What is the evidence that sound travels amr1vx gn(z u85s a wave?

What is the evidence that sound is a fr058wky fh-lform of energy?

Children sometimes play with a homemade “telephone” by attd iaud18hge ;;aching a string to the bottoms of1d dae8igu;;h 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 to the other.

When a sound wave passes from air into water, do you expect th*zz 9gvh9y kn2e frequency or wavelength to changz h2z 9k*9yvnge?

What evidence can you give that the speed of sound in kgz p0hl-p1b( air does not depend significantly (pl k -bzpg1h0on frequency?

The voice of a person who has inhaled6hbwl 8env )fk l/y2ua)su+a* helium sounds very high-pitched. Why?

How will the air temperatuyu.ksv6lfub w:1 3n8ere in a room affect the pitch of organ pipes?

Explain how a tube might be used at5udg5br12) p.c l2ryphu44rn0 isdj s a filter to reduce the amplitude of sounds in various frequency ranges. (An example is a car mufflujphdbldy. 0u tg215s2nc 4ir5p4) rrer.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you move p)qr( (m3bg 7m qs/dni8obrw0up the fingerboarbmrmb qps/n (8i(r7oqg3d0 w) d toward the bridge?

A noisy truck approaches you from behind a building. Inec d8l5.2ozt+on .w2,ad hgw pitially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “wl8+,an. zhoddwg. 2o2p c5t ebrighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be b,:v) nho2n oxsaid to be due to “interference in space,” whereas beats con h nxvo)b:,2an be said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the 4hb8;rwn73d (yu 7ryhq5mifr+d-z lv speakers were lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or closer ty3q-fv(z8ry7w 7d hb 4 +uhdmrr iln;5ogether?

Traditional methods of protecting the d/gh .38)v pvktaf*v thearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noisea/g htftp83k).vvd* v 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 could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can zcwgx.m1j1 ih yv e4p; 25i9xybe thought of as a superposi 1.vi2 1xphm 9;xzgyw4iejcy 5tion 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? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer movee8-+ cu :9gcg wfehi)1congo1 in the same direction, with the same veloci 1cg ne-o)f8+ cuc 9ewgho:g1ity? Explain.

If a wind is blowing, will this alter the freq xj+7w ,kmyi8tf6yav/ uency of the sound heard by a person at rest with respect to the source? Is the wavelength or8yax 6+tkvy, fiwmj7/ velocity changed?

Figure 12–32 shows various positions of a child in motion on a swingcdn dzd6 .k :caozm08q5j/ 8lb. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the cbczlaqmodd/ .5d6j:nc 088 zkhild hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening burgkgeikg ag;k,tmg / -(:,xe:5 *sxfor 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 rkki5k-g ;/,e*x,am ebsg:gt(g :ux gthe length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just3p h)makbzwe, 9oc, n- xt u//pb/ra1l below the waterline. He hears the echo of the sound reflected from the ocean fpo c ur/p/wna -,x9/eatlmb)k1,zbh3 loor 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 not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air)- )ybbm/h 0rouqb7kk 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 sch e/ xnczs43*3;prxwmhool 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 elapses before tsw/er; x4n33xpm* czh he 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 makes when stre 7lty g(w8khfi;)qu0 iking the wate0uf8 ey;lig7 )wkhqt( r below is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the concrqaa pvt3 g6nmwd79y2;ete 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? See Ta9vng waq6; y3t7dm2pable 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one )/h,+ (eer;m*olr/j nhuu j kumile of distance by the “5-second rule” for estimating the distance*/h uknuje(,j+/om uer;)hrl from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at dd; ukq r*n0w9the 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 sob 0/x;utvup (nund whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultanep kg s3s+favb( x07ln8ously at a certain place, what will be the sound level if o+7a8sxkn3 b(0s g lvpfnly one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equall4 i7o0h,mo)/izs yfrl y noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intens47r yis0mlo,h of/z)i ities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise rathr*tcrk 5(ii1ji0ga) io of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal an 5cr(k0ri )j1gi*i ahtd the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of souz6mr**mce /nc nd from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly unir*nem m*c6/z cformly over a sphere centered on the mouth. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave strikes an eardrum whose 7g unusq;(,-0phft shoy4 +saarea 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 ra)k*zcesgvr2h. t0 sq+ ted at 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to e0vs) 2zh.+ctkesqgr* ach 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 )gi:*bwlzian*:zfccbx+be/ / u 0ab( meter registered 130 dB when placed 2.8 m in front of a loudspeaker on thz:b:agx cn*b ifbz l/*wi+uacb/( 0e)e 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 de, nx6is3mah6g+frv8fagq , ,j9v 3a-f7z ltzmtect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds n zl+76rmvai6zv g- j9 38sm,qtx,ah ffgfa,3whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tri11h)ym v.a (ieabxv /hrhur+,pled, (a) by what factor will the intensity increase? Increv.eyhru/hrix1h)(, v1a +m a base by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement ag.yyp/ 0j b 3v7lre2msmplitudes, but one has twice the frequency of the other. What is the ratio of their intensi gml/e20 y3p7 bsv.yrjties?   

  What would be the sound level (in dB) of a sound wave in aywi;j3o79 ( ira.csqqpo y29ci 1ag /bir that corresponds to a displacement amplit ;sg39y2ywi9b o(i ca/p7rjqoqc i. 1aude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what s0 hdb3+vo66yuu9ku k,e0hxl o,fhsrq 79g+rm ound level to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. 12g9 ur9bqm+uv6urf hyho00k7x63sld+o,kh ,e–6.)    dB

What are the lowest and highest freque33xe. gd3kl6j gwn n)g zp9t+rncies that an ear can detect when the sound lw 3r.jgt)3zke9dgn lpn x6g 3+evel is 30 dB? (See Fig. 12–6.)

  Your auditory system-2r 3:; p tjhxqmr, nxr2yk4wo can accommodate a huge range of sound levels. What is the ratio of highest to lowest ix k4nr y :pmwhr3ojx2t,2-qr ;ntensity 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 length yq;j8hi78ni r/o*0l- f jrtkf of the vibrating portion is 32 cm, lij i /jk-0ytnfq7*8 oh8r;frand 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 fundamentm.t k/ f 3bkdl1cav.j hy;9n4ral and first three audible overtodv;f31k.tck4l9 n /ymajbh.rnes 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 expecpqh4 y y ;+siqnhy,b8.r3a/enfkl p51t from blowing across the top of an empty soda bottle that is 18/1ilh;3y + qay qfy45snp8.rkpne bh , cm deep, if you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pipes spanning the range of hu811ezi 2 izzwcman hearing (20 Hz to 20 kH ic2w 1iz81zezz), what would be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its t3zd-l t2zt89 v2f9nydmxx vho 7- 2zcnhird harmonic. What will be its fundamental frequency if it is fingered at a lengo fztv9x2dtlz2m y2xn z vdnch93 8-7-th of only 60% of its original length?   Hz

  An unfingered guitar s,.rnze uk2 .;89eoneh1obotmtring is 0.73 m long and is tuned to play E above middle C (330 Hz). rno2h8.moet,1e;b .9zno kue
(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 f4qiuq 8m3facf y:+lk)9cpy* j )q6gemiddle C (262 Hz) when the temperature +eu)84p* q6q aiq3cglf )ycjmff :y k9is 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 3 1g8q(1fsvemsw e ga*/zy,ruu+0jz eat 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute i++a p )7asj zn27icneln Example 12–10 should the hole be that must be uncovered to play D aboas+jie a)pn z+72 7lcnve 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)5r saz2 y 3tos:vodg(, and 616 Hz, but not at any other frequencies in between. (a)(z s2:vod)yo 5rsat3g 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 1l6b:zfh ,ym .o.80 m long is open at both ends. It resonates at two succeh6:y .m,foz lbssive 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 ( kd j;goarreupr ,+2s;7+cxq$^{\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 orfc vqb l2: lloua*;q.+gan pipe a;.cvf qu: q l*2oall+bt 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 openb;1tfb 06b1xm1my xd (twg0mj to the outside and is closed at the other end byg(tb 61j;b0ywm1bfxt0 1xm dm 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 nhq6. rt;w+vr v2n3vxc6e dh/ every 2.0 s when trying to adjust two strings, one of which is sounding6.v2dtvv3nehqhr xc rn6w ; +/ 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if mid -j09uxmo.zz tdle C (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while another /q y9(ab,uqjij7wl d)(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 occurqjq /y(d)ia9wl7 bj,us when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 8yx36k 61rmvyddmf-m 350-Hz tuning fork and 9 beats/s when sounded wikd 8yrf3-1yvmmd6mx6 th 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 one sfn-r2xavyb/1l j.zx wu 3r/ a)tring is then decreaseuabanr j3/v/.2x-f1lzwxr) yd by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play ack(m0.x8wvb 7nlv 2w ds0r s7middle C (262 Hz), buw7 02lwv.vrn70x k dsa (b8msct one is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has al7mqw r t 9/ziy.kp+*u frequency of 441 Hz; when A and B are sounded togetliq7.t+z prm uwy/* k9her, 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 stkilac- k;;x p;ands 3.00 m from one speaker and 3.50 m from the other. x;ca klp -;k;i
(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 vib48x3f f69cmk z xcm vtc1k2fy(rating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they 4t6m vf kk 3f(x2y cmzx819cfcare 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 c0*/e p4auf a, xyvx; zzp(*a:g8luonwavelengths 2.64 m and 2.76 m in air. How many beats per(xya*:* lz; / 4a0vp pfcguuz ,onex8a second will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s 4axkd9z,r cjx,v+1jf9mpo ,xsiren is 1550 Hz when at rest. What frequency do you detect if you move with a speed9,o4+ c kjxp9z1 f vdm,rxxaj, 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 io*9 a8(s .2oopdi jyrfire engine whose siren emits at 1550 Hz moves at a speed of 32 m/s ir(9.*ysao8 2i djpo o
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift inepho /.wx*(jlrrz . xi-8)xme frequency if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are thr8-pl/ .mxj. w )ixh(oexze*re two frequencies exactly the same? Are they close? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with the sam vh7,u+.:vly2mi 7;y ykb zqmie 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. y :i7bvhu 7m,iqzmlvk+;2yy 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 9gka5 g8n u(kzbcxf+k 0 +dmo-at 50.0 kHz and receives them returned from an object moving directly f g m0nc8zu+a5k(o kkd+xb9g- away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m85pr u xjbu;lj: .nl3,mpkf4w/s As it flies, the bat emits an ultrasonic sound wave with frrj.:b4x;jlul nmu 3kpf,8 pw5equency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler (q)sxx4klc h n+5vp- r6vdw g,experiments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the sp)l,dcr(6vg ws5k+xh -nvq4x ame tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure bk l7eux( qm:c6pr j,a8lood-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 6 q(,pa:m8lr7uk jecxat 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of freqf7 p,jco ex;vfx(chcw.8 go+1 uency $2.25 \times10^{ 6}$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 1 + etc+ox6m9dd1hj ziwind velocity is 12 m/s from the north, 19 thzi+e1 x6m ddjoc+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 itikn uvlkmw7, r c/jqd-5 p9gi(1h* ,on land if its speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where the s(-y:ruh aqgzy n,eyh+a 8ty)2mgg r/(peed of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of the airplheyy+ 8u:g n(h 2-taga,zyyqgrr )(m/ane’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 ) l-s r/c mj/szk )4 r0dvzs:1fogr+lka planet where the speed of sound is only about )l sj: +/ck-s)ov/zzrkf10rmr4 sdg l35 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 shock wave im0s b-6oe 1hsangleo-sbh1 i es06m it 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 /pbd0dz4s9yanzp r:d*l2 ;e o$/theta$ 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 km aug ):l(wa ,uh,ona9jhbove the ground flying faster than the speed of sound. By the time you hear the sonic boom, the pu(gj ow)u h,h9:la,a nlane 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 hlxj88y;r . thkyu( i7that sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 200 m, i88 j 7y; lk.tyx(uhrhwhat is the minimum time between pulses (in fresh water)?    s

  Approximately how many ommr (bfkx9o o+x89 dp6ctaves are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists of mp4*v;4 tbhh mxsg;jvi2abq8:z6ab v(any plastic p a;4zbbq(pgxt 6ij hvs 8h;b2vvm*4 a:ipes of various lengths, which are open on both ends.
(a) If the pipes have lengths of 3.0 m, 2.5 m, 2.0 m, 1.5 m and 1.0 m, what frequencies will be heard by a visitor’s ear placed near the ends of the pipes?
$f_{3.0}$ =    Hz
$f_{2.5}$ =    Hz
$f_{2.0}$ =    Hz
$f_{1.5}$ $\approx$    Hz (Round to the nearest integer)
$f_{1.0}$ $\approx$    Hz (Round to the nearest integer)
(b) Why does this display work better on a noisy day than on a quiet day?

  A single mosquito 5.0 m from a person makes a sound close tojfcnv0zd 0q26 the threshold of human hearing (0 dB). What will be the sound level of 1000 such mosquitoz26j vd fn0cq0es?    dB

  What is the resultant sound l97ui7plf)x pl evel when an 82-dB sound and an 87-dB sound are heard simu7)97 ilxplpfultaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 dB. W 7 ;ff2amue 7;zx2rcdrhat is the acoustic power output (W) of the speaker, assuming it radiates equally in all dire 27xf2u;d acfer;r m7zctions?    W

  A stereo amplifier is rated at 150 W output at:u2loy lc,v 4j 1000 Hz. The power output drops by 10 dB at 1:vl jocu ,2l4y5 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devipwj:u8nms;m5 mg t1 0kces 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 1:g0s8pt m mn;kjwmu5has 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 sys4l ps)xzdtwf, +-spc4 tems, 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 tuxm*fx rtj9e: ukgih/,(a z;-lg. 5cphned to a frequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cpef*si1 k,c. pry/ 7*li eggz.m long between fixed points with a fundamental frequency of 440 Hz and aicf,*pp*zye1isgk.7 l/.egr 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 wf345k8i( ik7juwbsgxvu;v,z p0.ur open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What iivbpxs 8.k 3 5zu(g,j7u kiwv4;f0ruws the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of mass 2.10 g b a6d ipel 0bcl(wsp;7r0*vh,is near a tube that is open at one end and also 75 cm long. How much tension should be in the strin; b,p (lch06we7b*v ap0 lridsg 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 as one ful(:;*d o-pxcc d .okxf lirh0y,l 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 purts,bw (zpu /(av.qq)l e tone in the 500–1000-Hz range coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other.s b(.z laqwt)u(p ,vq/ What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is statio6hh t1qg 6gt0tnary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of the moving trt0tghg1ht6 q6 ain?   m/s

  The frequency of a steam train whistle as it approaches yo3tg7+u he *fqhu is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How ff*e h qut+h3g7ast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate t5g08 3wka p0mpib0pbvhe speed of cars just by listening to the differw ba00bppgkv3i5m8 0pence 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, sounding together, produce a beat frequency of 11 f- b ,6aqn 0m*vjmku(z e:cc,qHz. The shorter one is 2:qezc,*-k v ,mj aq6 ucmnf(0b.40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of a railroad car as it moves l p)cx.;;a oixpast a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identica) axl xi.;poc;l 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 thph+n4tty7 3zlv7nc/ se aorta is normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasoundc 7h47 l3sn+ npv/ttzy waves were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s while the moth is fl *xa),vfc whke..va19 rmhs.6ysds)q r vyc,;ying 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 detected by the bat after vv ,9r dfak ecq)sw .hv.y.hxr6my);c1,s *a sthat wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound pulses as it appk,. m pdg.j1,m0tpu8-jctv bu roaches 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 returns before the vmt1 p.8dgc0 kub,jtju,-. mp next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signals from one Ahqj*( fh-s8yelpine 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 y8(fh-sh *qe jof this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for sterzb *9 lb*t;pmfeo listening 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 fundamental frequencies for the lm t*9bzp;b *fstanding waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a loo ;j2.3gfo+ 3heb av2cqiead +ng, 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,” a+.god i3bovj32efh q+ 2ae;cor 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 p-bee 1f kue9+x65ogffor the human ear at a frequency of about 100ff bg-+59k6eo exp eu10 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 groukh* (1ay3a2uaaubui 3 nd hears the sonic boom 1.5 min after the plane passes directly overhead. What khyu1a (aiaa* 3u3ub2is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedbo9s-d aq)z52w mk: tohzat 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