What is the evidence fdfaw o 3yg88 wly6)-ue0 xn7wthat sound travels as a wave?

What is the evidence that sound is a form qp b7i)bgzv/./ rwq) wof energy?

Children sometimes playmk b0 sf9 +ha:riv6(dp with 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 clearly how the sound wave trbk 0(9i6vd :ms+fphr aavels from one cup to the other.

When a sound wave passes from air into water, do you expect the frequency or wt d2tdho1s2 8tavelength to changts8d od2th 12te?

What evidence can you give that the j 1 mqn xhrjs6z:9k:2cspeed of sound in air does not depend significantljrx::sn9 k1j6c2hq zmy on frequency?

The voice of a person who has inhaled helium sounds very :)hwf ,xg usf7uvqav)w3 4-lj high-pitched. Why?

How will the air temperature 1ifw-u6fk-bg in a room affect the pitch of organ pipes?

Explain how a tube mig+/ jjbkkb, 6nxht be used as a filter to reduce the amplitude of sounds in various frequency ranges. (An exa/kb6+x kjjb,nmple is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced clossta1m/ 7 bjfxz6 ze -:2cnd:zier together as you move up the f:fc1jax im6s ze2z 7 ntz/b:-dingerboard toward the bridge?

A noisy truck approaches y,s uq / g*e(+8pm 3tyftqagu,dou from behind a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound ise,sqpm 8a +q/(guu*dg,f t t3y 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 “interqiq+10+.cw-l 3 fqckqd zs-yrference in space,” whereas beats can be said to be due to “interference in time.”qi3q0zf kly.sc -q +-cr1+ wqd Explain.

In Fig. 12–16, if the frequency of the speakers werr hru-;qo ;j-wbjjr8 *e lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or closer together?*r ;jrrh-wjju- oq ;b8

Traditional methods of protecti 5t2cgszt2np0ng 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 device is used which detects the noise, inverts it electronically, then feeds it to the heats02pcnz 52tgdphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shwf g gtor++46fown in Fig. 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, ( +twf64r go+gfa) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in the same dilz2;airbl) 4zmhasz+,yz. n: rection, with the same velzslzh4lairm+.n2; :z,aby )z ocity? Explain.

If a wind is blowing, will t,5cwrxt2o6wix0 t7zj his alter the frequency of the sound heard by a person at restw5 czx tr2 6wixj7o0,t with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child ;kh)yh;t6z +z feeao1in motion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear the highest frequehke 16t h+ z)e;fzyao;ncy for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening ) d*gj.xv3 7eltxcc /qfor the echo of her shout reflected by a cliff *.7lx 3ejc/ g)xqctdvat the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He hears t27 fx5dwc d+hahe echo of the sound reflected from the ocean floor directly below 2.5 s later. How dddfa2c h57xw+eep 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 wavp 0, r2cqmu8-t(tqvej0 * ghcqelengths 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 tun4 2ih odah49dda on a foggy day. Without warning, aodai 2hhd494d n engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. Th y)sgto( /wycu,v43 oue splash it makes when striking the water below is heard 3.5 s latsc yuo tw(go v)3,/4uyer. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stx3a)h4.r .0bobe* s weyo3 wixone strike the concrete pavement. A moment later two sounds are heard from03.woex.) 3rbxhea i*b 4yo sw 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 errrfkh wu , c1lcrm w:l9zta6(;;or made over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (a) cakfl;rm(: zhu l96w ;,1w ctr30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of7sa9u ) 3s .pri txp:amw36akj 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 i5(wm.slg w 1 xeqdyab6 3j2ol5ntensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneously q 88sj,+sr0z;c oivflat a certain place, w;s zr v0+if qjo,8l8cshat will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a cer-vcz1laa:zlfu*8 l,nz -:oi mtain distance from an airplane 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 shfl :lo-zaicz:1a-z 8m l*u,v nut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player isw2s/q8news7 tb iob.o)+oc, cbz: zz: said to have a signal-to-noise ratio of 58 dB, whereas for a CD plae s scz8 c7z/wo2)nz+wbq:bbt:oi,o.yer 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 power output of sound from a person speaking in normal conversaop byxp3ah46m*e 5y s 5gxpd4yo5 q:/pt45 6 4xyodoph5g:p /e 5mpy3sp byxaq*ion. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the mouth. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave strikes an eardrum ws;dec(/u(qi 4. aw7j psr-qxzhose 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 isz * x;z-lqpgk-pjdfl:1wa, 9m rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker pdlzxk-q91pml:-; gzw*a jf,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 do lq ,3/m0feh:ert6ttB meter registered 130 dB when placed 2.8 m in front of a loudspeaker on the stage.3 tfe :o6/rttqm0el,h
(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 71cup* pm*;unqlqe0 ain sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]7q;pu pal qe1ucnm0**$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the /ze1;j7h r twd.lrgh8 intensity increw rl8djt er/.7hgh ;1zase? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twi+ff( :cckrc cru.sq47 (r*icx ce the frequency of the other. What is the ratio of their i c(ccs r(cfx:ru c*. iq+kr7f4ntensities?   

  What would be the sound level (in dBqazd3b)2 ,v fv) of a sound wave in air that corresponds to a displacement amplitude of vibrating air molec abv3vzd)2 f,qules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem acoyhkxw41,fx m, hn 4-u )m5a:c8mtrqs loud as a 100-Hz tone that ha,5h 4c8okmrnu1,)xq -tfymhc xw4 :ams a 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that gkhpvkp wb(9cw*l/s7y1 ys: 7an ear can detect when the sound level is 30 dB? (See F pbk pgy :ycs*v(wh s9wl/k771ig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is, s:q9tn euc0ip 5/ sunu +:8rlpt6vdj the ratio of highest to lownv c5rnu/0t9p l ::je qs,6up tud8is+est 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 length of9 7oins yhr99g j1s ar4v1:2g7aweiok the vibrating portion is 32 cm, and 7y9rhon arg 19gsevo9i2is4 aw7k1j :it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and fi2s;ih-reit4m zno a 1/rst three audible overtones in/1;o2z mi-t4ase h rif 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 freq 8hid rus a-dhs)2wpg8h420vcuency would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closr42-8s s)hvigchd 0haup8d2w ed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe org6sebf;ofh6 f7u0 t 1 y8kn)c(zx,am muan with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pifmf7kes6 n8byt(zh x1 umu0ac 6o ,);fpes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmonl1yp .qdg 0a1vic. What will be its fundamental frequency if it is fingered at a leng1l v0pgya 1.qdth of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E abovp ib ar8*c5sag;p;qs(e middle C (330 Hz)sc rb*a8;sg5pp a(;iq.
(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 midd*kjnj) ess.p:j4 syu+ le C (262 Hz) when the yn+k :ss j).j*4 uepjstemperature 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 2nrbu4 d* gz.h00 $^{\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 12–10(2k su9mw:;d hxbeo h8 should the hole be that must be uncovered to play D above middle C at 294 Hzk; h:sdub(2oeh 9mw8x?    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 eg*tp y-,r/ t (sfxia4can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is t- pfrixty/s(a*,ge4 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 bot+yec57hg8n.t s v a ;)mmg,kqyh ends. It resonates at two successive harmonics of frequencies 275 Hz and 330 8m+g hc,qy.e gn ysm vta;)75kHz. 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 evt 1, -bfyamjh+c(6,. wl edd$^{\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 withb: (xo4 y,6lbicxr+rl 8zf 5dmin the audible range for a 2.14-m-long organ pipe:ibr 6od x8r zl4y bfm+,5(lcx at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximates7lf:x- ng+ du-a u/btly 2.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (idabl7/us -tfux +g-:nn 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 t3fzkt 06lm3qcwcy7t -wo strings, one of which is sounding 440 Hz. How far off in fry 6 k 03q7wzfmt3lctc-equency is the other string? ±    Hz

  What is the beat freque(9hn * slgkt9iav ,o(xncy if middle C (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while anotheloqia2t7ty 16 0oz *zcr (brand X) operates at an unknown freqq 60*al itoc7ozyz21 tuency. If neither whistle 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 rr9y7)qmt gnu 6ct)a 7beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibratiy )a7gr tt76)nucrmq9onal frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hzg/ tjpi cvpa*x)h* g/ub;6fw -. The tension in one string is then decreased by 2.0%. What will be the beat frequenc btgu*w;ip6j v *c)//h ap-fgxy 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 hbw)sd: kc9tn:x1m6e try to play middle C (262 Hz), but one is at 5.0°C 1x:6 c )k9mstnd:ewhb and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Foht5k h n4kds0g9*w tu)rk B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequenc50h)knd9 s4*ghktu wty 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 1.8mhc 6mro(;thdc4 aj;un+b 92g- c0kmq0 m apart. A person stands 3.00 m from one speaker and 3.50 m frqjdcmucbgkon4ath2m9c (h;0 ;+ rm6 -om the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating at 132 Hz, but a piaix( dh6q ;aaa3no 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 oax;3d(haq6ia ther ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound of wavelengths 2.64 m and 2.76 m in air. How aexjg:9,zz*s r;j c7mmany beats per second j ,j;m sec79g:arx *zzwill be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequt04,s zvn 6fcfency of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with4 ,0c fftvszn6 a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequloje du1fu)a:stkr4)8j jrg)d5feuz a--. o :ency do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of rgt d j:z)d1 fo-k e 4us-:uarfj)j) .ola58eu32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source isi p ,-.bgu 1pxsov4 sfum+7hb1 moving toward you at 15 m/s versus you moving toward it at , v.o 4huugss1+ -i7 pmbxp1fb15 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 withpfr st/qzbdtm667 jx+ 29wy4 b the same single frequency horn. When one is at rest and the other is moving toward the first at 15 zx/rw2dbp6+s 9mj q74 tb6yf tm/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz/to.gqi1l 5u ;sw zy6q and receives them returned from an object moving directly away from it at 25 m/s What u lzg;/s61w.ot5 yqiqis the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a walddk jzi39oni-n1aup 8 q1(gp *l at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflec-nd*81njopuik3d1i(9apqz g ted wave?    $ \times10^{4}$ Hz

  In one of the original Doppler expht9ssj czn 4smk ,ud.3q:86e feriments, a tuba was played on a moving flat train car at a frequency of 75 Hz,6n skdf89qz u 4h .t3cmj:ses, 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 ultrasound ewgog;s . 8 yzk7yc gp1jl6 0zd+hwz4;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 1ohjg;+. dez7sg l kp8cgz 64 z;yw0wym/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 ultrasonic wa lg v1v7*rqnx .i0hi5 ifmgr-*ves 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 52bs5lze-mqen m3 ,a4 q70 Hz. When the wind velocity is 12 m/s from the north, what frequency will observerq5qe-bem24 ,3z lmas ns 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 20 9se ufi1 e s-ll,:y8.vejg(j*lwboa .$^{\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 c8v/lpwys+k9)il. by 310 m/s (a) What is the angle the shock wave makes with the direction of the airplankw.y9l/8vbl+ pi ycs)e’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 ofp *y6e *u-x vag3t8wwi a planet where the speed of sound is ot vi83x6*uw e-py *gawnly about 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 strikesd sxw;+-yze: e the ocean. Determine the shock wave angle it produew-yds;zex : +ces
(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 s d9sybtkk810jn 3 im.$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a plane exactly 1.5 km above the groundqyg5 nr2g3 1ks)cz gy2 flying faster than the speed of sound. By thn2syr qkgy52 z3g)1cg e 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 son -vh m5vvje+a3ar device that sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it -v+a5e3vm jvh 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 tq +:uvjraklo ,n+. mh4he human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists of jg/.xkdmfs* h2 r1 t7tmany frd*k7h2mx 1t.tj sg/ plastic 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 fr4*nz- uxy jn 5zxwj22vom a person makes a sound close to the threshold of human hearinz n2j u-xvxy2znw5*4j g (0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when 79l9t)fsz d;o im6 5sv gsuwpv.r 5io+an 82-dB sound and an 87-dB sound are hea pl5ivv6g tf m ;s+)9zrosio75u9 w.sdrd simultaneously?    dB

  The sound level 12.0 m fr3.o:zo 9e w jurr/cwo2om a loudspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the ow 2:e 9r3 ro/o.cuwzjspeaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 15q)ap8y- iakskc9.53qech;re 0 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is th.aeeqk h)-rpcyci53a 9sq 8; ke power output in watts at 15 kHz?    dB

  Workers around jet airzb g pq jm f)dyz)qgr0wtw550d8+ot6.craft typically wear protective devices over their ears. Assume that the sou 6jb q5).fwg zw0ttr8doq05+dmyp) zgnd 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 communicatinf 43v)dq+j* foo0ii ions systems, the gain, $\beta$ in decibels is defined as
$\beta$ = 10log($\frac{P_{out}}{P_{in}}$)
where $P_{in}$ is the power input to the system and $P_{out}$ is the power output. A particular stereo amplifier puts out 100 W of power for an input of 1 mW. What is its gain in dB?   dB

  Each string on a violin is tuned to a :vf)/q wec.0k4 f, m dktok+bnfrequency 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 violioqbg ; j8yxke ;,)hk1mby4 --vnv mn(yn is 32 cm long between fixed points with a fundamental frequency of 440 Hz and a mass perv;b1, yoye-yj(k)-x4nqg8n hm;kb vm unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration above a vertical open tube filled wi g.ez653 ma*rirb k.p8y9vavdth 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 again at 0.395 m. What is the frequency of the tunk5db. ryzvv6ar*3e. p g mia89ing fork?   Hz

  A 75-cm-long guitar s e(l)yea.g:k yhp/*uc tring of mass 2.10 g is near a tube that is open at one end and also 75 cm long. How much tension should be in the string if it is to produce resonance (in its fundamental mode) with the third harmog/(. hc)p*uk le ay:eynic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observedcvjn.q i7 6 knr,z6 cap/t07we to resonate as one full loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz ranh:fqn6m 60acqge 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 minq0ahm6cq:fn6 imal 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. zjmkj;hs* wh w(4yfl.7g3a/hOne train is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequel;fjwghh*my k4zwj.ah37 / (sncy 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 Hz5/xnr0c m)e c+g*d nan. After it passes you, its frequency is measured as 486 Hz. How fast was the tr gn n)n5d+xcea/c m*0rain moving (assume constant velocity)?    m/s

  At a race track, you yhy. e14 ,wapecan estimate the speed of cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose t.1h4,aeeyyw p he 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, ;7fpx6q72e(yd ra s hh 1z:qissounding together, produce a beat frequency of 11 Hz. The shorter one is 2.40 m long. How long i1:spr7 2az(yd e qs6hxiqh f7;s the other?    m

Two loudspeakers are at opposite ends of tl28 2 im4kfws0a.xqh-nt k :sa railroad car as it moves past 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 the car, (b) he is between the speaker-. 2wmsi4t tqn:fh klxaks2 08s, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in t4u tc6 zxkc8dbvxre5n:p 2k5;he 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 the red blood cells? Assume that the waves travel with a speed of84ebd:tzk ; 5xrxn2c5cp6vku $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/ g +k9+cakcq/oz zvjpi;m 2ul2g0u+6 js while the moth is flying toward the bat at speed 5 m/s The bat emits a soujuz22 ig +p gzj9c q+v06uokl/c+k;amnd 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 it g:4*f zdh 4hmiapproaches a moth. The pulses are approximately 70.0hh4 gzfd 4i*:m 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 before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signals fr typxd9f ufg 6 g/e2eof0,9k:hom 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 alp kdt9:u0h g 96f2/ge fe,poyfxenhorn 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 the vht-s c8kwqd qdje+78e78v; s presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider +eddc tq8 k;qe8s7sj87 hvvw-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,” m8rcutn4 zo)i:1 t,c.tcm3we 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 practit18ioctce m,n4u)c wz3 m.rt: ce, 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 fre.szqh )ww9jco(gs f( ,quency of about 1000 Hz is (sq fh)cj 9.sz(gwow, $I_0$ = $1 \times10^{12 } W / m^2$ 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 sl -n:24.hl lsam3nvgr 5m oe-oonic boom 1.5 min after the 24-lh. annv omgrs :-m53leo lplane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedbmn9)m4tn hv5(l bb(zv oat is 15 $^{\circ} $ in a lake where the speed of the water wave is 2.2 km/h What is the speed of the boat?    km/h