What is the evidence th4 pkq:shx jpn4cv//) hat sound travels as a wave?

What is the evidence that sound is a form of eky,o 3o4 t rnp) ly.gatf d2sv.br7q e98y7)ignergy?

Children sometimes play with a homemade “telephone” fo ezo udc::.mm0 ) :.upous,zby attaching a string to the bottoms of two paper cupso:.sc.uu dz:, :f0 pmm) oozue. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you expes8;w1 iz,9dfrur9x9 obt6kapct the frequency or wavel d1996asxp9; 8rt,r iuozbwkfength to change?

What evidence can you give that the speed of sound in air does(onis sdm7yk z8 4.c6t not depend significantly on fr(y6n .4d 8moss7ctikz equency?

The voice of a person who has inhaled helium souwqg+/h ; sv1y(q*ydohnds very high-pitched. Why?

How will the air temperature in a room8 s z f:j6: o;jacideqw),wl6z5q imi0 affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude of sound6eg xddc8nj7: s in various frequency 76dcx:8e gdjnranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you move a g/:w.ifh9xo up the fingerboard toward f9i:x/awho .g the bridge?

A noisy truck approaches you fp8ssoro rglk- p.3wark-73 0trom 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. Explainwp7a.sor3r 0s-klrkg3 8- tpo . [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “intki8; 1 i0n vp.wkprq7merference in space,” whereas beats can be said to be due to “interfe;.wi 7pi80v rk nqpkm1rence in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would thc pc(x+ g*1rfge points D and C (where destructive and constructive x1g+ccrpg( *finterference occur) move farther apart or closer together?

Traditional methods o0uf;4q o w zlao7b*tq:u ,c;onf protecting the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the am 07lu;4,: tuo n*bf;woacoqq zbient 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 though 4 9gk*ydz/.2gwzktd it of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In whicgw 2*yzd9.tkg/i4 zd kh 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 move in the same dirsde wb;90j0*: j5k ikyhvsdo9ection, ;ybwjjd:i d 9vk5*seh00 k9oswith the same velocity? Explain.

If a wind is blowing, will th9q (ygcyb)j )jx. wj;pis alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength o)ywj) pj;9.gy (xqcbj r velocity changed?

Figure 12–32 shows various positions of a chidw9/*dr se7eald 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 freqa/s dw*e 97dreuency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening dq5x5(6 jtd2gd yx4si 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 shouting. Estimate the length of the lake. gjx(d6di524yx5dq ts $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship ju -whd ea:ddi4m)c/s6 gst below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does no4i cgddm6sae :-hw/d )t vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air a63n l ddjnqni509icx 33.xcltt 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 .hww *re08u5 k5mlx ktbvf0)ftyg3 p+ just above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time el 8 y mxbe0v*k 5w)5wtlrk0fp u+gt.fh3apses 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 splash it mao- b2s/h 3h: bfyrel9fkes when striking the water below is heard 3.5 s later. How high is the 93fr2h/-lysohb :b fe cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the concrvi ,1kdv+uoi(,(m 9vvait 5hy ete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other ivvi, 9vi1 o (hamkuyd,v5+ it(n the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-second rdqo;jsm3 6+kodt )ax+- i0bd wule” for estimating the distance from a lightning strike if the temperature is (a)0-i s;+kx6bo+otaqjd3 d mwd ) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level or28 /x4wucjdpf 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 whose in d k,rof(fer :j/b9bq,ku,d:dtensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level5;wj 12 voyq/ zwv,okhisd:9a of 95 dB when fired simultaneously at a certain place, what will be the soundok ai2w9oh;s z,5 qwj vv:/1dy level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four eqak;cwht b0b 1/;rrazjo *4aa /ually noisy jet engines is experiencing a sound level bordering on pain, 120 dB. W raw40 1;aj/bzc r a*ta;k/bohhat sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas f 6g6r2k/ owmwgor a CD player it is 95 dB. What is the ratio of intensities ofg26kmw r /og6w the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output o4adc huor24fq9gr9 f a ..)joof sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere ceo rq )9r49aoo hc.f 2ujadg.f4ntered 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 strikqfgmd aszl ))q2)ru+7es 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 9x)4yq je)yjd W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decjy x) d)ej4q9yibels 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 pme:gfme 1q:0mhr i9*d-wle4 blaced 2.8 m in front of a loudspeaker on tqm rg1*-ibf9e 4dh:wmeem0: l he 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 dBr uqqq(8s+ xu(. What is qu 8(qsu( xrq+the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sbgk 64wmfm+4;6gelz v ound wave is tripled, (a) by what factor will the intensity incr6 kv4b46mge;gml fz+wease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal rb7 l+i)vcxy2 be.q.+p( dhgr displacement amplitudes, but one has twice the frequency of the other. What is the ratio of the( ).2+e+i. rcpqd7bxhr bglyvir intensities?   

  What would be the sound level (in dB) of a sound wajevqa 60ofa51bnt,u 6ve in air that corresponds to a displacement amplitude of vibrating air molecules of 0f65,ab16av uqeo j 0tn.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tone t ynqkh xmr9l18;b6f82nyn(ez hat has a 50-dB sound level? nm81nqxr fbz;lh8k y9n6y2e ( (See Fig. 12–6.)    dB

What are the lowest and highest frsomi;e3p3feza q1 -h:equencies that an ear can detect when the sound:;po 3amz3i1-qehe fs level is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is the rj+ - f)ebn(amrg;v .h jfq(5vzatio of hihv;(f )an(jr m -bfqvgez. +j5ghest 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 vio kwr m+ h73im5 0 jkvrf6p7ibo.oma/f-lin has a fundamental frequency of 440 Hz. The length of the vibrating portion -k76ioomrf h7par.3kv0b+w5mf m/ji 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 are the fundamental and t6j epv1b; s2efirst three audible overtones if these1 b2jvtp; 6e 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 blowing6gq.ze ly;z8su+ y9 fi across the top of an empty soda bottle that is 18 cm deep, if you assumed it;89izugzef.sl qy+6y was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a7g j*ul sdb,3r pipe organ with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the *3ujb r7,d glsrange of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has:taxy icf;, ,1ae0qgp 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 its originaq fap,0:1 ,ct;yigxeal length?   Hz

  An unfingered guitar string is 0.73 m long and is tuneta9nu)kh uv)y*ms . t8d to play E above middle C (330 Hz))8ut s h a)*n.ktum9yv.
(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 sz(jj +gn-:16 t qgehzok, 0h acfo/+yorgan pipe that emits middle C (262 Hz) when the temperature +/kgt ocjso 1:a-f zhy h0g+q6z j,e(nis 21 $^{\circ} $ C.    m
(b) What are the wavelength and frequency of the fundamental standing wave in the tube?    Hz    m
(c) What are $\lambda$ and $f$in the traveling sound wave produced in the outside air?    Hz    m

  An organ is in tune at :ohgcal9,bp; 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 should em5 bz0., sofy4bi*l s2v.d rkck5w:ethe hole be that must be uncovered ty *bilm,e0 o fsz.vd 5 ks.kbwr5:42ceo 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 resonate at 264 Hz, 440 Hz, and 616bl31vei yj43v Hz, but not at any other frequencies in between. (a) Show why this is an open o3 4yb1vlei 3vjr 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 boqn.-yjco4 p,ed tys6) asep2. th ends. It resonates at two successivey-4apt .oecspy2)s.6q ed , jn 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 39nc xqa/;kd sls;st9$^{\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 a 2.14-m-long organ7r6katu-qd f2 pipe at -6tdfa2 kr7q u20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is a 0vqsmu e5+7.*tboistq ,v:ut z .tzd2pproximately 2.5 cm long. It is open to the outside and is closed at the i z*tv7t u e.z,2v+tbusq:5otq m.s0dother 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 ac2l0nx-5 :fxhjpv3i when trying to adjust two strings, one of which is soun0pj2 ih-ca: 3fv5xn lxding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat fre(p*yxwpn 25/*dlpst w pc -a9v12nufwquency if middle C (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, whilq2(h.1:3w3 lr t1a wbd hqmubhe another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but am ww23.ht1bqul h ba:hrq3(d1 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 tunin qb v7e6go; owg*j(oy)g fork and 9 beats/s when sounded b; jo(e*y)ogov76 qgw with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension in onemnnwzz*4* 1n)2 wyo s.p niae1 string is then decreased by 2.0%. What will be the b.ysmw2)nn 4w**1znozn peai 1eat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two i1g 6jbaru6 jm;,mx) nr1kwq:xdentical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the otheq)r 6g:bxjx6,n;1m a u1jwkmrr at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forp lg; o,zsv0d6ks, A, B, 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 ardopzlv0;s , 6ge 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 apbvihp4n;9 2 kmgf ms62 sk56ynd 3.50 m from f6kby69pi k 2;vmm sn45ph g2sthe other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are s:( 4 +znukhcodupposed 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 Hcd k:z4 n+o(huz, 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 tkk z*7:x2oco of wavelengths 2.64 m and 2.76 m in air. How many beats per second will be he2 *7koktxzc o:ard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz when at rspjkfi-/h4* rest. What frequency do you detect if you move with a s fjk/-hpi sr4*peed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What,*udkvej 4 qh89 fzp5j frequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a sdhu9 85*pjkvq fzj,e4peed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frzna:29xnsc /i na c7(nj5 z*dnequency if a 2000-Hz source is moving 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? nzi (/d:7 nnxz2accnns 95*aj$f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with the same single frequency horn. When onav/(l mg4 )s il8iv(wte 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 the frequency the horns emit? Assl)lw 8/a(ms4v(giv itume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and b 3/+teuxu eexfbf( 0k8*uis9 receives them returned from an object moving directly away from it at 25 m/s What is the rec/0(stfb8i 9 x+e fu*3buex kueeived 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 ula g isxm(8//j g-e (7ns6ietc.*zdth otrasonic sound wave with frequency 30.0 kHz. What frequency does the bat 7oije/sd(gz. -g nc(ea shm8t6/ ixt*hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving flat t 2tm0mzpo9ds 9rain car at a frequency of 75 Hz, amodt29s9mp 0 znd a second identical tuba played the same tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves fiz m y9n*m,i-to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the s ynz,9-imm if*ound source?   Hz

  The Doppler effect using ultrason tzgb1llo /p.9ic 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 is 12 hc10mu6hw u i9+a.c0pgwni9 u m/s fromig90uh hcw+a.9n0p 1uu6w mi c 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 land if itfp04cdqr g dh85r0,an s 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 tey 04tdt 7w/pzuq fb457 os;ut/ :mpzjhe speed of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of the airplane’s moz40;4o /f dtpstjp /7q tm u7:e5bwyzution?    $^{\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 wh46a ;-r fdb0xdzudc)yere the speed of sound is only ab6b rz-);y40 dcfddax uout 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s strikes the ocean. Determine the shockdzz4 73 p; itw.x-ioml wave angle 7-3z ;o p.ti izlx4dmwit produces
(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 , cplq, zll aug3 (5tllm73w(w$/theta$ 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 1qkrh4nb tr ,idvh 0fu*3ah:f,n owf7e,,u-f7.5 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. S,74iq3d rrf,khtnwuf a0fb7h h on*,,vf- ue:ee 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 deva mfd--or/7hg ice that sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the -a7g/f-m odh rmaximum 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 b iygmaz 6m bf75z7ny juyf-. 15jq9r(human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe sympfm bkbqtx(,jd1i* l)4hony. It consists of many plastic pipes of various lengths, which are open on b)dl1j , mq(i ktx*4bbfoth 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 lrt4fz aqy)x)ni4 2- rsound close to the threshold of human hearing (0 dB). What will be the sound le f-a)24 rn)ri4qltxyzvel of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-d ox4b1yb :48vwl8ze bhB sound and an 87-dB sound are heard si48 o4l8zvh1 ewbbxb:y multaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 ddy*qaw px;kdz9 9b1)yj9x tu/B. What is the acoustic power output (W) of the speaker, assum9;* 9awpzyxkuytq db1xj)d/ 9ing it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1* drg 1vrn7;py000 Hz. The power output drops by 10 dB at 15 kHz. What is the power r*ydgprn7v1; output in watts at 15 kHz?    dB

  Workers around jet aircraft typicallq*a dd5 xiy. bjy+ 7xjviomfhk9 74; g)9kaf7ty wear protective devices over their ears. Assume that the sound level of a jet airp57 ji+)qxtof 9k74yi9x*bm 7 k;dahay .gjf vdlane 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 engine?    W

  In audio and communications systemsl)t 9xervh7 9o, 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 frequencjd*y+2 gwnd zjag88q(kzur* 6y 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long between fixed pok4sd 3k;my sc; ,sbbkzg 9rq8+ints with a fundamental frequency of 440 Hz and a mass per3rmkby; b ss8 4+czqd kg;9ks, 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 filled w c+ve 04peg:5qmd z9hpith water (Fig. 12–35). The water level is allowed to drop slowly. As it doeghd+z 04pvcqe:9mpe5 s 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 m.:ez,iz9e+g9v bdkc kx4zcht- f4s-mass 2.10 g is near a tube that is open at one end and also 75 cm long. How much tension should be in:gf-4vd9ik , z+xckm ebthe- 4cz9.zs the string 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 to resonate kn7i y 9nd6op;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 vgj ai uif 9zk:)o:fa4pp(a0u3rr-;mrange coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is min-a aj(v)pm 0a:u;f:9gkropi 4iufrz 3imal 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 s98asq* dkbvqc gdw- 9- kitd(6tationary. The conductor on the stationary train hears a6qwvk-g9id*8d a stq (-cdb9k 3.0-Hz beat frequency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approaches yol3dem4 pf 81s5 eaik)lu is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant velocile4 5 1p)efk3a mis8dlty)?    m/s

  At a race track, you can estimate the speed of cars just by : lt)r8qujub;listening to the differenltb;u8uq:r )j ce 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?    m/s

  Two open organ pipes, soundin b,rou d-2m+il(3le*mmv6vd fg together, produce a beat frequency of 11 Hz. The shorter one is 2.40 m l li6dvbu2r mf*mv -dl+,(e om3ong. How long is the other?    m

Two loudspeakers are at opposite en iln75. p-sajtds of a railroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listens from thelnstai- jp 5.7 position A, in front of the car, (b) he is between the speakers, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in the aorta is normally about 0hc(8yrs(+u +jww7e n y.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and re (7wnjh8y( cr u+wsy+eflected 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 o52bi c6w*dzz9 /qdznwhile the moth is flying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of the wave dbqi 2w*ddzzn c 69z5/oetected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound pulses as it approaches a mos)3f/jiw-fww 0 b x+5vte5 opxsx ;:ppth. 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 o/; wet p3x)fx o05iwb5p+xvfw:- spsjne chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used v;uwz7l e+sk7eyq38pjqn /i g:phk4, to 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 73, 8qygkq:kuln 7ee+ w;4s/hvpi zpjonly 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 ste 8v *sj+juzud-reo listening can be compromised by the presence of standing waves, which can cause acoustic “dead spo*+-duz8sjv uj ts” 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,” involvexj)h;5ksa9 1qqs p0ic s 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,qp)qh0ka; 5cxs1s i9 j the rod can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the threshold of hearing for the human ear at a frequency of a/ z qqgatcjd dwm8ec8(t7 q7)yb6v38uboutu73tz q8v dc/ cw8 6ga7myqb8)(edqtj 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 observer on the ground hears the 0cr*rq,n4jpk sonic boom 1.*0c4rrjqp kn ,5 min after the plane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 1xt58erd3. 7kmp aonih)6s r8t5 $^{\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