What is the evidence that sound travels asz87oltzpvq:aln) ru.5c8 o /6vd uc w* a wave?

What is the evidence that sound is a f;h9i5yblpjf +orm of energy?

Children sometimes play with a homemade “telephone” by atty8, nzn1qzx,zaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from on,,8zznzy nx1 qe cup to the other.

When a sound wave passes from ai gcy8kodqpv 8),f; s(jr into water, do you expect the frequency or wavelenso(8qpvk jdg;f ) 8y,cgth to change?

What evidence can you 4-nv1 fhpir+mp3y5g sgive that the speed of sound in air does not depend significantly on frhv -+rmp14pnysif53 g equency?

The voice of a person who has inhaled helium sounds79y2u* il h dyuk5g6;fh-nkve very high-pitched. Why?

How will the air tem sdtde(.0fi.gperature in a room affect the pitch of organ pipes?

Explain how a tube might be qg uht+/f raix*7wm 04used as a filter to reduce the amplitude of sounds in various0*i utfmr/7a+ xq hw4g frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you move/nu*txhfa2iqo * nh 2. up the fingerboard toward the bridge? ihnn/ou2x2q f**th a.

A noisy truck approaches you from behind a building. Initially you hear it but)ag 8m5jxiw r4vc1nm o;6szl1 cannot see it. When it eme sic ar14wzxomn5l v8; mgj1)6rges and you do 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 s + a(7q0rw1ved hi.czbe due to “interference in space,” whereas beats can be said to be due to “interf+h(vzwd1i.sqcr 70 eaerence in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowerew+1u:jnh0 xtlaa *ax;o3 ,f lmd, would the points D and C (where destructive and constructive interference oaj*3+m01x u ftl:h anxo ,law;ccur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who wor- botogw.w 4dc/jn ;:jk 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 ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to theodjnww .o;4j/ bc:-g t ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12v4/ou; crinv6t q ryt8c2;b:r –31. Each 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) or (b), are the two component frequenc84;ty:u vt iq6c crrn ovr2b/;ies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift zmx 3ug:is w.1j9cpd2 if the source and observer move in the same direction, with the same velocity? : g mwx j9u1.pz3ci2sdExplain.

If a wind is blowing, will this alter the frequency of the sound heap:2q* t)pxxq jrd by a person at rest with respxx :ppq2) qt*ject to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swingv/l h; 68z/lw mejy*gg. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear thj/hy6m l8 lg*wv z;eg/e highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echo ofcv53 .afk )lb7-r blp;s( pvzq her shout reflected by a clif(b5b7sqvr;fz vkl3-)lp.capf at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship )iqai5 ws p5,q++xr cdjust below the waterline. He hears the echo of the sound reflected from the pq5i)+d c+wsxira q,5 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 not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wa )-w)bd4i sxvv4ej; xxvelengths in air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is drifting just above o 0ew8 )q72lv qevy56 alftax;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 elapses before the backfire is heard (a) by the 2tl; 7o5fvweelv a q8)qyx0a 6fish,    s (b) by the fishermen?    s

  A stone is dropped from th ubsy*)bm v;r6e top of a cliff. The splash it makes when striking the water below ysvbbur)m * 6;is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge sto4xldzl w) ;bpqf,i )+;a3gfdlne strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in thedq dllx,); wflia+bp;34f)z g 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 zcj3y.w, n6nmof distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (a) 30ynj. wc3 n,m6z $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 120 dB? eip:1n/ k0nclw2 x8d 5rd sc+syg,(io   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 intif4 uj e-16ls/s5glcz zt(1ekensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when firbc,.h1v,h ia ued simultaneously at a certain place, what will be the sound level if ovh1 i,uc, ab.hnly one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an ai 3/8 ug *wkf tyiw zvt;,8o 3nq/y,xgir0qut8prplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, 8nf/g 38tk o,/0z3*,pvr tw;wiqg qy utxu yi8not dB’s.]    dB

  A cassette player is saif;42tsxv:tz zj yq0b,d to have a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 5802xbt:4z,;vfys q ztj dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound fro bwipyu*2l u64c9zu aim,50vz m a person speaking in normal conversatiy p5w bz valzcu40i2i*,umu 69on. 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 std e ( khd/b0t9/(g/wghxasd,srikes an eardrum whose area is $5 \times10^{ -5} m^2$ (a) How much energy is absorbed by the eardrum per second?    $ \times10^{-12}$W (b) At this rate, how long would it take your eardrum to receive a total energy of 1.0 J?   $ \times10^{ 3}$yr

  Expensive amplifier A is rated at 250 W, while the moryjpe;,3tzlob- zy 8.ne modest amplifier B is rated at 40 W. (a) E lypzo -,t3jb8.n ez;ystimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registered 130 d9c j :po a)5s63qydp2kbzt u2uB when placed 2.8 m in front of a loudydu6 bo2:tj9 53uzp2pkaq )cs speaker 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 typicm1 9akwqeis8zog(g66 ally detect a difference in sound level of 2.0 dB. What is the ratiokg6zos9ai6w 1mq(eg8 of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound w/dd3oc4ha/je( - jf2cq 6czufave is tripled, (a) by what factor will the intensity increase? Increase by a factor ohc 2z/3f(ao c/dd6-qfjc 4ue jf    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal d29 dr*sdge*zjv ff e.9isplacement amplitudes, but one has twice the frequency of the other. What is *v9g fdfsezdr9. *j2ethe ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that corres 7 id-.fplguy-ponds to a disp.-gli7 ufyd-placement amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seemez zm4/9bgsg3 as loud as a 100-Hz tone that has a 50-dB sound levelz9/gs4bm e3g z? (See Fig. 12–6.)    dB

What are the lowest a z8g hjxg.vimf(3v x.4nd highest frequencies that an ear can detect when the sound lev v.fmix38.4z v(g hxjgel is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levelsnyj0 zh5.m d7ugt,+5 zg r0ck3bn huk5. What is the ratio of highest to lowest in5n.jmu3u+d ky0b50 zkh5hct r,gz n7gtensity 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. Th8y85 vn3dt b) y;wbimxe length of the vibrating portion is 32 cm, ay b bd5yxm8 ;wn)i3v8tnd 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 first three audcub k8lxk*e7k5 x0.n vible overtones if the pipe is *0kkk8vx5 .eb7lxu nc
(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 buze*7,nrv ,kr lowing across the top of an empty sok *v7,u,zrern da bottle that is 18 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-tut fx0u-o 8m2m.o;vrmxk m3e(xbe pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be t-.xek0o fmxr(3;2uv xmt 8mom he 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 its0o6zw6g4i 2q 8-kjndhpfin ) a third harmonic. What will be its fundamentajwni2z6f ) ak8h-q4nio 6 0dpgl 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 and is tuned to play E a8b hk yh4vs(u-rv.z377vsdevot/jn* h+jmm 8bove middle Cv+/y7s-trsvu43.*h j k7n 8db(8mm hohvve zj (330 Hz).
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open w8+qzd)f3x:9 n/cy4 phwtob n organ pipe that emits middle C (262 Hz) when the temperature is 21hy:9t)8 /z+xp ncnw qbd w3o4f $^{\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 euvtql/y) p11 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of thintp s4 q(/z-uvu2r:ke flute in Example 12–10 should the hole be that must btknusu/p(z- ri 4: qv2e uncovered to play D above middle C at 294 Hz?    m

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

  A particular organ pipe can rek19eax:yc e(bsonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in betwkx9( c1 ebe:yaeen. (a) Show why this is an open or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80ujmki/0 5lg. j m long is open at both ends. It resonates at two successive harmonics of freque j5ul/mjg0k i.ncies 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 *;n pilvy7gns +q(3if $^{\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 wit*kp b6.rcr i8ijd(p90t i xmppftzju+d*(2u1hin the audible range for a 2.14-m-long organ pipe at 20pbr8dx*jt.ip9z*60+jk i(t2(uu irp1 pc dm f $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open to the outsidelu0( iv+j 7hj4dz*9mgdeimw (qkq 0 j0 and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing wavjv qg* e0mimjq097((ljw+ zhu4k0iddes 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 wheny: s01rj4ogu0c +qvai trying to adjust two strings, one of which is sounding 440 Hz. Ho +qri 0osj1 avc4:ygu0w far off in frequency is the other string? ±    Hz

  What is the beat frequency iy,sivc(ry1 a . sv)4rbf 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, while another (br/ wcq tx6gn2l61grf+z and X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill wh zc6+tg2fl61w gxnqr/ine 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 forn2 *9+1j,qc y ;1jyn)jf*criiihw m elk and 9 beats/s when sounded with a1jiyh;) 9 2y lwmjq1jen*rnfi, *cic+ 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to thie-li* *nnaf :28lbwe e same frequency, 294 Hz. The tension in one s*nwen-a8ef:ilil 2 b* tring is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be(dgg2 g 9sv0lk4: hlly heard if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other at (9 2g:hvglsy l0kd4lg 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. l+6 oxboj4bd ;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 +xbolj;dbo46C 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 1.8f)4cn8pv hku r c56xp,0 m apart. A person stands 3.00 m from one speaker and 3.50 m from the othh6)8 cpvxr5 4pfuc, kner.
(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 suppo:x4pajgcs(gznq0 d(9p tyd 8 ;sed 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 8a dygtx: pqjs4p0; z(d n(9cg132 Hz, what must be the frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound of wavelengths 2.64 m and 2.7 15 0ajvvtmc. dksn*mt4k*v/a 6 m in air. How many beats per second wi 5d*na/ k.stmcm1jvta4v v0*kll be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a ceh 1garz (b8*vcrtain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a sb cr8*ahgv1(z peed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detectycw-aqy5phs r-8m6r 7 vc+ ,t q/l-7lkxvp-kl if a fire engine whose siren emits at 1 r-k h, 6pcwalv+8y/ ypkt5--77v-clqsxr mlq550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000- n qjz;fbik8))fyy1c 4Hz 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;nb)f8yf1) 4q cyijz k 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 single frequency horn. When one ishqj 22y 0j3ciyfnp e;cq9 9/cb at rest and the other is moving towj 2yc3qcefq2 0y/cnh9; p9 bjiard the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonkclv2jfz-wk( dg195gd. /2 cq 8hqw veic sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25 k9j 85zcfwq2gv-/g2.w1dqd l veh(ck m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall a *3;qyg7ajcf: ovj7nwmd e,9lt a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the re 77y:vn,owc3ad*;gm9jlj feqflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moviu0qe;xr m 45b;iidt cjm;((cung flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone while at u;q04iu d(b;crm;x mt jci (e5rest 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 i zhp2:oir)pg)d+ 8chuses ultrasound waves 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 art chd+8pigroz:2i)p )heries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using 45pkr+)mo4xcnz6d(t4ogrveultrasonic 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 7lrb e*9 u, m:fefwt8pha3x:mm/s from the north, what frequency will observers hear who are located, at rest, exfrle: b9uftmp h7a:w*3 8m,
(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 movinh( e2 4fayn5zlg 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 speed of sound is1,oa)f6c rvmtsk+94 2mvk nxa 310 m/s (a) What is the angle the shock wave makes with the direction +voskm2ta49mf x n6,vc ) akr1of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmosphere of a planet where the speed of sound j zop(tll4t6m q7as2 r5scj6.is only aboutl j2pj 5q(lz6oss r4 7tac6mt. 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 85xc egp2drm8620 dpcm000 m/s strikes the ocean. Determine the shock wave angle it prcmp08 x22gmdrdcpe6 0oduces
(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 b t3 hympim7wn.4r p-j8d-q ,t$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a datx2y8zhjc+y * uk75 plane exactly 1.5 km above the ground flying faster y 5k2axdz8uj y ht*7+cthan 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. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device that sends 20,000-Hz sound pu/baxzes, /n )rey/ruv x zz,53lses downward from the bottom of the boat, and then detects echoes. If the maximum der/z na3zxb) x,/5,yee/vr suzpth 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 t: 6kb2v mnh;z;jt dhb,he human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists of a6blm; tu nnm)jn4at2 7o-m) jmany plao2lnn7bt nuj6 4)a)j m;-tmmastic pipes 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 cnmb q7c +i1z9jlose to the threshold of human hearing (0 dB). What will be the sound level ocq9mz 7j+bni1 f 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-dB sound are hevpb44; o0)s pi t d;hi-:kcgqeard sim oc4 p);4d t0g;s-kiqi:eb vhpultaneously?    dB

  The sound level 12.0 mz9e ) pfsuy/)* tr+qke from 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 directi+*quktzep) fr sy9)e/ons?    W

  A stereo amplifier is rated at 150 W output at 1000 Hph 5cke8ffjig t5d ;7*a-( vliz. The power output drops by 10 dB at 15 kHz. What is the power output in watts atffk (cv5hatl 5i *8-i7;gje pd 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over their ear/ g,e :9hicuq )qiv*g/dh,xu*jjuy d9s. Assume that the sound level of a jet airplane engine, at a distance of 30 )*e x,9uj igjdc /:*u9uyg iq,v/dh hqm, 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 communicationjwzfg3b0.9ozijd ;z/n *epr; cttw9)*arn n; s systems, the gain, $\beta$ in decibels is defined as
$\beta$ = 10log($\frac{P_{out}}{P_{in}}$)
where $P_{in}$ is the power input to the system and $P_{out}$ is the power output. A particular stereo amplifier puts out 100 W of power for an input of 1 mW. What is its gain in dB?   dB

  Each string on a violin is tuned to a frequenb284yf tjfj 0xcy 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 long7w ap d00wx*a17dtnku between fixed points with a fundamental frequency of 440 Hz and a mass per unit len1w0n* ax7ak7 udtw 0dpgth 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 vertica 5df xyg(eb:n/l open tube filled with water (Fig. 12–35). The water level is allowed to drgbdy:/( fn5e xop 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 is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of sy2-/ z e9,nsbt9 umlvmass 2.10 g is near a tube that is open at one end and also 75 cm long. How much tension should be in the string if it is to producszmv 9/9n,ls 2ue -byte resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to j.i) o59k6 hm*fwfrkd resonate as one full loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz range coming from two source2 msr sr1* bblyrh5bf2w6z 70vs. 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 minimal1yb7s 5hf2rl6vw*2brm rzsb 0 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 whuuukrty-/ppc/s-3 87bb wyj3 a gx9a7istles. One train is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What i/ybp - w txujk7 9s3 /r7aygp-3cuab8us the speed of the moving train?   m/s

  The frequency of a steam train whistle as fcbj qo18ij, 4isn8(+3 nbpjjit approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant velocityb+cq jo i3jnb481j (sjfp n,i8)?    m/s

  At a race track, you can estimate the speed of carr pj u2 vpw+ h3-,w4)dqg4lbpis just by listening 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 it goes by on the straigp)dvwq 4irhg 3pjl+wbu2-4,phtaway. How fast is it going?    m/s

  Two open organ pipes, sos(j:q8;p9 wdc+o;xfb. nyi nhunding together, produce a beat frequency of 11 Hz. The shorter one is 2.c8w;h.no:(ysfin 9bpj+qx ;d40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of a railroad car as it i ia *f5d9mp6zmoves past a stationary observer at 10 m/s a5m*i dfzpa9 i6s 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 passed him, at C?

  If the velocity of blood flow in the aorta is normally abourj 1eir +osn6;q a*xw/t 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 bqj r*ei;r1+on6w/sxa lood 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 flying toward the bv)ov,yg37l/ qszf,xqat at speed 5gl,fsqvx yv / z3o7),q m/s The bat emits a sound wave of 51.35 kHz. What is the 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 pulse 5m36ee l2+gajxm y:eskgu)y6ko w/i-s as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp returns bkeg 5 a/mi)yj3:6l +sy 26ukxegoemw-efore the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once usw8oprk5gv2: mia2 z/ued to send signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loskupom22w:ag iz5/ v 8rs, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundamental frequency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for sterb5 a(nvaur)6ceo listening can be compromised by the presence of standing waves, which can cause acoustic “dead spots” at b r6)ancu5(av 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 “sinbl2zto)u.bu )n x03eu ging rods,” involves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, loud, ringou)uen. z 0bl)u3xt 2bing 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 hu /gpy:4 awxka-man ear at a frequency of about 1000 H4yxa agp :/-wkz 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 t+ vydh w+khket- o*g74i/kh,e he sonic boom 1.5 min after the plane passes directe++e,gk 4y7h ktdhv/ *ioh-kwly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat i-n-9zge lm ydsw:s,7euj44ws 0: l+jgee2dsk s 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