What is the evidence that sound travels as a .hbo2 )qegi vh0 dm7(u h.owr*wave?

What is the evidence that sound is a form tz x,ec*s17kcof energy?

Children sometimes play with a homemade “telephone” by at z+ ,jw+qzhu55u q/ji;8uvxgf taching a string to the b+w85zuf5 ,u/iq+ghjuvjxqz ;ottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave pasg5ow ciemkxq.( g*m8. ses from air into water, do you expect the frequency or wavelength.(eowx mcg*5gmk8. qi to change?

What evidence can you give that the spee+3vgc.x/dk +pd1ubn dd of sound in air does not depend significantly on frequencybcgux +d.+vd3pn 1d/k?

The voice of a person who has inhaled he, xqxnsk:7di.lium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of organ po7q2 x ( opual c fmaes1g4rymt;;+7j+ipes?

Explain how a tube might be used as a filter to reduce the yc 3kqb1 63*1rpd ndg ikl9si2amplitude of sounds in various frequency ranges. (An exk c9ylnk33sd2p*g1rbq i6i1dample is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as qtmiyu hfb67wg13y dv1-ev wx4 lu* ilc2; m7.you move up the fingerboard m67-.c lw yl7qhd1uvf 3ei;1t* 2wumgiv bx4y toward the bridge?

A noisy truck approaches you from behind a buildin)gpjbiashlt .4 k7v 54g. Initially you hear it but cannot see it. When it emerges and you 4igsl v)hbt 4.aj7p 5kdo see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due torq vl:4 p)oy9q “interference in space,” whereas beats can be said to be due to “interference in 9v)y :q4qrolptime.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, woxzo x3in. -3gsrcz( d6uld the points D and C (where destructive and constructive interference occur) move xznxz36.r - gsci(od3 farther apart or closer together?

Traditional methods of protecting the hearing of people who work in area)joqw xha:x 30;2bw ves with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphonewv 23hbxxjo ;ea ):qw0s 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. Eac) s5ss5x-so9v e pr:ha luw7j9h wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) orsaj)s -wv ul79op 5:rsse5xh9 (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 1--eh+(p+bh :plawl9hnk:twv s sq1k direction, with the same velocity? Exha1ewv lpt (1sh-ksb-l:9+nhwk:q p + plain.

If a wind is blowing, will this alter the frequency of the sounlz/6b3n5c h wvd heard by a person at wlh6vnbc/ 3z 5rest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion onn98 +9smviiqn a swing. A monitor is blowing a whistle in front of the child on the ground. At which positim8 ns9q9 iinv+on, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echo of her shouegz;p7 *btjhil 53g2unp /ps;t reflected by a cliff at the far end of the lake. She hears t5gp u;nl/sgb 32 i;t*pzpje h7he echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the+fa 4c2( -f 1n s1mh:rqox:lmmjy/rpz 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 i/zmfr1 clo+p 4(mfm:nyj1-xq r2s:h as 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in airtp96js m2dz)w7yk* uy 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 r:g9u9h4e s 1(pld .3nsb mkopof 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 the backfire is heard (a) by the (o:ds bgl 4rhpp9u3ne.s1km 9 fish,    s (b) by the fishermen?    s

  A stone is dropped from the t e 7dmy bmsw8m+4vx,.lop of a cliff. The splash it makes when striking the water below is heard 3.5 svs,e.l8 mmdym 4+wx7b later. How high is the cliff?    m

  A person, with his ear to the groun( i v) r5m2u+(i/gccqc qdc/bjd, sees a huge stone strike the concrete pavement. A moment laiq)c/v+( c( /b2qumdrg5cjc i ter 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 error made over one 4)rzt2f7y6rrywznj 8 mile of distance by the “5-second rule” for estimating the distance from a lighr2) yr rj w7864nzfztytning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a ;fwf pg/i4ep i -qe-;vsound 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 of -c4qr qmd q .km ib(h,q29*dfza sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level yd 9 ,( cuh(gvjlldx-zfy(+g3 of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Ad3f xgy+ j-u( dd(hl(9ylzvg c,d intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally noisyv15 bf779572kda aufb1n xv2 fiqssia jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut 5fad91ub ias7 7vq v 2sk1x5i7n a2bffdown 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 dBt0i i10i(ozq(pp lxv 6, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background x010ziot(v l6i ipq(pnoise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in normal co2+. m0 neicdx (sb qm8,idu8sdv4m(atb7e- bsnversationmv0as(s,xeb q-ed m + 8.sb4um2i 78 nbtcdid(. 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 eardrum whose-xmaw+o: l8, l,wb2ev5yu wxn area is $5 \times10^{ -5} m^2$ (a) How much energy is absorbed by the eardrum per second?    $ \times10^{-12}$W (b) At this rate, how long would it take your eardrum to receive a total energy of 1.0 J?   $ \times10^{ 3}$yr

  Expensive amplifier A is rated at 250 W, while the mo o,ehp6a8izwc-egl +;re modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect ocl+,g;w ehp-eia 86z 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 whh0a4z:uv* w tzen placed 2.8 m in front of a *uthvz0azw 4 :loudspeaker on the stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound level of 2.0 /i(sla3f(-7wf(kvr uvx 2pxb dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 1i/- rvl2x(u7axf( ( fswv3bk p1–9.]$\approx$   

  If the amplitude of a sound wave is tripled, fp2g tnv59 7np(a) by what factor will the intensity increase? Increaset57g2pp 9nvnf by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal diey gu1z2l 9r)qsplacement amplitudes, but one has twice the frequency of the other. What is ther9q1)eul yz g2 ratio of their intensities?   

  What would be the sound level (in dB) of a somr8lu/2 sn xq8:vj+kh und wave in air that corresponds to a displacement amplitude of vibrating 8n8xlr:vu/qhjm2+ ks air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level yq fj o1pa9d,r*2 8ohvto seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fi9h82podav*yro1 , q fjg. 12–6.)    dB

What are the lowest and highest frequencies that an ear can depe hzy*a7qhk/v7 u9 c8-*f bfztect when the sound level is 30 dB? (See Figa-b 7fzy p8z*u/cfhq9kh 7v *e. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. Whlvq)ty: j3nf,at is the ratio of highest to lowe: l)yt 3jqfvn,st 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 fundaz wqx r4,54v +u8d wlzj61ofbymental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a lqw+wu4x8brd5of y1 4,jv6zz 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 first th2v r 98jryune4.+imorree audible overtones if the +yu8o9i2mv r4 enr j.rpipe 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 frequ/*qbm; b. 7y ; )k9t:wvv oa.ctfhlwdmency would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a v .awtvt.mwf9y lk; bbo:);*cmd/7h q 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-tubeqm* la /u:(crq pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the length *uaq rq:c(m/ls 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 third harmonic. What wil n3wmm (to / uv 8k791xq9nir5qghuo:xl bmo(n9kux h8qqin5ovtx /r3:g971uw me its fundamental frequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long (lkc b1z2 ,3(voc8 s0wjsfu0rry2gsp and is tuned to play E above middle C (330 Hz). b rks1(c(glv0orwz,2sy spj3 802f cu
(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 m-k. (dj xv;xsct .r/mbiddle C (262 Hz) when the .xmtxr(v bckj;s-d/.temperature 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 at 20 *h)(qi)f x(txt/z tid$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouhryq u,ug(71 j9v.yd r dqw0x1cy(senij(x:7thpiece of the flute in Example 12–10 should the hole be that must be uncovered to play D above middle C at 2rqxrue g(d9quj7 yd:whix,( c(v1j0yy n7 .1s 94 Hz?    m

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

  A particular organ pipe can resonate at 264 Hz, 440 Hz, and 616 Hz, bu omj +aap1aabp7+t,z 8t not at any other frequencies in between. (a) Show why this is an open or a closed +o7zb+pa ,aa8p1 tmjapipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube uvuz.6zs6:a l 1.80 m long is open at both ends. It resonates at two successive harmonics of frequencies 275 Hz anls:.6u v zau6zd 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 cma 2pcf-pj//2sigay4 /ai :a$^{\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 abb36 d:sq7 sj9kgqrq3 2.14-m-long organ pipe a gq7q3 b3ksr jbdq:6s9t 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 o7 7*9gb4yhwet lh/bkppen to the outside and is closed at the other end by the eardrum9h77*thlk b gp/ewy4b. 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 trn(50 s3du q.jfkegd.s ying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other d(j0 . gn.5fd ekuqss3string? ±    Hz

  What is the beat frequency if middle C (262 Hz lh1)rkbf2yt;8 e ag(h) 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 opkx3z,.8ig v xj7n f9fterates at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whisix f 7,g 9.v3nzf8kjxttle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork d;e8 rdrtgpmm c07 inj9 7re( br(0d*yand 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of th7 r ;ydpr *c igmb7mt(je90(r8de0nrde string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension in one s0)4( bd 1rf.jk e(uu trmz7pck54qihm tring is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–rjm)fu17 t erp(. h4m0 u bqz(54ckidk13.]    Hz

  How many beats will be heard if two identical flute 3-rhg0:5jrm: pv qd7knffmn6s each try to play middle C (262 Hz), but one is at 5.0°Cpndk0:fmqfm6:rn-h 3 gjv5 r7 and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a freq5dy 24sa mnik/hw)u x.uency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are soundi.suy )h dn54amx2/wked 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 1.8-/ ;hcm n qo2gga7xzcp(y/cy:0 m apart. A person stands 3.00 m from one speaker and 3.50 m froo:(x a7c/hn ggcqm;yp/y c2-zm 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 vi7qxcu7qx7)szx5 lshu 4 2v rqk yq;l i7o(+x(sbrating at 132 Hz, but a piano tuner hear( 7 l7yoqk zs qcq4x7(r5x7 s)xsuvluxq;2hi+ s three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound of wavelengths 2.64 mpdxjk997o1 myx:uz l0 8(gg 9utw7puw and 2.76 m in air. How many beats per second will be heard? (Assume T = 2 m7zd gwgxojtp9(xuuu 719:kp 0 8y9lw0 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a 4r dfk/:d:8bawn xnrsga828/ 7r gdm rcertain fire engine’s siren is 1550 Hz when at rest. Whara8sa :gmxb4ddrf r 88n7ndw:r /gk 2/t frequency do you detect if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do yoa +p :0s5prncst;:v hz.)e-qaq0qfa 8:wzkkdu detect if a fire engine whose siren emits at 1550 Hz moves at a speed of 32 m/s z05+kf)q8s a v p.tk :nr:sqdcz p0h: e;wqaa-
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving toward you at 1++c w(ur6klllxr z: l3xigz,ia9sbz4u u25i *5 m/s versus you moving toward it at r5s2 3gz(6liiuuluxl*b+cw,ilz+a:9x4rzk15 m/s Are the two frequencies exactly the same? Are they close? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with the same singlevoz2*c2vmmp+( o y 2fz frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at cfyv2 zo22m+ mzpvo* (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 ultraso zhn;q (ifu;l-bd m)0snic sound waves at 50.0 kHz and receives them returned from an object m0 zq l) hmfuid;;ns-(boving directly 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 m/s As it flies, the bat emits an ul0cx- vjfp)1avt habpvt a yhq,1-.- w:trasonic sound wave with frequencwxj 1,-p1tfb-hvcp0ha.-v):ytaa q vy 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving fco vz4 eo(ai 2k6p enmw1y)5,mlat 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 tae6y,o kie)4w5vc m( 1o2 mpznhe train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeikzay/ qx;3e, 7(cyasds. 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 expecaq c yak/xe3(s;iyz7 ,ted 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 ultras 1wpl -6bqauk/onic 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(6rpn*i i/g y yy.(tlr m/s from the north, what frequency will observers hear who are located, al.r(t6yii(y /rynp g*t 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 speez/7wt +jd lif,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 Mach 2.3 where the speed of sound is 310 m/s (a) What isc 9 dc(2ppdsg24p3m9pkakj9 v the angle the shock wave makes with the direction of the airplane’s motkcv(c ajp329 9psdp 4mgdk92pion?    $^{\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 ofrbx2ymf( sz/x:i ew v9 41hj-ad :goe5 a planet where the speed of sound is only about 3dz1m h9-j4g: yebr5ox(a efvws2i x/:5 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 thqz i) ,.s(q9jy*ql feke shock wave angle it pro 9qeik.(qz) y, *jqlsfduces
(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 1+/*t 9pkhl4 trnw3cassmi d2$/theta$ 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 almo; sx,o8z05s5ysvkswm; 1k bove 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. Determineo5xzsy ;s,mv1s sk85o;l0m wk
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device that sends 20,000-Hz sound n*ld;do)0xv;,njtie pulses downward from the bottom of the boat, and then detects echoes. If the maximum dep,;o)e; xd dn jvnlt*0ith 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 the4opn3ox .sxlm+7n;g v human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists ofm5: 1d4n;z2nf5nsq gtdvrl/ h many plastic pipes of various lengths, whicl tngd 4/rnd1sz5;f n q:h52vmh 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 clos:n cb.gv* 0q2jb,zadq e to the threshold of human hearing (0 dB). What will be the sound level of 1000 such mosquit0d ,b.q:zjnb 2a*cgvqoes?    dB

  What is the resultant sound level when an 82-dB sound and2jr7pehn/-n e5- blix an 87-dB sound are heard simultaneousln /e- rj lp25ni7eh-bxy?    dB

  The sound level 12.0 m f.aq( qp1ihlirxiu4k ,7r+wn 3rom a loudspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the speaker, assuming it radiates equally in all dixui.1,q +rk34lrnq (wi h7 iaprections?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The power output dehtt7 4xm570h4vias .l(ls mjrops by 10 dB at 1hi7 lvas4te. sm 0(75xltjhm45 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over thei ry9i:s p-py(gr ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the y9sgy-(pi:rp power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, 5.8x zbk6.zfr0xoy w:y b) kseun s/:tthe 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 tuneg0 0a7c clk+ 4u)yjz, n/apgwsd 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 cm long between fixed points with a funumd(u;uv0sjgn3(/p cu:+ amf damental frequency of 440 Hz mgvs;+(fm(3dpna0:uuc u/ju and a mass per unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration above a vertical open tube filled jl7m +*yov.p0rzedw 7with 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 forkpzy07wl7 jvmrd e+o *. when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of mass 3e , r fnneb/h6p9m) ds*wbuygy/u3s5 2.10 g is near a tube that is open at one end and also 75 cm long. How much tension shou /bn/35snw y)*ferhu 69 m,3bgyudspe ld be in 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 as one full loop mz;zs*x;f z2c ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz range comx.;8 f e nhj .-oz hqbjwafa:.f-g+4dfing 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 thatw. :fn+4zjj;.f-8h -hfg oaa bqx.fed the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The co,yin5 c7rb44fgq o,xxu7awu:hm 4r k/nductor on the stationary buqai:5c44gxorf x/ u7r,m n k,wyh47 train hears a 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 you is 538 Hz. Afte0lr 5cv 3c,efor it passes you, its frequency is measured as 486 Hz. How fast was 30lrcvo f,e 5cthe train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars just by listenzwhrl * uz)hh.lv4n.-ing to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as vz4lz.r-h)hwh*. lnu it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding togethefnby5 pmd*txi 87)c 0nr, produce a beat frequency of 11 Hz. The shorter one is 2.40 m long. How lo )fin 5bd*8p0mxncy7tng is the other?    m

Two loudspeakers are at opposite ends of a railroad car as it moves past a st/-oz)fheord, ;uf(v ,pqdokky1 sm ,) ationary 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) he is between the speakers, at B, and (c) he hears the speakers after they have passedzuo1-vkkof, ,f er/,msh; qdpy( o) )d him, at C?

  If the velocity of blood flow in the aorta is normally abg )(mfuzg(w 4dqey/8j2g a4 pwout 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 that the waves trag484u)mqa(2 wjzy w e /dfpg(gvel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at bh1 rv0z0ch 8pdm9vo3 speed 6.5 m/s while the moth is flying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is th0vb rhh13pz0c8m9v ode frequency of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound b b ar*4sjt 9c/ s2sroa6c+q/ppulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the t9b6o srr/c*ca 2 p/baq4sj+sbat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was onccle:-aksa/b8h olaw ;c*x;5be used 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 only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long,sb5wekh -al olx8c; b/:;aa*c 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 listening can be coc8l 5(m(yf fj mofr0i s8:i8a9cqhg3yx// obgmpromised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consf0/qscm8gaj(f oi9hf 8( o: y8byl/cxgm3r5 iider 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,” involvesfi,68 g mre*l +uce;rqc9tmq ;yshk5) a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod,+ct sf)irqelu kqeyrc 58 mm9g;h,;6*
(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 thres c yux*5k rl-vm :da8w2r,.gy:r b0;klnr5rkahold of hearing for the human ear at a frequency of about 1000 Hz r:r2y,wr .nd *5: g 5-yb0krlr8k ;lacuvma kxis $I_0$ = $1 \times10^{12 } W / m^2$ 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 soniu iziqiz5 3/lr0st3 -kc boom 1.5 min after the plane passes directly overhead. What is s/-izkq3z t uirl03i 5the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat 2u 9t06-fxbhxozofnd +1ox/i 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