What is the evidence that sound tra fh1tpndv ,kg;-g8sqai v(wyc;+c .9tvels as a wave?

What is the evidence that sound is ey t5+1cq itxchig;0;a form of energy?

Children sometimes play wo4 7-itoh*exg ith a homemade “telephone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain c*goox i-et74hlearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you expect the frequency1pakf+k( cndj,, pqa pp*84i im2 z4xk or wavelength to chapak pj *,kq2 4(4xm+ci1fdip,kpazn 8nge?

What evidence can you give that2h i d e is m(tyk+bl)npi(z*sz8bt149 the speed of sound in air does not depend significantly on frequency? i1)l8ey 9s tmz(n ibb*24ktdhi+( psz

The voice of a person who has inhaled helium sounds very high-pitched. :doersyq ,2 ,6o-hjngWhy?

How will the air temperature in a ps 7*r c/ijqf nfe )o52x1/cq fyi*2t1ll* auiroom affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplituw:wunhq ,tp 0 ua:s29 tc;qdj5de of sounds in various frequency ranges. (An exampl utpwaq;nq0jh:: cw,u9 5t 2dse is a car muffler.)

Why are the frets on a guitbanud(h :u6ux 03:w *hrwt9by ar (Fig. 12–30) spaced closer together as you move up the fingerboard toward the 6uwtu*da(0ub hyb::wx3 rn h9bridge?

A noisy truck approaches you from behind a building. Inm(shj9//cbnc j yab.yxdyq6; ) uw4.witially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffractio)bq; whj6.cyb 4u/ .y xa/y ws9(jcdnmn.]

Standing waves can be said to be duee 1xu9wz;a(bao)mh)7 jy 60sw8bvc nu to “interference in space,” whereas beats can be sae 68 ;ob)j )aywn9z(07u vm1sbwhxac uid to be due to “interference in time.” Explain.

In Fig. 12–16, if the fre ;mgp,1o /:bpgy7 oof lc.djn7quency of the speakers were lowered, would the points D and C (where destructive and constructive interference occur) move farther :71, /ofydo7mg cp.n bj;gl opapart or closer together?

Traditional methods of protectid4*cdz8 o9dfmng the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a 9z fdo8 *4mcdddevice is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thoughtb fyj64*)p3uuywn5b 2.l qutr of as a superposition of two sound waves with slightly different frequencies, as in Fig*u2. 4uybu5rp3lntfyj6b wq) . 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 observ7kj3sd kcn.m;er move in the same direction, with the . 7m ck;kdsnj3same velocity? Explain.

If a wind is blowing, will this alter the fr3rntrb/ uk37 hequency of the sound heard by a person at rest with rek3u thnbr7/ r3spect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a chky .fu g8p+xt 39bkzb,ild in motion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which p,p9.k3zxub f bt y+kg8osition, 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 ecs )z *c 9s23vsr1pf8bd(y jwzvho of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate93 bsp2v (*zy )j8sdw1 zsrfcv the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the sideb :yjr kkr,7m3 of his ship just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the mjykkrr7 ,3 :bocean 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 wacfrq oa5(m7hwn 370tu80cg bavelengths in air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is drifting just above a school of tuna o0 t(9 ni 0vnz0iq*uthhn 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 hearvin9nz ht0 ihqu 0t*(0d (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff.11vshf p8) oym The splash it makes when striking the water below is heard 3.5 s later. smfhv p1y1o8 )How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the concrete bk m8wqdy83,d pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and theyq k wmyb,d883d are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance (l+vgnq , .o7i ipiwc2by the “5-second rule” for es i ,ilqgvnio (7wc2.p+timating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 12. )6gi xwx ksfr5 2rl o3fle4k(qu5*yv0 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 s5kumf s cnhwh5 c073glht.(z6ound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produceh+obzn penp9q )6*m0o a sound level of 95 dB when fired simultaneously at a certain place, what will be the sound le*mbo h) 9p0o+eqz6pnnvel if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance frtqiu;ob,-w; er 5vvix;9wpl ,om an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this per;q-o5,uiwx,rt p; velb9;viw son experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas fl 8 l 7wyahrw575lt2wnor a CD player it is 95 dB. What is the ratio of intensities of the signal and the backgro7nw782awwty lr5ll5h und noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speak9eo *-p hdfgbt q5jt*)ing in normal conversation. Use Table 12–2. Assume the sound spread tj)tqdo5e- p b**9fghs 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 are4ef(()xni s)m sljpu- a 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 more modest amp6v-1cpw pk+pulifier 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 c-ppucv6 1p+ kwonnected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registered 130 dB when placed 2.8 ml+uz 4d u/ dt;q v;j*oi)qrfz( in front of a loudspeaker on the stagr) f*d4do;iz jqv+;/ qt (lzuue.
(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 differenwc ;xz6bg0) txce in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whosx6tg b wzcx;0)e levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will:ld( 65 hpvmza the intensity increase? Increase by 6:l z a(phdm5va factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement ajbhuni*3fqs (m 6g x,8k0 r02mqwg tp2mplitudes, but one has twice the frequency of the other. 22qju*q,0wm ms3g h8(kitng60brp fx What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that corresponds to /y)qxrl ex3qx9hol.: a displacement amplitude of vibrating air mo xohl.xq3 q e):l9yr/xlecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz t i 19ns58qedtu(xcb ;kone that h9qi51b(t8c; eudnsk xas a 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequenci(4mdr8 74.zont2 9psbugxtzm es that an ear can detect when the sound level is 30 dB? (See Fu .2m4 4szdttbr9p mgz7no8x(ig. 12–6.)

  Your auditory system can accommodo2.o4zq8d )y5swoib 8ht pdvw,p( w0late a huge range of sound levels. What is the ratio of h(0pwp8.ywv4o5s8h ,qot2lz ) d i wbdoighest to lowest intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental frequency of 440 Hz. The le9j 63r1x3 s5uhpprcvrbo4- byngth of the vibrating portion is 32 cm, and it has a r95xph3r4y6 u bc -spv3 1orjbmass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamentalr x*a88ube s4e and first three audible overton48se8 u* ebarxes if the pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you expect from blowx)m-7new ce ,pug4ul4 ing across the top of an empty soda bottle that is 18 cm dew)lc74e, 4gum-u xnepep, 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 avvcexs12. l) of human hearing (20 Ha .v1xl)2s cvez to 20 kHz), 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 itxry1i7-c brl +s third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of 1c+rrlxy7-i b its original length?   Hz

  An unfingered guitar string is 0.73 m long and is t;ya* yvf4o 1wguned to play E above middle C (3 f4*1y ;avwygo30 Hz).
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that emits middle C (262 Hz) whrkeoh9h3-4f i qid.x rs)b2i*en the temperature is 2xo9shr i2b3 ri fe.k)d i*4q-h1 $^{\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 nnah1.psm ;i1;,s :hv 9izjgx $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in n/r.yoop /up4p(yay7*oq )xoExample 12–10 should the hole be that must be uncovered to play D abooaqp*poy.ux/ r7 yno(ypo) /4 ve 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, x qc57y d6r wp/f1r c7-u(yogyeid++ m440 Hz, and 616 Hz, but not at any other /6 r+ cxd qm5dco e1rfi( yugy-pyw77+frequencies in between. (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 1.80 m long is open at both ends. ky,w9mx.vb,3o na l(l It resonates at two successive harmonics of frequenciexlv . walk 3n(m,9,yobs 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 p0az;ou9x 5 f3* bfbhj$^{\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 abp)d s.w0iv 9organ pipe at 20w. dip 9as0b)v $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 23i:x wbhx-u a*x-zrs 3.5 cm long. It is open to the outside and is clos:3-ix x3 rwxu*-hbas zed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to adjust two strings, o*.gtm9qcw07 f) gr)or vjt nj7ne of which is sounding 440 Hz. How far off in frequentn0cj9gjm*7g wv) rrf )tq.7o cy is the other string? ±    Hz

  What is the beat frequency if middle C (26 0dz;zp)f)m(y+gw o9 bcbg-sf2 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 atc s7lv;dp +g4o 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by huma gs4;cvp7lo+dns 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 whezpf/ldganb f rr 8 ,52f,lw6f0n sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency o,25bf 08a6,dpnl zgfffrwr l/f the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension a95yt2v cica 86yyb5fl ,dbb .in one string is then decreased by 2.0%. What wilylbfat .db 8,69c cy52vab iy5l 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 ghk0; c njz+ke8.:sqcto play middle C (262 Hz), but one is at 5.0°C and the otheh:qksjcz c;g0 .e k+n8r at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 44 0g5.7i5rtl;i bkcup5jh 3 rb*d:di it1 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What g3 .r7bi cldtib: r*k;d55 h05itujipbeat 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 perr; 7 urfhg7hd1son stands 3.00 m from one speaker and 3.50 m from the otheurhg ;1frdh77 r.
(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 vibkmg ,vo owq,e5;jjpn9 7cy,k1rating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the frequency of the othe, k;opom,e195jgcjv y,w nkq7r ?   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 2.6 19rt6a6te pz0q4t,7ln. kz9iw gdlnxyo) i)k4 m and 2.76 m in air. How many beats per second will be heard? (Assume T =d k7kqt)tp rz,w lya9 iong.n41)iz9xel 66t0 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s s5(vpf ,/yfebxw8 w4s tiren is 1550 Hz when at rest. What frequency do you dex 4pfw,t wvs5(bfy/8etect 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 you detect iflac11 hy t3zk x5d02dz a fire engine whose siren emits at 1550 Hz move2 tzakd1xl5 30hzd1y cs 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-Hz source is movin*9cjd 6uh8wao g toward you at 15 m/s versus you moving toward idjo*awcuh 9 86t at 15 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 single frequency horn. When oqyhv th-j sj hi7a;ff9gr u,mu*:i87;+kwsa 6ne is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the hornsj au9gw7,ivftrs :hs+6qy8ju; i ;hamh*7 -fk emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out uvbq-xxrroz6 0 .fg1 s:ltrasonic sound waves at 50.0 kHz and receives them returned from an object moving dig f6b0-ro. 1zxqsrx :vrectly 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 fly6 f( 5 kq*1+7vqk2vpbt fbnqhies, the bat emits an ultrasonic sound wave with frequency 30.0 f vp1kyq 6 v2b*(fkqh+t5bn q7kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba woe b.:t lcd.whv2mg8;as played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same t8we mdol .t .vhcbg2:;one 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 ulxphl;81m q l 1c;lctk)trasound 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 a1lllcmx ;kc)1pq; th8 rteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of frequenopu:e0i c5c 1jcy $2.25 \times10^{ 6}$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 wi*o pl 4k;n4njwnd velocity is 12 m/s from the north, what frequency will observers hear who are located, at restol;wjn *p4n4 k,
(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 its2z5ng5 :f1 f *d1zdyj oxku;eg 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 is 310 m/s (a) Whaf*pgh o3e.ub; ejb6a4t is the angle the shock wave makes with the direction of the airplane’s motion?gf;3b.e6u ja pe 4bho*    $^{\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 wrve r,l662y4lc lq c)phere the speed of sound is only aboutcr6ll2p,elyrcq)v 64 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s strikes the iut; kv+f hg egbhl+;ze3.07 eocean. Determine the shock wave angle it pr gfiu;hlgez the+3.0be+7 ;kvoduces
(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 p ke(j m.2 er*2uvl, p:38wdngjyh hm+$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overh2tz8)n xmcx p5ead and see a plane exactly 1.5 km above the ground flying faster than the speed of sound. By the time you hea ) 5txpn82mczxr 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 pulses downward fro*ahvzw f5jm9:t2 w7zgm the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 200 m, what is the minimum ttgjz:2* 7hf w9mz5vawime between pulses (in fresh water)?    s

  Approximately how many octaves are there in th9jdv a tn4h)8qe human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. 4qpe1itp vbz*k5h;hx . -*5qoqj-frvIt consists of many pla1k*qhrvxbvtp eq4 5hp-q ;f.-io5zj *stic 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 close to the threshold he6f3zbk6vz+ of human hearing (0 dB). What will be the sound level of 1000 such mosquifz+6eb3z6k hvtoes?    dB

  What is the resultant sound luzmg.h9/f0 rne;xpw2n5 be)mevel when an 82-dB sound and an 87-dB sound are heareef;pmn x rmz95) ngubh/.2w0d simultaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 g;gtygo0n(8:( 0nmtu c8 fifgan qu0,dB. What is the acoustic power output (W) of the speaker, assuming it radiates equally in all directions 0co 0unnguytt iqffg m,;g:(8 80g(an?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The pr(7aoglxj , .0no)m elower output drops by g jl ,)nomloae .x07(r10 dB at 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear prottkr,+/ (9fwoo n x .yu(vi.-nkagc, arective devices over their ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, +y r if.o((o,.9vkk g/a u nctr,axwn-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 communicati:f m*u5dr jb(aons 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 tu j8vy j+byb5.(kz nk jo8 cii9zav,2a;ned 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 i z ipzd4)u54gas 32 cm long between fixed points with a fundamental frequency of 440 Hz uza5z 4 )i4gdpand 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 fiwoc3, )riz/(/px xpbqlled 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 dir/(w/coipq 3 , xzxpb)stance 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 strz,v -j2bb1;do+fy bdming of mass 2.10 g is near a tube that is open at one end and also 75 cm lob db y;,d1 zo2+vb-jmfng. How much tension should 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 res7sfousn uq8b1c0,v. kkx of+,onate 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 sources. Thkf3z9cob3pq +e sound is loudest at p bzo39cp3kf+qoints 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. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train5aabc cjh e3vx -eao7d a*26q8 is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speeqxce-ac *abd835 hoj27ve6a ad of the moving train?   m/s

  The frequency of a steam train whistlen.aosqk jz*58wwo7x:4euq)p as it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving)7aw*xsoq jwu4z5pe oqn:. 8 k (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars just by listening to th 0+1b0jxgzuxx e difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (freuj1xzb+x 0xg 0quency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11 Hz. 5a h1tr.;av tjm7tdg7 The shortergr t5j v7a1. tamt;7hd one is 2.40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of a railroad car as it moves past a )d* ooy(zv reey*xolp9, 0,r rstationary 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 pass)e o*rvd( zrl ,e0yor9xpy,*oed him, at C?

  If the velocity of blood flow in the aorta is normally about 0.32 m/s what,w4x/crc h jg(i b- w:j;th-cj beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected xt; ccw4 ij /:hj --,(wbchjrgfrom 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 m*nn b./7hmndqgz ks jzr-8c,*2 p ac4aoth at 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 nka*-z4 g7/cs,haqd2nm zjpb c r8*n.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 pulses as it approaches a mot /hktnwj,+arw 4,m r0ph. The pulses are approximately 70.0 ms apart, and each is aboutthr+nm wkr,w4 0,a p/j 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to segmywd3/el 2mf +b.+p fnd signals from one Alpine village to another. d+./w megypbf 23mfl+ 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 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 compromised b6poyznu y 4x5j ;+d ycs3e+mb.y the presence of standing waves, which can caun+ +3c b4zpusm.yjy y;oxed 65se 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 standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” invo vx n+jjy6nixr.( 6.ntlves a long, slender aluminum rod held in the hand near the rod’s x. nx6v( nynijt+j.r6 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,
(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 tjtr,:xa/ oatju3ky x ;,1 *rbchreshold of hearing for the human ear at a frequency of about 1000jk,*;:t xj/t yrr3uc b aa1xo, Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on the ground hears the sonic g(mkootx h98 (boom 1.5 min afterxkg(9h8o(mo t the plane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 15 se x,2dlf m,t, hh4fj,r9a:ub$^{\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