What is the evidence that sound travo0r*mi :a;e9nam m+zvels as a wave?

What is the evidence uywull66b3wfe6a x *8that sound is a form of energy?

Children sometimes play with a homemade “telepff6 qfw9+ swxs1-2ylbkc +ht0hone” 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 clearly how x -6fhfwk 2f+sl qs1w9 b0tcy+the sound wave travels from one cup to the other.

When a sound wave passes from air into watgfk 9cv)7dxt:)vqz 3i er, do you expect the frequency or wavelength ztg):qvd v37k)i 9f xcto change?

What evidence can you give thaj3f zo2: mo;ado*l-uzt the speed of sound in air does not depend significaom- 2az*jodf;l: u zo3ntly on frequency?

The voice of a person who has inhaled helium sounds very high-p)i to sasnhnd95/2c,titched. Why?

How will the air temperat+/wa2l hcq )w*f +ej,ydahhj fs0-u; 0,k usjwure in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the9;o(l x m8jugd amplitude of sounds in various frequencyl(jdou89 x;m g ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer toget( odf.c8ut+ .nxf8( d yhnvl;uher as you move up the fingerboard toward the brifo; cl+t.n uv(d nd(y.x88huf dge?

A noisy truck approaches you from behind a building. Initialfo7+ 9 pikuaf-ly 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: Se uip-fa7o+9fk e Section 11–15 on diffraction.]

Standing waves can be said to be due to “inter2 3e. sc;oagkcference in space,” whereas beats can be said to be du.;s 2oaegk c3ce to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were loweredh9 8xkmgxzn0 0e7us.x, would the points D and C (where destructive and constructive interference occur) move x.u7xx 8hm00es nk z9gfarther apart or closer together?

Traditional methods of protecting the heari cw,lx.btdc q x)3:-bcng 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 device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise3b.)tqxxwccl c,: -d b. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig.dr-4(d: isr 7pmf t:au 12–31. 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 d4(-miapdrt s: :u7rf two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and obse+lg,2dos .gru .*-ec kpot4 lerver move in the same direction, with the same velocity? Explaip lu..ot d+ lgs2eog-*,k r4cen.

If a wind is blowing, will this alter the frequency of the sounl:5muhvl q-:*,awq svd heard by a person at rest with respe-slav q5q u w,l::*mvhct to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child inw*ctm/m q2 ht9aw0l*o motion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which position,*wm2/lhmoq*tc t0wa9 A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines ths k aew-)8z19h,b warve length of a lake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lakea1s8 k9hab wz e-w)vr,. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his kitui6;6z7o f/f3r xl 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 ocean at this point? Assume the spe63zrfixo7u6;i/fl tk ed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths pam zb:yrle l(7)vjah25h/ u)1u;d mrin 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 fol1,u z pal/5enggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. l1 pnze /5,aul12–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. Thett.06 ufhv d/s splash it makes when striking the water belosdh60vu. t/tf w is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to thecab 010o16wqwsb* m uk ground, sees a huge stone strike the concrete pavement. A0*sqbo01cb1k6am uww moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made(7js ntrw8 st5 over one mile of distance by the “5-second rule” for estimating the dist s t8sr5tj7n(wance 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 of8osu.w-w qx+w m bbeic-82r8o6ces(k 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 intensity.3ty6 g+vsnz(qoj z18wgg io5 is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneously0 +m;vbq4jdydg57eq6 oz ezv+,4qkpl at a certain place, what will be the sound level if only oyqplk qem zq+djev5zd0 ,4vb;o476g+ne is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally nomj(0c1 a6hkrq( oe o9misy 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, 0c6o meaokm1r( 9jhq(not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB:d9zsg74siu7 fjb qr- , whereas for a CD player:u7jsf- z4sbqg rd 79i it is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the powertnr8e;sw :w:;0diayh output of sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered o;tdew:s a : 8win0r;yhn 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 eardr-i33 91-dtsnde xs5ve-pi;l xuh n2c rum 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 more modest amplifier B is ryl zkt1 m(v.j-ated at 40 W. (a) Estimate the sound level in decibels you would expect at a point j ym-1 vt.k(lz3.5 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 dB3 j:m 6a).gcp.uinnww when placed 2.8 m in front of a l wu3 n).acpmi 6wjg.:noudspeaker on the stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound level of 2.0 dB. 6ix2 *+hqtrbp:*fb td What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Sectitfriqp bxb 6 :*d2th+*on 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will bmh-ny w hy gc/34w87tthe intensity increase? Increase by mwn34wygcb/-8h7t yh a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one ha i o,zgt76mrk7s twice the frequency of tmri7k gz6,7ot he other. What is the ratio of their intensities?   

  What would be the sound leveox88 tq7erj 3 f-s/ui9cuyc(ll (in dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at/f lruu j cts oy8i7(-c8qx93e 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem a5drm yws h zwr6f0m* 2(ao0ngz-f8,wms loud as a 100-Hz tone that has a 50-dB sound level? (mngm 0wrm wd*-s 68ry,(o52fzfzw0 haSee Fig. 12–6.)    dB

What are the lowest and highes flrhc6fo(9x7 g nn/q,t frequencies that an ear can detect when the sound level is 30 dB? (See ,79 (/fq6rgfn ox nhclFig. 12–6.)

  Your auditory system can accommodate a huge range of sound lev c- zsr pdk)a* fx2e9+ndize10els. What is the ratio of highest to dkr-c 1x*a0nie)z29ez+spfd 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 fundamechk ea)/5suzh2ucw6 zs 0 fp22ntal frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35euk6s/f 20h2ca hzcw2 5 uzps) g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are(+d8qwh ( k6wah bb1pd)jw*ke6sq( tp the fundamental and first three audible overtones if the pipe dde w 8*6hbhbsk(w+twqpp)1(qaj( k6is
(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 blowing across the tlw uj7* j*krn2r3lkmd..b l o0op of an empty soda bottle that is 18 c*r70k.b3 wu*kjlljno m rld .2m deep, if you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pipes spanning the range i cr; t;*n2cyhoo.vb) of humanohno*).;; c bcvt2yri hearing (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 of -m o+du zo.g/* wtkd3u540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its originag*3 .oz - wud/+doumktl length?   Hz

  An unfingered guitar strp8v) du1n xmn1/t4bdying is 0.73 m long and is tuned to play E above middle C (330 Hz).d1n)bp xd/yuv ntm81 4
(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 ,zkr,5bjg e1lkd;j f7 open organ pipe that emits middle C (262 Hz) when the temperature is,gle1kkz; r5j7j,d b f 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 d *vc ,e mjj8v.3j1err20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthzd927:aa lmu qt: z9g* faxo*ypiece of the flute in Example 12–10 should the hole be that must be uncovered to play D aboxaadt 2: mgz9**f9lzoay7 :q uve 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 gaq6z07ev *y7rcw8 okat 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in be 8e v7w6yog*zrcak 0q7tween. (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 l(5et fo 7aku*yt h)qy(ong is open at both ends. It resonates at two successive harmonics of frequencie(htq*yfo5 yk)7 a(tue s 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 -b .s7/ln sxvcfd;f 7f$^{\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 auz al+5zsm:wp (dible range for a 2.14-m-long organ pipe at 20 z(5wsapz+ml: $^{\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 thoahcd4 z8;c 6ev+4 7:dv ep r,hra5fyje outside and is closed at the other end by the eardrum. evchyza h, rd+po4cd 8 46:;r5e 7vfjaEstimate 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 stringsn65tb:(3cvll b3rx rb, one of which is soundrn3v6t 5bcbllx r:b3( ing 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 /xyhz du n*9y0Hz) 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 anot.20zaxjmjfc; k u 3d,wher (brand X) operates at an unknown frequency. If neither w;jc .wmk3judz2x ,af0histle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 ccc66bua/t3,65idpj bj sw ,s beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when soun65s, uwt,piccb 6d3aj 6cs/bj ded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension ir4yt. x2ixe0ei l nu880u4py yn one string is then decreased by 2.0%. What will be the beauiluyxx0iyn2 t pr 84.80e ey4t frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identicv6o)t, ) lmxtbal flutes each try to play middle C (262 Hz), but one is )vot) t l,bxm6at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. F 54/rz2 j+wtf7h1nr3 nrrxodc ork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heax23d rh4jt1 + c n5zwnfr7rr/ord. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A person stands 3.00 m from one spea f7bmvm:na5 /fker and 3.50vmb n7famf5/: m from the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed tsi2ydda(u 4r-de(+4 :gs ybqk o be vibrating at 132 Hz, but a piano tuner hears three be4 brdgyk :a( (-de qd2+sys4iuats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound of wavelengths 2.64 m ak/bkp -/ 0t,n dfhb+oond 2.76 m in air. How many beats per secondbk/oo+fpbdnk, 0t /h - will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 esvh6-wy;or ixxdd: 0j:f:- lHz when at rest. What frequency do you detect if you move with a s i: :wse60-xxd-ydf;vj:hor l peed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What fr3, w go;zv aberc87-toequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a3ogc;8wr atbe-oz7 v, speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz (f5rjbi :c(j; s8xvmbsource 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 they close;b( s8jxfcr5j bi(m:v? $f'_{source\,movine}$    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 equipp-k l (0b05qzx7jyz:wso6iryted with the same single frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency tlts0j(rk xy6 y0i7b:q-z z5wohe horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receives them ret o j4m:;9e5+tf pvktnaurned from an object moving directly awayf+9v5 t4 noekajt p;:m from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat emits an ult.uykj xtiu3j6q2 9v.p rasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected i.6jupv3q 29y kjt.ux wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, holx.or:z g)wpw x0: i-y,.:mdeup .qa tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone while at rest in the railway station. What beat frequency was heard if the train car approached the .ul xy.xqow, gdiow. e0 : -p:h)mrpz:station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measu*ntd5hf)rok0z/r w 8me,h7 co re blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of soo *nhe/mfc,o) 0d78hwk 5rr tzund 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 source?   Hz

  The Doppler effect using ultrasont.ix+vj n63gy:vp3yu ic 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 c af kyg:aq)):k/ k5offihq) 3velocity is 12 m/s from the north, what freq:fkgco 5)ahya qqk)k: /)f if3uency 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 its speed at uyc69yqr:x f:6v dow820 $^{\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 ist3kppw,hc ymc7y q;7fm 2w1b6)y o*ey 310 m/s (a) What is the angle the shock wave makes with the direction of the airplane’s mo*o 6tmpcm;7h kb,y2yywfp7wc3 1)e qy tion?    $^{\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 thhoy. ll9zt,qeijm +mfpsxv41k3u 53 1e speed of sound is only about 35 m93kiey hq,5mftv1p z.lmj4lxuo +1s3 /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/wm48xik3isfkp / kar.2an-55 dpaw (gs strikes the ocean. Determine the shock wave angle it (5k 5ais-pnwg28 /dkr3 ia x kf4wmap.produces
(a) in the air just before entering the ocean, $\approx$    (Round to the nearest integer)
(b) in the water just after entering.    $^{\circ} $
Assume T = 20 $^{\circ} $C

Show that the angle j gq;rf0) ufy,$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a pe81hrifn5kv 1lane exactly 1.5 km above the ground flying faster than the speed ofi 185khve1r nf 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 8).- xoo/jmzjsrv +zm that sends 20,000-Hz sound pulses downward from o.zj)j8xsm+zr-o mv/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 time between pulses (in fresh water)?    s

  Approximately how many octaves are there in t8 7v.ef/1iqhz x/znp jhe human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony)2vfo+l pr/ia hjke 2-s.c j winyu8*3. It consists of many plastic pipes of various lengths, which are open on both ends./wj2.a2ucj le-k* f3n os)i+p yvh ir8
(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 mau/-1tbkqe)dwtei 1b, kes a sound close to the threshold of human hearing (0 dB). What will be bud ,wte1e1tk/ -)b iqthe sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-dB sound /tg/lup0 d38b x2zp woare heard p08pz/todl/u3 wg xb 2simultaneously?    dB

  The sound level 12.0 m fr1fj hn 4ur0x:vom a loudspeaker, placed in the open, is 105 dB. What is the acoustic ponf 1x4v 0ruhj:wer output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The power/t3 mhlqh6iz;e d5l1j output drops by 10 dB at 15 kHz. What is the power o/;5h zdj6 li 3mqe1hltutput in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over tkul4 vvdr)34,oa*z znheir ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 au vz,ozr3*n v)kl4d4cm. 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 systems, the gain,: 3avt 4semw)qd7ktg:oyxw 8d*;hbp au4 l)+b $\beta$ 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 tsyq g9ze4o5cx9 m(l8yyb8j + ko 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 v;od74zj;c2uy t z73nddzwd+ fixed points with a fundamental frequency; d 7zdcdu7n43wzjto 2+y;dzv of 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 vibnd-1hqj e r09v*pi tc5ration above a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and agp9 te5*0jiq1rnh cdv-ain at 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of mass 2.10)i .eu k;sf;tba9fat(q )8exxcguqg d5a )1*g 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 produce resonance (in itscsf b1uxat)ug()q8e;)ggxa d kf ie.*t q5a9; fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to reson7q xv3z06su uxate 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. Tx 7d. ppw34fwk:il*zm: qq 9jche 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 fa3ipk 4 9xqcmzdj:7 l:.*qwfpwrther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The conductor ts 126*todsn df4mc9son the stationarys *m6ds1tst2no9cd f 4 train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approaches you is 538 Hz.kvkxj*q7b ;h 4uw+h:p After it passes you, its frequency is measured as 486 Hz. How f bv; kh+ p*:whxuq7jk4ast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars just by v imeclev93rz 4 +lr9;7tgb )ilistening to the difference in pitch of the engige+9v7 );lcb m4i9i ztrv3erlne noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11 Hz.99j9 krsjz4kj,i s rx. The shorter one is 2.40 m long. jkss49j9.r,jr 9 zxki How long is the other?    m

Two loudspeakers are at opposite ends of a railroad car as it movesuqo3tj qdgr,.9d j8uig s8;+d past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical s.qu+d d;gs 93uq8rji ,dtg8 ojound 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 flo9r;rsigt,c nd/ ntwt2b;+ +w ow in the aorta is normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from thewbd ;gn9o icr+s; wntr/t2t+, 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 speedf.c vbl/ :v9bcp4i n/f 6.5 m/s while the moth is flying toward the bat at speed 5 m/s b 9c. /p:vlc/fbfin4vThe 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 pulses as i;s*5u 6 dbb;6lw lz6u ys3kqllt 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 sodq;3;6 l5lwsb6s lbyu 6ulz k* that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to 4fw6o)3l;kjf. w;d nhi34 acmm 2kwsr send signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called th2ahw3d4orkmffm j sc6 kl) 3;. ;iwnw4e 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 cvmx4)v96vcbbt dej:l3 3iu2nt(j /e l,gt6d ean be compromised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a l/i936mvcj:4b2 jnb3 detxev,l6gd(t utlv ) e iving 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,” involves a long, slenj.wh5h.x xd2ew:g 32) ma edbgder aluminum rod held in the hand near the rod’s midbha:weheg.w2 mdx .)xg2 dj35point. 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 threshold of hearing for the human ear at a frequencyp3w2 ;pk g 0ou e6jin7cit*c8g of about 1000 Hz is6p; tn pcei23c7gjwo8* u i0kg $I_0$ = $1 \times10^{12 } W / m^2$ 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 boo b+z: kk8ssm3ghpjw l4(:1 iogm 1.k1(jg zpsmo + 3islwh48:bk g:5 min after the plane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 1/h7a3zrjbj - m5 $^{\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