What is the evidence that sound travels as a w, s22bmn w2el ow:vq4cave?

What is the evidence that sound is a:(gmrb fy) o*awne6eue +1s4u form of energy?

Children sometimes play with a homemade “telephone” by attachingydx;) zl+y yn *:ohmh9 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 tryxl n y;yho9m )+z*dh:avels from one cup to the other.

When a sound wave passes from air inupn ;*q,:sd5pfs wpfk-8 5py z4g1jouto water, do you expect the frequency or wavelengwnuq*,s 8df 5j;p5:gy1- 4kpfz sopputh to change?

What evidence can you give that the speed of sound in air does c/r+xmgw)x: w not depend significantly on frequencm+ :/)wwxxcr gy?

The voice of a person who has inhaled helium a+lq3qpi5hbij4ui0./ ,pkwn sounds very high-pitched. Why?

How will the air temperature in a room affect the ssdean)d/an;r865dx -ml n(qpitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude ofbt elnq o02r+gl0wj-/ sounds in various frequency rangebtno g-+w2elrjl q0/ 0s. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced clo mp-(vyku+ag/ ,ok h;4 yku(cyser together as you move up the fingerboup;c4 k y-k mgv(k(,+ oyayhu/ard toward the bridge?

A noisy truck approaches you from behind a building. Initially ue hw9/igxw-3 you hear it but cannot see it. When it emerges u-9 gxww3/ hieand you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whereas bebio nvn/u.7bsf 97 3iyats can be said to be due to “interferencs7buo97i/y vf3i .bn ne in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered,2o4jgsxw:6zb pqpcjq;0 1-fc would the points D and C (where destructive and constructive interference occur) mo- fqgjxws 0 zobcp246qpj: 1c;ve farther apart or closer together?

Traditional methods of prot t-6 , ux)fmaskvvc.o(fo5r:secting 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 headphones in addition to the ambient noise. How could adding more noise res:a, tou(vr.smfc) 56v- foxkduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought of as a*zxgfc6*unqci0f h7 4pb*il; superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a)*ip* fzgn uf c6lb4xq0hi;*c7 or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if w1f-pgw a.u9u0e vq r7by co7-y.cfr. the source and observer move in the same direction, with thfy 1c9p0 c wuuwe 7-ry a7vgqor..bf-.e same velocity? Explain.

If a wind is blowing, will this alter the freru23ty07)k ugv3a fp zquency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocity chang y0)up 733u rtgkfaz2ved?

Figure 12–32 shows various positions of a child in motion on aw -)a h8p+afdkljx-x7 swing. A monitor is blowing a whistle in front j l7+)pax-- hdw8kxfa 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 echo of w8i/r :mav b)wfn( 8vther shout reflected by a cliff at the far end of the lake. She hears the echwft(b/ vwriv )a8:8n mo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just bep+5 by: dnx8bklow the waterline. He hears the echo of thd+p yn5xkb :8be sound 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 wave jbt59:ntcwp; lengths 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 scj; 038 gy1vb7yxbmh3gf+cl nhl 1xr,bhool of tuna on a foggy day. Without warning, an engine backfire occurs o1glhm8bc0rbvf7n g +b3yyhjx,1 l ; 3xn 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 clij /as cb bh1,ek0a4w+xff. The splash it makes when striking the water below is heard 3a+ kacs4hw1xb/je ,0 b.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees m;*l sj1,sweey w02rn 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, wm 0w1jly*2nsse, r ;eand 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 o 1p6ce sb*ca t mt-.d1me7j0vrver one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (a760c. dc e-m1rsmeb1va t*jtp) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the g- k6ln.qrr* o;lz 4wzg3)x4t. zanrqf5 ysm: 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 inxmy scl19)8ioi;v..jg w g5tytensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95kkrw3ws ne;- izi7*)w dB when fired simultaneously at a certain place, what wi;wswkr3iw)- nzki *e7ll be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane wi f b.dyq3u*,z* x-4n(gfmeu;y b5fkjx th 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 intensiti5xg*zb ffqjy*n u, m4-yxd;ub k(.3fees, not dB’s.]    dB

  A cassette player is said to have a signaxl*lx cm-i* ke +-4blgl-to-noise ratio of 58 dB, whereas for a CD player g-lexik + 4cl**xbm -lit 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 o hbe5ub;:wv *chm -z)in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a o )c-; :z*bhwhmv5ebusphere 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 zsdxhejirvg ( 4n26+; 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 m0 bcyi*(q cb,lodest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from(0c qbyi c*,lb 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 2.8 m i ;bkkf8r (fu+rj0 f;evn front of a loudspeake 8fuf brk; r(v+f0kj;er 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 c10jwwm9x6jb of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amoujjx1b0ww c96 mnt? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factowb );ix0ooz+; ycf*q xr will the intensity increase? Increase bfi) xz;o yb;oxq0 c+*wy a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but obnh.4l+c9mv-gyxrl f 5 p fm/6ne has twice the frequency of the other. What is the ra4fnm l ybr6cm9gl.+- fp hv5x/tio of their intensities?   

  What would be the sound level (in dB) of a s zyzc.;j 3l7khound wave in air that corresponds to a displacement amplitude of vibrating airy. z3hc klj;7z molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as lom(/d cp8w 4d) a,t:lcu v7csequd as a 100-Hz tone that has a 5 : dc4(m8p7sdtaq ec,/vu)lc w0-dB sound level? (See Fig. 12–6.)    dB

What are the lowest e76fr.b* jhpyfd5 tlas 3 6bv:and highest frequencies that an ear can detect when the sound lsj:avf6fy hp75b r6.tdble* 3evel is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sou czz k8/n8n lz;u6gy*und levels. What is the ratio of highest to lcn86*gunz/;zy8klzu owest 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 s77xafxmxo( c: g5s,hof the vibm7ahs:xcs, x x7g fo(5rating portion is 32 cm, and 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 fundamental7 5;q6 y0c:trl evnvqu and first three audible overtones if the pipe is 5;0 uq7vtecqnyl6v :r
(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 expeckm-pqv5r5jccrm2 aha.9 g es3 2z3 +xwt from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tube? 5h5q2 sc.ev9-zrmwj3a +kp2 mrx g3ac    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 sij2 )ecn 0cxq dm6p1:;bl5 mvapanning the range of human hearing (20 Hz to 20 kHz), what would be the range of :eac6pv ;)1mb dim502j cxlnqthe lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string han41vfj3km f1 1uvdgg..ha5 xrs a frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fing.n mr1adv1vkx 1f g. g5fu43hjered at a length of only 60% of its original length?   Hz

  An unfingered guitar stre0tb1oimsg+ 9 ing is 0.73 m long and is tuned to play E above middle C (e +i 0os9bgm1t330 Hz).
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that emits middle C (262bqfakw;n agr 191-x r7 Hz) when thk-fr1na1w9r abgq ; x7e temperature 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 ai u 6qhbc gf,l- znr(6jq;zqf(tx64+g t 20 $^{\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 should the hole be g3sr j97g 1.g x8yrig/ mbu zghe*0pp2that must be uncovered to play D above middle C at 294 Hz?gg.9xjghipuyzg 1*rr e78 0 p2/3sgmb    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,(ax b1n -9nqpmmzb:7i and 616 Hz, but not at any otherpnz-ibm a:9qb 71mxn( frequencies in between. (a) Show why this is an open or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at both ends. It resonat3q7xpto m2gd*es at two successive harmonics of frequencies 275 xq27gopdt * m3Hz 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 v05ajh0 2s ybt(wy-zfr8jwp *$^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are present within the audible range for a-hnicvl- l2z 0wvgr ;0 2.14-m-long organ pir lw0-;02 v czlgni-hvpe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long)g1ja2l s6idt . It is open to the outside and is closed at the other end by the g26 1)dlisajteardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to adjust two strings, one n mpx813oggy;of which is sounding 440 Hz. How far off in frequency is the other strinx3ypm1 o;gng8g? ±    Hz

  What is the beat frequency if middle C (262 Hz)492 hekg:stjb and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while another (br9;bjm fxy5ja.and X) operates at an unknown frequency. If neither whistle cayjm5ab j9x;f .n 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 beats/s when sounded with a 350-Hzl:9ltd0w1 gqhe sw3 f; tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your lf0t hl39g:s;qe w1wdreasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tensi26 rnhp hbc x.:4yb5vpon 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 E5x6nvrp2 y:hp c .4bhbq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each 174 vmd)r zp:ysl df-htry to play middle C (262 Hz), but one is at 5.0°C and the o s4mv:py) d-lfhzr 1d7ther at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A,c p(,by 6p2)dzpq.tjl B, and C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible fre2t)j( z lppcqp6.dy,b quencies 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 speia :(uqg*fagbl2 . e5vaker and 3*.:agi5f u 2(bqaelg v.50 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 supd;xn8*;p w :t, eyukwuposed to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when *n; w,:udwxetu8;yk p 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 msktb83i : j7l.brdc r/.pl (co and 2.76 m in air. How many beats per second will be hk ( .7.jc l3bric8sbdo/tpl :reard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency o;8r9sdm;p( wmtq y hun; 9g,pmf a certain fire engine’s siren is 1550 Hz when at rest. What frequency do mwt; sd m 9;mp,gnp(;r8qhu9y you detect if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequvsl 74q j s;bg6/k2np1 d ,lxxtf5; wvn05axhyency do you detect if a fire engine whose siren emits at 1550 Hz moves a0x1l , lbxk v 5th ;6j5qywpx sa/7ds;nngf24vt a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving toward y.6sdpw it+k:q ou at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they clos dstk:pq6.+wie? $f'_{source\,movine}$    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 7 ( pf3rjd:om 6scurm7hbq4y*ed 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 bpf:63rrc dyjm4u7(hs*mq o 7 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 50m8ot4 )uo.3zq )hollo.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is tou)o 34olm .loz t)qh8he received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of u i7f,rg7dl-qcj1:bp5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz.r177gd b ,qp- fi:uljc What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experimwtl(lla*qv j;*gjr 3yj6 29vcents, a 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 6ql;j9jw l3(vg c*avtrylj*2heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blotya(m0: 2;62jfdr, wcpb iuk lod-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 6bm :p(uklwjc2f 0t y2,i;darfrom the sound source?   Hz

  The Doppler effect using ultrasonicn+gbzs qq*(8c 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 emqe / bo.xe+oy6its sound of frequency 570 Hz. When the wind velocity is 12 m/so+6xe eyqo. b/ from 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 its sp g9cyza72e;dceed 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 2.3znwdpx u8wv-:g4,d vz-o k w18 where the speed of sound is 310 m/s (a) What is the anwv:,k d nzd gwwp 1x8-48-uvzogle the shock wave makes 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 soap9o1gnm7,qs und is only about 35 m/s m q,9oasngp17
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s strikes the ocean. Deter/e3 9 b)atwggumine the shock wave angle it prg / be3g)9wuatoduces
(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 hz3j 99r jbd/ )jspb3mc99n4p9i owqb$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead ane7n*qq84/hi br 6qsh hd see 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 horizontal distance of 2.0 km. See *ehs7qqibh4/ n86qrhFig. 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 dd8/jb bi*f)sk0y mzz/evice that sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth ford8b0m/kzijyf/)*b z s 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 h+ 8vyag(nmx)in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It 0 iqqy(-) qxi6b0bfe q:gq,eajx b2 y+consists of many plastic pipes jexq0qx q6eai)f i- b 2, bygbyq+0q(:of various lengths, which are open on both ends.
(a) If the pipes have lengths of 3.0 m, 2.5 m, 2.0 m, 1.5 m and 1.0 m, what frequencies will be heard by a visitor’s ear placed near the ends of the pipes?
$f_{3.0}$ =    Hz
$f_{2.5}$ =    Hz
$f_{2.0}$ =    Hz
$f_{1.5}$ $\approx$    Hz (Round to the nearest integer)
$f_{1.0}$ $\approx$    Hz (Round to the nearest integer)
(b) Why does this display work better on a noisy day than on a quiet day?

  A single mosquito 5.0 m from a person makes a sound close to the threshold zhas1ef7vw0f c /,8jp of human hearing (0 dB). What will be the s7wvjf/ fzp, 1hec0as 8ound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-dB sound are h fu*/ysi iw*0ujl(x- aea0u/uxs* y(f*wl-aii jrd simultaneously?    dB

  The sound level 12.0 m 3ln. :nlqsj0u from a loudspeaker, placed in the open, is 105 dB. What is the acos: unl.0j qnl3ustic power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output a xyn 9cq84c7 d*gzj bbjp7q32rt 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power output8 zj4 3qnyqcr779j x2b* dcbgp in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices get pg,qrs 94:over their 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 cm. What would be the power intercepted by an unprots9q eg4tg ,:rpected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, the gal2j w 3m9)rn*zcugm54/sikk jin, $\beta$ 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 paz cfh.9:/r tfrequency 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 with a fundamentuk,jpao6in3v;b oc1 *ne4q4l al frequency of 440 Hz and a mass per oonpjkvq4n li;1eu* 6,a3c4bunit 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 3wed z* y*6h0 surnq8twith water (Fig. 12–35). The water level is allowed to drop slowly. As 6 hd*rwnys8qzeu*30tit 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 a tube thaiyawtc2( pv31 t 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 harmonic in the tu (c ayv13itpw2be?    $ \times10^{ 2}$ N

A highway overpass was observed to res*:1 / ovruml2txr i3 wiv.8rmconate 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 com :2(pu8u( , vswo4e3cipiovm ring 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 other. What is the frequency of4rp3epm i c8:, 2uwi uo((vvso the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. T:+ 6 orend+q ncwpgl..he conductor on the stationary train hears a 3.0-Hz becdn.r.+ wl6gnpe qo: +at 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. Af5-ph/t j yzb8oter it passes you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant y-bt8jz p/ 5hovelocity)?    m/s

  At a race track, you can estimate the speed of cars just by listeninbza;w vyq1g3i(dqcz()(q 5twjh bs 7w gw34e6 g to the difference in pitch of the eb1((7ah gq z)qwwtj swb34w6d vge3(i c 5;yzqngine 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, sound/g(t-h j 7ngeene+;aving together, produce a beat frequency of 11 Hz. The shortera7nj- ;vt(ee ehn/gg+ one is 2.40 m long. How long is the other?    m

Two loudspeakers are at hi / -sn485esiknmk:gi* j+zl opposite ends of a 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 observiis:si/nje l8 *g-mk5hkz +n4 er when (a) he listens from the position A, in front of the car, (b) he is between the speakers, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in the aorta is normally about 0.32 m/s what beat awehpv3l b, y+.hq(z5frequency 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 hyh .lp azq5b e3(v,w+of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.9u o8f oee5w( z-k6s)pcok*fz5 m/s while the moth is flying toward 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 u )oe98skco56(fpzwf o z-*keoff the moth?    kHz

  A bat emits a series of high frequency sound pulses zjrw;( aw+le ,z(j ms9as 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, a+zzmjl(( ejrsww9; from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to sen u8m4ij;)m6x d*tjt7cf 0qzjo7)f oiwd 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 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 j8i4j7mdx t)u 0czi 6*) joffwmq7t;otube.

  Room acoustics for stereo listening can fl m -,gyq1tbjsg6t6: be compromised by 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, and 2.8 m high. Calculate the fundamental frequencies for the standing waves in this r , 1l6fts- g6jbyq:gtmoom.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” ir0eapqt1 jk67,y/(ql6ul u vonvolves a long, slender aluminum rod held in the hand near the rod’s midpo6e,6yaqqul/tu1 0vkj p( l7orint. 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 thresh:sz1m4z g lz8zc apx44old of hearing for the human ear at a frequency of about 1000cx:p4m1z 8g zl4a4 zsz 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 obe ma1n s4f3es2server on the ground hears the sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s altitude?es3nfs mea124    $ \times10^{4 }$ m

  The wake of a speedboat is:nw8y 0/kmg y +yf8u.jkv;tu w 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