What is the evidence that sound travels g 4/ 5md llrv;h)+1tyab*j i21y qv-d*aenjpi as a wave?

What is the evidence that socobo7(*y 15mqxw9d 3qqbub5f und is a form of energy?

Children sometimes play with a homemade “telephone” by attaching aqd pqs5l x8j:uw95 6av 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 how the sound wave travels from one cup todpq9vxu al 65w5qs: 8j the other.

When a sound wave passes from air into water, do you expect the frequency or g;h6 (5bvi8b,ugkw5 )zen kj lwavelenglg;b (hk,b8nz )j 56w 5kvgeiuth to change?

What evidence can you give tt:rrjmbo/;20m s tz o5hat the speed of sound in air does not depend signifi mb25o0om:zsjrt;rt /cantly on frequency?

The voice of a person who has inhaled helium sounds very high-pitc a fc)h1h.0nveiz x*8khed. Why?

How will the air temperature in a room affect the pid -kl+xvisp9v1jo,fa,5 aoz, qc*5p ox67udvtch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitudy6*l , yb 44xpjlrzg15a9lssa e of sounds in varijsa lp, 5r*sbg4lxl 4yz6ya91ous frequency ranges. (An example is a car muffler.)

Why are the frets on a gu;l8c.7muf yy3:- pxsn qibp;x,x2nw eitar (Fig. 12–30) spaced closer together as you move up the bulwc7;m8:xynn yeqx ,p.2 ;f 3-ipxs fingerboard toward the bridge?

A noisy truck approaches you fr. h)mvy22 jj8naky:.y8 rnj80ywecf mom behind a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound iy)yak0 jwn2rfn :e2 8y. hmc.8j8v jmys 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 “interferenceq0aj(pnp rl( )b7c/xmm)c +o l in space,” whereas beats can be said to be due to “internxam ()mjlpl( c0 cqp7b)or +/ference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered4t t4rd;dxh(g , would the points D and C (where destructive and constructive interference occur) move farther apa ;dt4th r4(dgxrt or closer together?

Traditional methods of protecting the hearing of people who work in m uo m yqnlpw-wekez7:/h-1o* a3a5q2 areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relati7:ezoaumwqhl/n w*p2eoq 3-5 k1 -yamvely 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. Each wave can be thought of as a supt6yh, nt (o:zug*le9; (+y fo n )a3elue8xkcperposition of two sound waves with slightly dif t ekz3 u8llnetonf o,)a*(ypg(x u+c;6 hy:e9ferent frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shr/ do(ewq9n1nift if the source and observer move in the same direction, with thno 9/ndwr(e1qe same velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound hearj eoo 96f ;z)dev8 2dzjd:,dwud by a person at rest with 8 v2o9fdz:jjee ;uw ddz)6,do respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of pc.q+ om hzs*q:p,vf/4ck)hj a child in motion on a swing. A monitor is blowing a ws+pckqh* ozv:qj/h , )4mcf p.histle 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 bynfx m ,lkl8uc3:y8d6t listening for the echo of her shout reflected by a cliff at the far end of the lake. She he: 3fkud8 y6cmnlxtl8 ,ars 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 ahl 6;ya1w:zkhears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the l a:haz ;1y6wkocean 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 wavelkwzkuv9.fbaqv0m b7:k7 1 kb 6engths 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 tuna on a fowqhb g2(qg )u/ggy day. Without warniq2 wghb ()/qgung, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. n87yy /kg:rp q rv.3iuThe splash it makes when striking the water below is hy83ur.prq 7 :n/y ivgkeard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stoo 1 g e*qd:)af9xixus+ aq44qbne 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: sxfa4q9*+q)qexubgdo 1a4i ? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5 on11hf sczj) lqv)f:(-second rule” for estimating the distance from a lightning strike if t: )(fvqno1 fj) 1cshzlhe temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound ajqn;x )xh/r 7st the pain level of 120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of a sound 7g c) m:is9).v krfjhdwhose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB whec)tes3 ,j49mmjcp 2r qn fired simultaneously at a certain place)rjt9mqempcjc2 ,s4 3, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally noi kd5/u05xvtj ksy jet engines is experiencing a s 55kxkvtj 0du/ound 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, en m5( lxie( .9 4dfnh4hzxpx,whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background44ehi9xx(em( nl xz.ndf5hp , noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from d.3 z4auw2j) s x,edmaa person speaking in normal conversation. Use Table 12–2. Assume the soua dm z)w.xe,43u2ds jand 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 strike onjsmt psiw;b+h;u (. yc*d)9iuxv*.bw to9*s 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 is rated at 250 W, whil(grd (icj,exu dxt*l5e3x1n .e the more modest amplifier B is rated at 40 W. (a) Estimatec(xd*l erx, ujg5ed31 (i. txn the sound level 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 in front of gb0..d (muoara loudspeakeodmg(u 0.r.a br 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 level of 2.0 dB. Wha f:lc,ise c3c7t is the ratio of the amplitudes of two esi lcf73,cc :sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is t(,niqn lr9 j,j636zpe xus-t sripled, (a) by what factor will the intensie(3u9,stnxnl zq 6pj,6j - srity increase? 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 twice the freq gr:h6jqqw5g: uency of the other.g jwqgh6: :q5r What is the ratio of their intensities?   

  What would be the sound zae6-is .git4zmjh-q (z0*o blevel (in dB) of a sound wave in air that corresponds to a displacement amplit *zih-(bs0-6 gi. taezmqojz4 ude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem ufcwg 1xj .sgb0y33,;ype1pxas loud as a 100-Hz tone that ;1,yp. xjcx 3byfuwg s1g e03phas a 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and high oy5toes /+s: xett7qhr2eh-.est frequencies that an ear can detect when the sound level is 30 dB? (See Fy soeheet7 o/.x+qhrst52 -t :ig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels.g7a;a d 0xzz/f What is the rat; az0f 7xzadg/io of highest to lowest intensity 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 lengkz6b-n, :b fe7(c/o rzv(z umvth of the vibrating port r:kz-uzn(e,mb ovfb(v6cz/ 7ion 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 lon) l/xk:h5 )q7lzfo a mglrj:q0k. kg:lld5o 7ng. What are the fundamental and first three audible overtol:o mjhof n)dl :ll.rkg 7g qzk5kqa:)7/5x0lnes if the pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant fr;f.chsslzaohb(p 3-88 box: yequency 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 t (8f-sho;axl. 3: o8hpb sycbzube?    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 spanncqs vo9l87,ws/plr2kz x, g/d ing the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of piw7scrx2 k9 zdp,8l svo /,q/lgpes 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 will:rvt -apl m9gxx l40ls( qnd/a6km,j / be its fundamental frequency if it is fingelrksx t(-:pxa jdl6 /4qg a0nm9/ ,vmlred at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned t6huh -0 tr)y5y lynnzib/1d; no play E above middle C (330 d1il/nur 6;y0y z h)ynt-h5b nHz).
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that emits nsh, myd2i/9m cz3r*hmiddle C (262 Hz) when the temperature is 2hnm,39d 2mcr iy* /szh1 $^{\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 2065 gg )y2x v-g9qhesfgu)s /7orx+ofj $^{\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 qsej wp87xo,3 zl/b4y the hole be that must be uncovered to playzw/8yj 7os 3epl,x4q b D above middle C at 294 Hz?    m

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

  A particular organ pipe can resonate at 2dp8),eomy j6i64 Hz, 440 Hz, and 616 Hz, but not at any other frequpy 68j d,mie)oencies in between. (a) Show why this is an open or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at both ends. It resonates at twz1;e+xx q4 dipo successive harmonics of frequencies 275 qix dp; 4zex1+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 w 4a7v4ybbk dd hm79i5$^{\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 aus 7aqgp6 reo p)l)n;,fdible range for a 2.14-m-long organ pi)fpn7 p; e),s6aqrol gpe 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 outsebb:o;2a (ieg ide 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;eg:b2e ia o(b is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to adjust two stri;)m0bmo c02 sv ha 9uj3ernrin74 wt)kngs, one of which is sounding 440 Hz. How far off in frequency is the othv)nr0 )mk0o w23mr9 ecb j7iatus h;n4er string? ±    Hz

  What is the beat frequency iyd2+p8yb p+pxo. af .wf 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 operateo/m.zv;k i5zpq1 1v zrs 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 frequenzi 5mzp.v/r1;o1kv qzcy of brand X.    kHz

  A guitar string produk ady za5 6ujf,0)m5nkces 4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz j adf65k)au,mz0 yn5ktuning 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 tbe20ypw ;b)vo ension in one string is then decreased by 2.0%. What will be the beat frequency heard when the t ;2 obwebpv)y0wo strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if twoupgg/ nr0vu.) identical flutes each try to play middle C (262 Hz), but on/ u .gp)0vngrue is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, Bqz a43hzr;ue), and C. Fork B 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 together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are p4e 3;hq )urzazossible 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 s1u(d 3upz;dh 7zkt2.okfqg b5bjq3-one speaker and 3.50 m from the other.3 ;dtq sdq5zub.2gko-j1b zhp (ku7f3
(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 supposbyzx qh*y4we6v;-;2uif6:pr t /ppte ed 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 vibrating at 132 Hz, what must be the frequency 4vuyxy6pt; 2*ppf rwtz;e:-b e6/qhiof 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 beatsdqvgy.b)c d 7tg.; pfkx26t,e per second .g .y76egtdp)t xdqvf bk,2 ;cwill be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency omi ( *)tdy0gigf a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a spee0ty) * gimdgi(d of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a fire engine whos8czeq s0o 2d*ve siren emits at 1550 Hz moves at a speed of 32 m/s d0ozesq2 8*c v
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz so nh: m1j/wqgdwh8i7t z.i3 2xpurce is moving toward you at 15 m/s versus you moving toward i 2dw1xtq 3ign:/zhm.pw i8jh7t 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 w2,gb3egwgq 5f4m5 6 et m*qdgqith the same single frequency 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 Hz. What is th mq qf43gbetgmd5e52,g6 qw*ge frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

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  A bat flies toward a wall a.fepg ef2e5*r;n/ ) aemok2lrt a speed of 5 m/s As it flies, the bat emits an ultrasof rf2le /2n mr5agpee. e;*k)onic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the originalkiqqln- 89 7hqrfi5t 8 Doppler experiments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone while at rest in the railway station. ni85kh8qt9 -l q rqif7What 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 speeds. *) / vz zl8wyjv.jjhf: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 t)* v j:flwj8/vy.hzzjhe expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of frequency (h6 +d(;yv w8hppf pya $2.25 \times10^{ 6}$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. Whenq l/h 6n-v7ww0 -myxgr the wind velocity is 12 m/vhrmxy -g0 7/ wl6nw-qs from the north, what frequency will observers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on 77gc g*fstlz5hj6c: tland if its speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where)gl8:cklf c +zvf6o/ w the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of the airplane’s moticf:l6l+f c8o v)wz/ gkon?    $^{\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 pla:qgbqyfda j g b(,ew4r86 6a8xnet where the speed of sound is only about 35 m/aa e48xrgd b86, :fqw g(q6jbys
(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 wa pvl 1+pm3n-ckvf+hp8hpm/ 0hr*q f9ive angle it pr3pvlq0npf kp1hp98- i+h fh/*+c vmmroduces
(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 l8dj t 1jrr/t.$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a plane exc je z3m(i+iukln u279actly 1.5 km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane2imlk(i 9 +ucn7ju z3e 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, jl4;rf-f :48cbtcypl-ppofe s7*rp sends 20,000-Hz sound pulses downward from the bottom of the boplo:p4ye ,rtf*c;jfbrfpc7-8- s4 lpat, and then detects echoes. If the maximum depth for which it is designed to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human au z6 o3ocft7qsm2ww0s:dible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display 9r+hl fndc, wqyj.inh q,s1p0 36tz+bcalled a sewer pipe symphony. It consists of many plastic pipes of various lengths, which are oybcdjznnwh pt h3f li+q19, .+rs 0,6qpen 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 sou2llncn90ozv ,p gg c:cfgjoz wzr .29k6,w6z-nd close to the threshold of human hearing (0 dB).lvc- lwcgg92n.rgzkno,zz,6f0 p: w o962 c zj What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB soun 0y hg4e3sxdhvb16y4ed and an 87-dB sound are heard simu4b43g0e6 ydehv h y1xsltaneously?    dB

  The sound level 12.0 m from a lo *v2i e2a hnyamfg.1(cudspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the speaker, assuming it radiates equallyf 2mc(.aivahg en2 *1y in all directions?    W

  A stereo amplifier is rated at 150cdnz9o55/:knl q; gbx W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power outp/n;55d goxnkq :z b9clut in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devic r0u00ga83 4uu.2g hixuqr nbees 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 airplane4ue rrxguuqu.na80b3h i0g02 engine?    W

  In audio and communications systems, the1ppp hzr.i34h. qq z5zh*en :9xk7d dq gain, $\beta$ in decibels is defined as
$\beta$ = 10log($\frac{P_{out}}{P_{in}}$)
where $P_{in}$ is the power input to the system and $P_{out}$ is the power output. A particular stereo amplifier puts out 100 W of power for an input of 1 mW. What is its gain in dB?   dB

  Each string on a violin is tuned to a frequency 1omo.vua dre7f .z 5g(mp+3kx he c*g,:$\frac{1}{2}$ 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 *ajyf. wr-o/b81eao yis 32 cm long between fixed points with a fundamental frequency of * o-afyw1./8bjoyera 440 Hz and a mass per unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration above a vertical open tube 6 j qvh*p)a5fo *xjos(filled with water (Fig. 12–35). The water level is allowed to drop slowly(aq x sp*ovj*jh5)f6o. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of mass 2.10 g is near a tube that is open at m kd*kip71 o9jf 4: h3)repi2dr hmk-beo ;j7rone end and also 75 cm long. How much tension should be in the string if it is to produce reson2f4o h-j ddr7i;1e7:ok*rb3hp rpjemk) 9kimance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resi6 n-v*l-tk6jasiyj * onate as one full loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz range coming from two sources. T*e -8k 7 )hlqmbgorn +l6-jmbdhe sound is loudest at points equidistant from the two sources. To determine exactly what the frequencg)l m+-oj8h d q6e7b* -blnrmky 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 whistles. One train is stationary. The conductorzo9 vvc w,mpg .(q0d;n on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. Whang9v0(wozq dc, ;.vm pt is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approaches you is 538 Hz. Afterqlqs fwn trt 4944ea*- it passes you, its frequency is measured as 486aqq 9* t4-e4 4trnsflw Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars just by listening w x(64)spkswpto 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.ws 4kws px6p)( How fast is it going?    m/s

  Two open organ pipes, sounding together, prodm.pta/f0nd 3duce a beat frequency of 11 Hz. The shorter one in3/ a.p0ddft ms 2.40 m long. How long is the other?    m

Two loudspeakers are at oppos ifi.zqc abc1h4/(4 zsite ends of a railroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 124hi/ .cbq1sz fz (iac4–37. 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 abo d.p 7kcax.y jh20d)itut 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow hya07.cp)x itdk.2dj 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 k l4nddsqa:gn.w09 6his 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 detectehq0469skw l: nagdn .dd by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequeny5neo 7iy+;v ;hj ldw)/;sa zocy sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp retun wzjoih;dyl; sa;5 vo7y/+)erns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used tov8k 5 j7e.cdf;yl5 ied send signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundamental frequency of this horn7vd5dfie lk8jy5e.c;, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo liste.;8.-hpao:j*o t zeg+u mx af(zf(njening can be compromised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamentalm;anjh.e+8toj(ozx *f.:- p a(fgzeu frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, ca4-f:moz99ry cd -q aetlled “singing rods,” involves a long, slender aluminum 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, z fa te4qydcom9--r9: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 o1lb20qgyi jn3f about 1000 H qnb yj0lg2i31z 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 oi8c fd.yrj :pv78x/*xf;x:q e( rma las6t3ak bserver on the ground hears the sonic boom 1.5 min after the plane passes directly overhead. What is thfd:r6t.a8r3k axm/cx 7jve8* flpxyqs(:;ia e plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat isih+p82miz,ok 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