What is the evidence that sound travels as a0ufmhkjla.dci+ 5 ;: srd,9hl sbl5o9 wave?

What is the evidence that sound is a f -1+q+q *1fi98ozdneksx c67uvx a3uikf oiu-orm of energy?

Children sometimes play wit p7*mtu 3*qt new :1.y*ugetzlmq6q4uh 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, qtun.ue6uqmq*el 7 wgt3p1 :z4*tm*y 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 passe.kk 1ns7pzd8i :h 9xjms from air into water, do you expect the frequency or wavelength to chani87phd9 m1n:s.xkk jzge?

What evidence can you givvc d5 u5+p7mnz-y/h;g8xwe scgc e3-z e that the speed of sound in air does not depend significantly on frequency?mc;-3 vzy e8cwg+ gs5xecd5-zh n /up7

The voice of a person who has inhal:s0 * ;pnic i)r5/d, hullndjked helium sounds very high-pitched. Why?

How will the air tempg- gvqn6 -bj;r2sa;, pm-tj4h6mhych erature in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude hu. dpljki,tk xc5) bg3 ic5(6of sounds in various frequency ranges. (An ex k.( pg)xic6j5t53c,u l bdhikample is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you s:9qtmll6 n *jkt;xrp/y n81emove up the fingerboardx:9ljneq* 1tnrp6l/8 km;s ty toward the bridge?

A noisy truck approaches you from behijbos d7:sx:1jg5zii/ q : b0qknd a building. Initially you hear it but cannot see it. When it emerges and you do see zj1qsxiio:s 5qg7b: :/jdk0b 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 to “interference in spd0 aafom1)ft1ace,” whereas beats can be said to baa1to 1dm)f0fe due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were ll d8q jvctynl.d*x o 1o6+2tu3owered, would the points D and C (where destructive and constructive interference occur) move farther aod*c3l16l nv+d .tuqoj ty28x part or closer together?

Traditional methods of protecting the hearing of people who work in areas with v + o+p0dqk.obdery 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 the ambient noise. How coulddp +db+k.oo0 q adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought of as 68j,hzyfk. sb) e1j0u,e fwak1wu i*fa superposition of two sound waves with slightly diabeyk16 i f80f) ku 1, s*whzfewj.j,ufferent frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler sc,ffymo 6j2 i(x90nh bhift if the source and observer move in the same direction, with the same velocity? (b,m ni0 9h2j6xcyoffExplain.

If a wind is blowing, will this alter the frequency of the sounyl9 4t0 zi-rz2jo op1bd heard by a person at 12j94oil zzbo-y p0rtrest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows variopd w*.qz9.(h+oxltb/ k scr+ 5ej:edaus positions of a child in motion on a swing. A monitor is blowing.r+ k +paj(toq *e9ld h swxcz.5b:/de a whistle in front of the child on the ground. At which position, 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 ec3 fmn)1 itsh. a)qda3hpvm73tho of her shout reflected by a cliff at the far end of the lpadv3t f3 )ha1i)sh m7mn3qt.ake. 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 just below the wa -b,6h * y6ndnlhhcykxdd63u-terline. He hears the echo of the sounucd6dnyhl 3 -,-yh b*h6n6xkd d reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelength+ rt;n64brzsf28 wrjp uu,h 5us 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 on a fog )ef(*ywj+hf vgy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elaps fw)eyfj*+ vh(es before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a 4-6yybqx u(db cliff. The splash it makes when striking the wateyxyq6b4db-u (r below is heard 3.5 s later. How high is the cliff?    m

  A person, with his ea-84ae5qzeru -c *l6mw:* bfe1 ifbj6x4kxm ypr to the ground, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, anqu6fjw p* fb4z* rli a8e mkeym5:-b4-1exxc6d 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 v,r t07 laluq7one mile of distance by the “5-second rule” for estimating the distance from a lightninga ru lt0q,lv77 strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensityp chdwc74)5m h of a sound 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 a sound whose intensity9f0;5pm y) vnezb4alf is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired aw,zc gy52b ya2i6ot4q rt/1ms*8kfm );ai y ysimultaneously at a certain place, what will be the sogk/mt *4zts;i6f15iyqy2yw a8 ,y rmc a2boa) und level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airpla dtmm.j:3xzh o-q1km 9e,hxi. ne 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, not dom - 1mkmhexh93x. j, ti.zdq:B’s.]    dB

  A cassette player is said)4g v,envr2yw 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 devicw,2)g rvynev4e? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a persbdm -kgg24 mg; wm1g sspwd)d16x;(cson speaking in normal conversation. Use Table 12–2. Assume tgm;)sd1 sk1-gw g2m(sdg; cp6w4 x dbmhe 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 area is qxl -(hgryvj; ,k 01xe$5 \times10^{ -5} m^2$ (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 :6fwzy)mpr 4 athe more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels y4:p zfrm6)ay wou would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registered 130 dB when placed 2yb h: r qr0fkv7p70y4r.8 m in front of a loudspeaker on the stabrq0 yv 0r7k: 4hyp7rfge.
(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 fwx*9 / ap mth2b,)kwrdB. What is the ratio of the amplitudes of two sounds whose levelh) bapr9w2* ,mkxf/tws differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intei.xftoj )54*kp ccqrkql,5q ;nsity increase? Increase by a f ) p5f.i4q kk*5o;lqrccjq,xtactor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have e4/eg tg),mlbcfoaf dk i - yc:-s:e;m:qual displacement amplitudes, but one has twice the frequency of the other. What is the ratio of their intensities?-ed c ;olcfm,b/ sf::-meg)4 :iaktgy   

  What would be the sound level (in dB) of a sound wave in air m)aku4c;w1 pm(7wcuxg e m.d6 that corresponds to a displacement amplitude of vibrating air mol) 1au w gcw;mu6 .pkmxd(cm7e4ecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level tufp0s9x m19caoxs9t 0ox: as9o seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. 12–6.)0 19 xs0mx :to9s9ac xfasup9o    dB

What are the lowest and higs/r vgq h3 waz,3kn.,whest frequencies that an ear can detect when the sound level is 3w w. 33 zsh/q,k,agvnr0 dB? (See Fig. 12–6.)

  Your auditory system cn , k 6mcnoutv72t h2bt/l 5)jcyj(jd3k. lwf0an accommodate a huge range of sound levels. What is the ratio of highest to lowest intensity attltc /kj2lw dj3tkn72 0mnhf. 5 vj,cuy()o6 b
(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. 2xj 3mas8zwt+lqs.8eag.au 1The length of the vibrating portion is 32 cm, and it has a mass of 0.xjm z8us.1.aa3 28taw ge+l qs35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundt c/0j s*hz(hp*3uf *5dlfej tamental and first three audible overtones if the pipe iu *0fdpth ls*hz3/5c *je(fjt s
(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 ydo5wgub3wdgvr/21lw 8n5(y ros(l /g ou expect from blowing across the top of an empty soda bottle that is 18 ggd/bwy2l5 gvo8ur l/w5s (n 1ow3rd(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 wi)) pdne4oep(oth open-tube pipes spanning the range of human heard eop4eo) ()nping (20 Hz 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 *w6qwp 4gmmp 88kw r h; x6mpx5cbu:k2of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its original xwmwcph4 qbp 2r:g6u*xm wk;8m6p85k length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to pl q(gvx 2 +nwh1lz6bptuts(.e 8ay E above middle C p1b (. tsx8n w( hg6tlvqzue2+(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 organ pipe that emitz 79r rq*zvas3s middle C (262 Hz) when the temqvr * sr9a73zzperature 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 5-hb8zsrmr 9eg v6z1,aua(jqwp5qd9 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Example g*n 7 v-/cf m/gadn3gv12–10 should the hole be that must be uncovered toac 3*-/fv7n/nvgd ggm play D above middle C at 294 Hz?    m

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

  A particular organ pipe can resonate at 264 Hz, 440 Hz, and 616 Hz, bu*2hlfq9fu /rx;qx/f b+ze3q jt not at any other frequencies in between. (a) Show why this is an openlej/xq+*3 z fq/hffrx;u bq92 or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1 ;imm2 2dl u9asonc-o2.80 m long is open at both ends. It resonates at two successive harmonics of frequencies 27u m2 od-o;snamicl2 925 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 q3vb zj2p ;b1wa9:yn*- unyfn$^{\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 etb+opfdxa16 ps)d5pk+xu + 69l mji*within the audible range for a 2.14-m-long organ po 9 ap+xdjs)6uk*1l d+ +6pbi5tpemx fipe at 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 openv/l2hut8y hb8 to the outside and is closed at the other end by the eardrum. Estimate the frbvh tul82 yh/8equencies (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 k 8kdfk.sid0(beat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency i0s8k. fdikk(ds the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz) au.r(u;adgx( .jx;q+ mmy0kbwnd $C^＃$ (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 mu)vm 2ms4( nc(brand X) operates at an unknown frequency. If neither whistle can be heard by humans 4smm vunm()2cwhen 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 tunilsl /2cgkb ,*/-ct iqmng fork and 9 beatsitql b ms/,cg-2 l/ck*/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are7u) owh h-pzagcu e k(8p+44s6naq g2+kqp/y b tuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eek- +qqyzk 4 o/(b28)p7 g +6wuuhapn4cgshpaq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play mirl2 yuafg n ilxg (xvbrj: g 3ykj:4f:13;)wo(ddle C (262 Hz), but one is at 5.0°C and the other at 25.rf41ox) y un:;w ji j3k3:b(vx:fagr2gygll(0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 j-h n0h0ze1lqhfxam vo5*pem07 u-j; 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 40ha e;-o mjjm5pl ux001 eqz-*hfv7hn Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A person stands 3.00 m from co.bu7/ g, nclkr; /pvone speaker and 3.50 m from the othru vol bgc;c.knp, 7//er.
(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 bvya9b/yu:spb6 : b8xhe vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are pla6u hbypysx:vb /:98b ayed 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 2.6i p :)gq/l4ulv4 m and 2.76 m in air. How many beats per second will be heard? (Assume T = 20 illvgp4u: )q/$^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 d:gy)n mmaqcm 0.1bb w2a 2:whHz when at rest. What frequency do you detect if you move with a speed h mcb1 2ay2danmgw wb 0).mq::of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a fire engine whose sivou2p)nb , 4+orpid 8bren emits at 1550 Hz moves at a sppinv+b28 4bro),po udeed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in;2;b ht2bixy ), n(wlrrcvmmz0.vi 1g frequency if a 2000-Hz source is moving toward you at 15 m/s versus y vixl yw(i r.,bcgnvbr)2hz12;m0t;m ou moving toward it 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 sya -anpwd/bxutnl 0 d3v 5d76+ingle frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rnvnl+7 bd5dt /u0adxwya p-36est 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 ultrasonic sound waves at 50.0 kHz and b. .odv nba*m,receives them returned from an object moving directly away from it at 25 m/s W .*adbm,. vnbohat is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a sza (zs7r7h.nv peed 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 reflected wavez zrn h.sav77(?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba wa ctk2la *;5 1az6t,df3mmdqzos played on a moving flat trai tm* 1a3m cd l;f6zoqdtk,5a2zn 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 the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultraso9r,g/ oay -6qr e1xmbrund 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 arteries at 2 cm/s directly away from the sound se61xr, /obg9arr - ymqource?   Hz

  The Doppler effect using ultt 9poprttp g0 /9+j*otrasonic 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 H,x1hpc ,nukm3 z. When the wind velocity is 12 m/s p ukcxmn,,3 1hfrom the north, what frequency will observers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if itcybn0pd av-wb bv98 ddjvk:;7nz::z.s speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where the speed of sound is 310 m/tx:p rkgswxpjl8d6 p *j89.5es (a) What is the angle the shock wave maxk:p5pgde * prsj8j6. x w98ltkes with the direction of 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 g5 lymt:w;c,o-j i 8dnsound is only about 35 m/s io n8;:5dy ljtm cwg-,
(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 travelinj4; tkswxki ;od .nw/4g 8500 m/s strikes the ocean. Determine the shock wave angle it producesx.jktwo k4d/wn;; 4is
(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 u p9ryr 9cd 5s7piaqky nm+cv 2+3:pt($/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and wjym 9s34nds0see a plane exactly 1.5 km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a h30d sy9jnw4m sorizontal 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 deviqqe47x3652 5afi zgcpa 2th 2ncerc+g ce that sends 20,000-Hz sound pulses downward from the bottocc4 r3cxg5+zeh 7p6iq 5 qen2tgf2a a2m 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 time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human auya-v-0p+ 0q g5 edwgqq9tqf7 cdible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consist:1-5ke8vas/tiik oyrs of many pla5s-k ter8 :ai1vk /yoistic 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 f9 6gv s3o1e n-g7v.b 2cmukxljrom a person makes a sound close to the threshold of human hearing (0 3l-b6 s c.no1k297gmvvx ugej dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound u(n/3 .gdetsv and an 87-dB sound are heard simultgsu3v (/e dt.naneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 1z 2n/s ,p ypgw8kl s*xxq.(z.e05 dB. What is the acoustic power output (W) of the speaker, assuming it radiates equally in all directiosygp2zn* es p8z /.kqxwl. x,(ns?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The power o27op w8s*g+bcfb7n qgwg7 ,m7 mb /varutput drops by 10 dB at 15 kHz. What is the power outpu*o pb8b 7cavb 77qms, gnfgrw2+g/w7 mt in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear proteke7s7g p; n;*meuzfm* ctive devices over their ears. Assume that theng7; kem*; uefm* zps7 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 power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications n(9rmw d1 hfqn-s(nn,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 tofo-2 j,vkx8ykvh5au j 2qr r*5 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 1- afryfsf4 cn7qkl1 (with a fundamental frequency o1 4f1 -fckfrsy(nq7alf 440 Hz 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 vliw0,qdfin6-b.*+w y1ovav a ibration above a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop sl f*b16qo, 0liwwa+.av -vi ndyowly. 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 mass 2.10 g is near j5,iu :xqc v1u m. on91hge 5hbuo7t,va tube that is open at one end and also 75 cm long. How much tension should be in the string if it is to produce resonance (in its fundamental mode) with ,t1o 5:ivn ,jxhg 9b1cqeo 7uvmuh5 .uthe third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one full loop (;e7z ns,iv g 3sxw0mh3$\frac{1}{2}\lambda$) 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 the01vq n7lqxvusm 5i+x4 500–1000-Hz range coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the qn47 0vu5+q1ls mxvxiother. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationa hb3ib* o7jo1jry. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed o1jbj b3 *7hioof the moving train?   m/s

  The frequency of a steam train whistle av,cts7b6c4 +u zpq h1hs it approaches you is 538 Hz. After it passes you, its frequency is measured as 486zsc hp4+1bhq u76vt,c Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars juslwqk4wq1 c:r7f, l- ;(qizybot 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 straightaw-,foc ;7bqwkiz y4lr :l1( qwqay. How fast is it going?    m/s

  Two open organ pipes, soun2o ;(.+ pie(xh j hikt9b0rmvqa/yy;8zdv 6wdding together, produce a beat frequency of 11 Hz. The short2/ t6ej0 hkd+;ywd(pi z. va(bymqoxi8 v9h;rer 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 pib+ksm4sy *2uast a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listens from the position A, in front of thei4 + kmyusbs*2 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 /f )m;;ftve ) z:ejvwcthe aorta is normally about 0.32 m/s what beat frecftz ; :ee/w; vvfm)j)quency 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 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 towar.nfq+cd+wh* a d the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of the wave detected by the bat after that wave reflects off fcqwd+ h n.a+*the moth?    kHz

  A bat emits a series ons uxif;3*n;z.g* oj hf high frequency sound pulses 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 jz.*fu3n;nig shxo;* before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used toq ,4f9jdnh9 po send signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were usep d99n,jqf4 hod 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 by a 0ouj ;efn+r:xedhtg0iwqkrtf-+q2 f: ,6p) the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, andpqqg f:u x:;6idefn, o0 rwet0++) jr2a-khft 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 demonstratar6 e 8zk6 t v3ofjqy0z)qbxmzw/6:h/ion, called “singing 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, ringing6fqa68t6z30h:zry)exbwz o/m / qkjv 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 th(i2 crk1d1 avae human ear at a frequency of about 1000vki2c ad(a11 r 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 gr m:ue0od) juuv728rv90n8 mh6 rcmlb round hears the sonic boom 1.5redoclj7)2m v06u80rnruv hm 9:mub8 min after the plane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is )wf 0 x;uwl2qf15 $^{\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