are present within the audible range for aw,f bjd8, :cos 2.14-m-long organ pipe adbfwo s j,:8c,t 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximatelyvmf( c.-8zjbal9si u7 cix7)8eu x.d o 2.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of uf z 8xi7ml7(a8 uev-. os )jcdb9ixc.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 beadzay 7 q*g h0w* uen0vitf231ot every 2.0 s when trying to adjust two strings, one of which is sounding 4407ouw 21tzin 0*0*avg3yh efdq Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz) l a/fl*qe i7 2hu17roaand $C^＃$ (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 x. 2hbh 5h wq. onujdkd,k.2;nac; cw5operates at 23.5 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 operating freq.k5u2hwj,.onad5k wn cc;d2xb. qh h;uency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuninbu(6 gm2ypx8n brk 1bnq)q .g5g fork and 9 beats/s when sounded with a u)b k(2xp5.n6bng qb1 8 gmyrq355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294q6wt5awv dp27 Hz. The tension in one string is then decreased by 2.0%. What will be the bea vwp 5w2q7d6tat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will vg*fjzn9ut) )fm +w )6hlfd2e be heard if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C zht)*m)vf2w +ul)jfd6n efg9and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B tqa5nprs2: r9, and C. Fork B has a frequency of 441 Hz; when A and B are sounded togeq25apt s9r: nrther, 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 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.:;st4d:w wqphkv +k5y A person stands 3.00 m from one speaker and 3.50 m from the :s dwy:+kph; 4v5ktwqother.
(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 brapo(sv9 uj7wh3 .dp0e vibrating at 132 Hz, but a piano tuner hears three09p vhdrojapw7u s.3( beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound of wavelengths 2.64 m and 2.76 m in air. How many beatsv0ezcik4-o e:l 4 xot* per second w zixvt- o4l4okc0e*e: ill be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire r+i2)0rz ydqpf ui4 yj * vt0ag7v4rt(engine’s siren is 1550 Hz when at res4ty vr 0rj7) tqa i42 dyigf0vp*z(+rut. What frequency 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 detewvq)dk6 + o,ux+4gdf +li k2lzct if a fire engine whose siren emits at 1550 zuv 6)l,fq2dkd+xk o++l4wi gHz moves at 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 source is movin :nctr-k79 vzkkh9r v)g toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they close? v nhc7k)kkt:r99zv-r$f'_{source\,movine}$    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 frep. k0gba0x 5spoa;ua 7quency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 H 0.7b5k oa;spxgaup0a z. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends t:1q;f6 o 6 uuk)ryd5)qcshvnout 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 receiveq;t1r6yofdc )5:6 hu vsk)uqnd sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it fk.up(.thtc 2flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected w. ( t.h2ckuftpave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on r1cwt9.twoznpf(+ r; a moving flat train car at a frequency of 75 Hz, and a second id.or wf;(9pc zt+nt1wrentical 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 measure blood-flow 288roc el xkjew,(yn oel h,47o6e,apspeeds. Suppose the device emits sound at 3.5 MHz, and the speed of soxe8 w p(c nhe4ej,6l2ko,7eyo8r, aolund in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using slf+gw fvu0l.4v*i mr)w2p q-k fzo,1ultrasonic 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 the wind velocity rj7:al6-6jsz t;3 zrtjp/w bs is 12 m/s from the nortjpj arlt-jz73/ssb z6w r;6:th, 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 o3i5-3 nvcpqb hn land 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 ati(:blq uap82ey 95c yx Mach 2.3 where the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the direc: yx5 c(uyq a8e29lipbtion 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 o3go9d6v4lc il3t cta d fs*as24)p ++wuh 9mtbf sound is httdot+93da c 9vcg)sfa+l3*iumb2ls 6 w4p4only 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 -spmq.:g/um2w-bd+ t )ixrij strikes the ocean. Determine the shock wave angle it p -i gm+xr:itmq /.pb-)jdwu2sroduces
(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 t-uq4iqec1a pyz(l 2 7$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead e.qzv30b ut zh6y.-qpand see a plane 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 distance of 2.0 km. See Fip6 yz.vh-zqq0t u3.beg. 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 downwarazw*yiqo 0u ,7 hv78b)yk/lned from the bottom of the boat, and then detects echoes. If the maximum depth for which ebhkqu znw7 7,lyvy i/ *8o0a)it is designed to 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 rflgc21zi3+wi:c epq 2k nb8 o9ange? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consnw f4;(8xrv:z) dut jkists of many pla:8wx) 4unrvj;dzt( fk stic pipes 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 mak4/f o,;c obsehes a sound close to the threshold of huma,s/ hfe;o co4bn hearing (0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant souc,y imz7g)d8ynd level when an 82-dB sound and an 87-dB sound are heard )8gz 7i,cyydm simultaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the openmu.ag mxe vh7 j4r e-macbuas4., 16l:, is 105 dB. What is the acoustic power output (r a:u6h1maujmcl4 x .s,vb-am7e4g.eW) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W outprv *dn r6:xmw*lob.. qut at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power output in r m.b*nvdlrx *o 6q:.wwatts at 15 kHz?    dB

  Workers around jet aircraft typically wear prote/k93d2hei. o bbgo rx8ctive 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 of 30 m from a jet airplane edi 38bg x9.h/r2bo eokngine?    W

  In audio and communications systems, t fy5s o379frfzhe 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 tun8rkvdf( 62 g*vwswj5/q+rknl ed 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 violc*hzo:ca0 x 6,dmg oa/in is 32 cm long between fixed points with a fundamental frequency of 440 Hz and a massgz/,a 6o :odc*0hcmxa per unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration above a vertical open tube ff4 ;z7hbgocj/k1ff p )illed 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 distan;b pg)z1fkcf4 fhj/7oce 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 t rvp6gghr ,9c14chwvsba /t*ntk(rl-2ne )/ u ube 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 thus/ 1rgvv l2cb4w r-a)/ tegnk 6p(hc*ht9,nrird harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as onewr.mjtpia e):r3x7q) 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 500–1000ov 4ys:c6di7 z-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 t7zy6 4dcios v:he 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. The conductor on thei6k31cx0: plgch9:zss(tqj f pe ,tk: stationary train hears a 3.0-Hz beat frequency when the other train approaches. Whac3h,ts0qe6kx ik1:z(s p9cl:j g :pftt is the speed of the moving train?   m/s

  The frequency of a stemnm3/( ww qwl *zylyrz2c56t,am train whistle as it approaches you is 538 Hz. After it passes you, its frequencw2n5yw,m mz /l w*r3 6zyc(qtly is measured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars just by listeni5bi0sg)qb k9x t0ai 0j5(vj4dd4 kfvwc84fllng to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the straightaway. How fast is it going? 95ijvkf0 balqjif wlb(t40 ddsv)x gk5 840c4   m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11 Hz. sb3zrmbj -2; db.e j :s5prvt3The shorter one is 2.40 m long. How long is the oth3 -2.rjb dpb;s m3sv:5ezj brter?    m

Two loudspeakers are at opposite ends of a railroad car as it moves past ipy/itq,7w8 7 hopjuu7 b80 tva 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 hearvwut/,t 8iqo 08iy h77p pju7bd 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 bloohx0hwopkph jzi 1zk4 -+a8q8 5d flow in the aorta is normally about 0.32 m/s what beat frequency0 qphzhjoxpka54-1kziw8 h+8 would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s while the moth is flying toward the bl muc;p9p4h4f at at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of tp hm4u4p9 f;lche wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series lz)*waqr1ab7 xs) nij ;01i(b fb a2ubof high frequency sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 mbax 17)w;js*1ir)(u q a2bialf nbb0zs 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 emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to senn1awduhcj(arh, gmqxki z .c ++72z gb(f 183dd signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundam,.ghzk1b i8gazcud c1+3+ (nmdj wr7x (q 2fhaental 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 of s(t0x1g7 0ntx u)yyimttanding waves,( 1n)t u0t xyx7i0tmgy which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamental frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long l 0dlcgp967myal*5 ml, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand.la9yl 5c 7lm*0lmdg6p 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 we)8(nekkg+q9: 0zq,9o5eidvw dbh c a frequency of abo:wce bv9ewn)(8,5 oqzhqdk+eg09d ki ut 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 observ s bjdmxi9h+:-br g*s0er on the ground hears the sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s ah *-i9+ 0j rgdxsm:bbsltitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 0vwgvir94x6u 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