What is the evidence that sollv.z .gx8qby x u 9*p.r-o;rompy1- bund travels as a wave?

What is the evidence tpzd 6;1 vfyx-qhat sound is a form of energy?

Children sometimes play with a homem,+ccb0n get7siek p- ,ade “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 cln-0sb+ ctepe, gkic7, early how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you expect the frequency10sjjh42q25k4 q yn e:x;c)aayruxji or wavel4nry)h;c axa0j eu 41kjy j5six q:q22ength to change?

What evidence can you give that the speed of sound ,ni /d xloinj5uls :40in air does not depend significantly jsoi: nui4lnx,0d5/l on frequency?

The voice of a person who has inhaled helium sound8+bqaasm3n k. na0 4cts very high-pitched. Why?

How will the air temperature in nfa 7vqo +o4d(a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude of soundshidj,dhbl / w a/d8;bgqs( f(: in various frequencb,djh(;/d/ a:q(b 8hlsg iw fdy ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as y crv.jfi 6t36bou move up the fr c3v66ib .fjtingerboard toward the bridge?

A noisy truck approapcyc7zl / ue+5ches you from behind 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:cc+z e 7/upyl5 See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in spal47 u8k- .xhwxi:p xuyce,” whereas beats can be said to be due to “interfer hxk-7. xwpy:84luxuience in time.” Explain.

In Fig. 12–16, if the frequency of the speakers we xqs)1t wr+-6*/f (vwzebrbtgre lowered, would the points D an6q)* xvew zrg fr1(-bt bw/+tsd C (where destructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who work in areqiqy4xv ,o1iq7m*bv i *u(mh.as 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 the headphones in addition to the ambient noise. How uo(4bmhqqii.y *7i*m,x1q v vcould adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought ozmebons:.dsl,6 an06a 5 hyr)vp2 m4 qf 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 apart? Explbam2 zn dsoq.,n:0r4hpse)lm v65ya6ain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observi11ih,uze)h 5ljg z t7er move in the same direction, with the same velocity? Explaih51tgeh)z,jiiu l z17 n.

If a wind is blowing, will this alter the frequency of the sound heard by a pe 6 gje1zoxwwq242fhz;i9g6q jrson at rest with respect to the source? Is the wavelength or velocity changed?g4 o;16i 2z2q hx6ww qzgfej9j

Figure 12–32 shows various positions of a child in motion on a swing. A mu ah x7i3.ezwm/s.o*jonitor 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 fo sju h/3m.7x .aeio*zwr the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listenin89v /2*1 frkz hz dbaa:q0uizq 0oc,aog for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after sho z fr9kz10 *b0a82/ q,:ooidaqvzuachuting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He hears the 6mmjcj+nelnt08 r /2czw (c4iecho of the sound reflected from the ocean floor directly below 2.5 s later. How deep is twc6 etnz(m+84j/i lc0nrc2m jhe 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 wavelengthcn9u bcjpj;)vl/ ;3f zs 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 foggy day. *cei,i 1 fis/bWith1, ies/ cfiib*out 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) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splastuzolwxt bs d w;qx 69(d++q()h it makes when striking the water below is heard 3.5 bd +tol (9wsx)uzd;wxq+( q6ts later. How high is the cliff?    m

  A person, with his ear to the gros1h t6+aw6,0poox1q-qwzt smund, sees a huge stone strike the concrete pavement. A mome o1qt-wt+6o1 pssh a,x0q6mz wnt 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? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent e0k8 ga,2;cxb2s nn:uunuu. ohrror made over one mile of distance by the “5-second rule”x:un;s2n,.uc8akbn2 h0 uogu for estimating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a souneh1x;7yvpq n q.ln;-y d at 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 n4 +ez 71 4ijj;odjlrv.t6icqof a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers prgadqx6i)ls5 mh6ypn 18 4wi m0oduce a sound level of 95 dB when fired simultaneously at a certain place, what will be the sound level1a)yhwi m8dxiq nslpm6 50g6 4 if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane 6 eer//qibah )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 q)habr6 / iee/down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have (zb2( kyqp )yka signal-to-noise ratio of 58 dB, whereas for a CD pp((ykq) kbyz2 layer it is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speakixel/f(lo ztc,. n wi3* m:jz:ung in normal conversation.i3j: o,*.(nxc/: w umetzf zll Use 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 eardruyah r5ky,eud j 69v(4vm 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 ratedg znnh-ehmmdjgn/e6u,9)l )ol5112wh ypf 9b at 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels y9 emnl29/d6 -)ngpbu5lh),m fy h1zwgo1enhjou 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 1f(ypilb +k(j 8p 7-ehdspd45r30 dB when placed 2.8 m in front of a loudspeaker on thebh+sfdrl7p d( ipe4k j8-yp (5 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 typ+cz bhlk,1f6e ically detect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by t1cb6 ,hke zl+fhis amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the inte nq1qbflb055 em*1wihz.ga) n nsity inn ql wabgi5 hbe5zq.f)*n11m 0crease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have eq :lv :n /wton;lfx3 6axu*fv8an2-prqual displacement amplitudes, but one has twice the frequen*vlln t:xuxa:f;f6 /r v w2n8ap-oq3 ncy of the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of -xvjhw km om+d (t5;d-a sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 k+dtdhmojm ;-5 vw(x-mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tone thatv lyc:q6su4 b3 has a 5u6:q34c yl vbs0-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect whm5j uh8 yie/ru9 f0s74 3wahjlen the sound lej30ihuej798wl h 4myus/ar f5vel is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound +zd8arto c7u*h fz9jgi 8 3k,qlevels. What is the ratiohk+3 odriz,8 z c j7*a8ugqt9f 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 freque lbii/zzur9 e,iy,tu: d(1l;d ncy of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the slzul,ziii1d; e:b y r /tdu9(,tring be placed?    N

  An organ pipe is 112 cm long. Wh;yu jo cev7v; 99*lekcat are the fundamental and first three audible overton;cv l 7uyv;oe9k*9jcees if the pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you expect from blowing across the top ofx 0beyg jp/ h:9b1a2cq an empty soda bottle that is 18 cm deep, if you as 9byhex0cp 1/:q2 agbjsumed 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-tube pipes u eiy mz.5*)gmspanning the range of human hearing (20 Hz to 20 kHz), what would b i gum.yz5e)m*e the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a fs)i+xgo ( mty*requency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its original m +si*)(yxtog length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play52b2 j mw,gn-jyiuqm0 E above middle C u2-0gjm ,2qybin5jw m(330 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 that emits middle C (262 Hz) w+vx434od hv xf7 2czkzz.di l5hen the temperx z2fi d+.c4 4xvkv5d3zoh7zlature 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 r k b ,;m ogzyffz,qy3:8xqt71at 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthuh fr(u3) a/sipiece of the flute in Example 12–10 should the hole be that musah u)s3(ri uf/t be uncovered to play D above middle C at 294 Hz?    m

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

  A particular organ pipe can resonasl8c:6p7q,w m dyn(zf te at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show ym(l8n6: zw sc,dfpq7why 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 reso2:/ bdtq3p, ynss qtj u8*p0cqnates at two successive harmonics of frequencies 275 Hz ay:/qt u st pbdc3nqp2*s80jq ,nd 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 jsgzo o2y 38;v;h y5vzabf5 p;$^{\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 rar- ub;1n*1rw7wn srktnge for a 2.14-m-long organ pt rr1n1ubn7*ww- sr; kipe 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 owi(h48frv (v outside and is clvfrh 8(v4o( iwosed 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. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when tryir2 *n too g8nycf72vc9ng to adjust two strings, one of whicrctf*9nn722 c yog8v oh is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz)aj j*pk. n +kb*nnt0c9 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, wf,9 z ltk:4kgshile another (brand X) operates at an unknown frequency. If neither whistle can bzk4lkft9 s,:g e heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning forkbh)(v4upkcljem xk *zwqa :y4t -),e)vev2j 8 and 9 beats/s when sounded with a 355-Hz tuni q4j4eczhew*)uyp8vek:bavj-vtkm2 (, )x l )ng fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the sam(z wj0f+o ksx0e frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat+(oxwsf0jk 0z 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 each try to play middle nolldw +.y45/d w,wj+vjkdc.C (262/w,j.5jdwd vlwdcy+ . o4n+lk Hz), but 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. kbv6 :z+xyb *yFork B has a frequency of 441 Hz; when A and B are sounde*b :6yyb+v zkxd 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 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 ancdmx;(c teb 5-d 3.50 m (tdx5c-m;bec 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 supposed to be vibrating at 132 Hz, + ) iidn7 5wc;c:w1l ito9yxjnbut a piano tuner hears three beats every 2.0 wi5nljc+y i 9w) ico;tx:n1d7 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 man -2gvlg9qrk s/y beats per second will be heard? (Assume T =s- / rvqlgk92g 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz wy(:)jwgqzr.9p)ch cq n av3 hg 1-rzk8hen at rest. What frequency do you detect if you move with a spejrp9cnk-q(.zhgz )q3w cy:8r 1va)ghed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing stilylg qv55w-u;m l. What frequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of5v gmwu5;y- lq 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving towdj0p iv .:qyf6ard you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they 0p vdj6fiq :y.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 equipri5s1:q.jvmo6q prh)ped with the same single frequency horn. When one is at rest arj6:mv5ih. s rq qo)1pnd 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 the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves atp4 fci okq; 3qnc*p2)ypaq5 2t 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s4p3ckqf 2o;pq25a*ny)pic t q What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat emits an ult:xz+oym w )xbj+foba z,vn+) wp nu;,+x8ebp(rasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear aozzwn fpm(v n;,x+ b+p)x, be+:o+j w8x y)ubin the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was pl5kd73k 7;rdw(hz(vgj r+hp vj ayed 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. What beat frequency was heard if the train car approached the station at a speed ofj kp7rdzvd( (v5;h 7rh 3jg+wk 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speed y )g:spafar3g z4f/4hs. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is tak4 a hf/:gygf)r a34zpsen 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 uc,, g:b 4g /)kq,*fczcng gcu .*pnwl;xum0gvltrasonic 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. km cox9s2a)y ,/st9v3( pqmsj.seqv, When the wind velocity is 12 m/s from the north, what frequency will observerq,sy,ajv9 kqv9/pmc s t.2)mx(eo3ss s hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if its spee.1t:fmb spy9lps* *nv d 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 Machkze7, dzjqjbvh -9g+ 6 2.3 where the speed of sound is 310 m/s (a) What is the jg qzkj 6dvz h-+9b,7eangle the shock wave makes with the direction of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmosphere of a /uc+:uc cdsnbpgy juo18u2. 1,ry nwe (e7s/nplanet where the speed of sound is only about 35 m/s uc1urwnnc71 8snu :+/ y /ug,.ys2jb dep e(oc
(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 tdx:2,j:ii 54(d mqtzmz bzp;rhe shock wave angle it produceqbzm z(j:p t:4miz5d x2i;d, rs
(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 juf in)1)3myf$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a plane exactly 1.5 km4p- ob266vkqqlgvjf, v,i +(kpln hh: 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 Fig. 12–34. Dihv(+,l4o:p6vp vf,gqk2jh-nk q bl 6etermine
(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 tcmk9(x/n; 5i 818ge;ci/cdtr hszv ssends 20,000-Hz sound pulses downward from the bottrs8de x /cti;9k cn5 1c8h(z/g;itsvmom of the boat, 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 th :6dc ;ndrg+ sih;iv2de human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pip +;9gk3vt2m +q f(hjd9e/gb+ vvmiib ge symphony. It consists of many plastic pipes of various lenhb vgg qev(ikdbt+m3 29ig;/ ++vj9 fmgths, 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 threshold7102romsydyi 4 xl/ zd of human hearing (0 dB). What will be the sound level of 1000 such mosquito romdis0ldz1yy2 x/47es?    dB

  What is the resultant sound level when an 82-dB sound and an 87-dB sound are h1 b33t)umpd /1y0pavzll( xh ieard simultaneolmxa z1dbp/1 p3) thvi03(uy lusly?    dB

  The sound level 12.0 m from a loudspeaker z )e3.:os)z ad47vx-amlnbyb , placed in the open, is 105 dB. What is the acoustic power output (W) of the speaker, .ev4dn xa7z3 ozbby-)l):asmassuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The power output drops b9fhd12/xl*z *v*rmqmiy qw y0y 10 dB at 15 kHz. What is the powqy fm lw/zqyrdv 0m2*1i9hx** er output in watts at 15 kHz?    dB

  Workers around jet aircraft typiov4z ;.xvax+yg0o x 47srckq7+t l. qqcally wear protective devices over their ears. Assume that the sound level of a jet airplane engine, at a distance 4t7q x;ksgvxz 0co7q++4a r.lx.yoqvof 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 engine?    W

  In audio and communi k6qx-vv78 1e;b-s zxn2o7jule b0rf fcations systems, the gain, $\beta$ in decibels is defined as
$\beta$ = 10log($\frac{P_{out}}{P_{in}}$)
where $P_{in}$ is the power input to the system and $P_{out}$ is the power output. A particular stereo amplifier puts out 100 W of power for an input of 1 mW. What is its gain in dB?   dB

  Each string on a violin is tuned to a freq4jzu 9 -e1tw6bz6xjltuency 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 viol20djq0 30qn 8 l9 iyyufnw/iciin is 32 cm long between fixed points with a fundamental frequency of 440 Hz and a mass per unit lengthiy uj l0ii/wcq8f00q nnd9y32 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 ab7ugdhq y)3-4vq, bet uove 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 re,-beu7d hv3tuy) qqg 4sonate 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 m s(g cid*m(( (n2eqo yh.id2iwass 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 sqw d.cgm ii(2((nh2( idy*eostring if it is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed k (lrsu:gpd7ec/l6q 1ayn v/ 3to resonate as one full loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 501bcr)29t y-fh zwiw gw) hc6p)0–1000-Hz range coming from two sources. The sound is loudest at points equidistant from the two sources. To d 1)hc)t -2hzw9rf ypwbwi6)c getermine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationab z e ov )ztfib(j5u)/gfm4n::i6ox.r ry. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the spemz:o ruevt 5).4)/o n: bxb(fgjz6ii fed of the moving train?   m/s

  The frequency of a steam train whistle as it app ubbyo jo1ie/lz o2a,zf,+* )oroaches you is 538 Hz. After it passes you, itsazi+ lz2oo ,,*bbo1y ue f)jo/ frequency is measured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estim fa3r mwj,lh1) e7:mdiate the speed of cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sounhr,m) 7dm3 ea wf:l1jid of a certain 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 frequency of 11 Hz. xswf2)( 16gmm xprdw9 The shorter x9p(dwwr6)2sgx 1fmm one is 2.40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of a 3mxya96eo -1rgtz n7 gs2rn8trailroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listens from the position A, in front of the car, (b)gt7s8ytg9z - rrxnea 6om21n3 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 az aqsd)/jfmi 0 *b1ad(orta is normally about 0.32 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? Assume tmdi(q db0aza*f 1 )/sjhat 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 ftb 9* ::zn( ji)qxh u0jics2bmbu5:wblying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the fre9j :u (iu t5w)*0ch2b: i:jbzmxsbnbqquency of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound pulses as it apprtbml, r 90nl+coaches a moth. The pulses are approxima0m,b9 ltlnc r+tely 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signals from one Alpicbj ,2l 44t6v)ozc omyne 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 alpe 4 bc2jotlom6, )4vcyznhorn 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 horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listenkida43rdzb) : fz- 4aying can be compromised by the presence of standing waves, which can cause acoustic “d aa)4z-f3ydi4 kdbrz :ead 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/c z6y )h,:- ewdihajg 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 littlewzha- :/,d jh6g)ecyi 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 t a(j0xja)na)u 5hhb)ko *vf o.he human ear at a frequency of about 1u0ov k5. a)jnjha()*) hoafxb000 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 thetj dm9b3lz k )q9wio+5 ground hears the sonic boom 1.5 min aftiqjldw99b)o+3z m5k ter the plane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboaso m(jxtqa9j68r8z2-.uot v xt is 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