What is the evidence th /8.oa9ubskd dat sound travels as a wave?

What is the evidence thatqeci- md k e.s3;o5o)l sound is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a string (o, fp31sol9osk eg4kc m.n z)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 travels from one cklcn .s(ko m3oo 4fez19p ),sgup to the other.

When a sound wave passes from air into wamkoh2z58 gavmsbui40u3)dc 9 ter, do you expect the frequency or wavelength to change?4uch)0u8z sm5k 3io ad29 bvgm

What evidence can you give that the speed of sou *3;qbqm h(eound in air does not depend significantly on fu(qo;eb m3hq *requency?

The voice of a person who has inh8 dwqd f:;v8fealed helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of organ hglh9qattz2ugv)ldj1 ip ; :5v+9 ;agpipes?

Explain how a tube might be ,(g u.jo i.wula;4j; bs/ridbused as a filter to reduce the amplitude of sounds in iw;.su,4(;irodgjb/ l .ubja various frequency ranges. (An example is a car muffler.)

Why are the frets on a gub :w6 qxd5v/ozitar (Fig. 12–30) spaced closer together as you move up the fingerboard toward the brixvqbz: dwo56/dge?

A noisy truck approaches you from behind aiu2n37r*i8ljn v d7 lg building. Initially 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-frequel7ni*j3rui n87v g 2ldncy noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “inteqx(3 bqzlw5x2 rference in space,” whereas beats can be said to be due to “interference in tim lqwz3x2qxb(5 e.” Explain.

In Fig. 12–16, if the frequencxw6q t )aui*j;/7( e)trjc1 b5inoni my of the speakers were lowered, would the points D and C (where destructive and constructive interj*enqn1 ia;tb 5c())7/mroix tw 6uijference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who work in areas w-pq:m ry eni9-ith very high noise levels have consisted mainly of efforts to block or reduce noise levels. With yir p-9q:-en ma 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 reduce the sound levels reaching the ears?

Consider the two waves sho 2a q*f+8xfwjywn in Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frff a8y2*xw j+qequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and obse /n 7hr9 (ic7nwdg.zymrver move in the same direction, with the same velocity? Er/7z gcn9y7 w(mdi nh.xplain.

If a wind is blowing, will this alter the frequencysn8 7a*f ) fyy47djj)sw5xwv hh;yi 6s*q0eag of the sound heard by a person at rest with respect to the soyyd*n)qyhaesiswxff6 *jhs7v5gw4 0 8 )j;7aurce? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monitkd n b z8()ms*mf12cxlor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear the h*8)f( m k czmsldx2bn1ighest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening 9*xv4zlv /qk5vnco)v for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo nc 4kq*vv/)xvlvo59 z2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the;ucsq4 y/ntg y+ei0bid;p0v(0i p we5 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 speed of sound in seawater is 1560 m/s (Table 12–1) and does not iv;y ey d0ist5ep q(cpi4w0bu+/0;ngvary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the waeq6 rv5cpwg22 velengths 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 re3 2 ykkgo/ g;a;hme*school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How mucm3;e kok/h;* gye rg2ah time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped fro*rdkhs:r :nk iah+y emge) */v.1uh5l m the top of a cliff. The splash it makes when striking the water below is heard 3.:el:as n+hhhg*v*5im.1 d)ku/ ry ker 5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stonu2uy e60 mnkp+e 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,yme06kn+u p2 u 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 over one mile of distan nb0q(r(ezji - ss,qw3ce by the “5-second rule” for estimating the distance from a lightning strike if the temperatu,3 (sqnjzqib( rs0e-wre is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity sn/ o0g hjpr-9,hrt 9uof a sound at the pain level of 120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of a sound whose int /u17,u qbjslwensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when rh54th djtcz gkkg/ 9o6a0s.i 8*vd2:mt*oacfired simultaneously at a certain place, what will bi tct oshd.8h :/0g m9gk*kcvo5a*6 zra42jdte the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane w ph9b(8yd6,e jojs(dxith four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this perso e9bod(x yj6p sdj(h8,n experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to ha :p43jp:jrf2 qqt 8lzxn*hk n9ve a signal-to-noise ratio of 58 dB, whereas for a CD player i hj tp n348z9kqp xrj*:qfln:2t 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 pers i-.c3q8et2x 1kvds abon speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphkcbeai32.-qs1 x td8vere centered on the mouth. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave strikes an eardrum whose area is oubdan,js ( 20$5 \times10^{ -5} m^2$ (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 vpq fizj i:001more modest amplifier B is rated at 40 W. (a) Estimate the sound lpi 00z: j1vqifevel in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registered 130 dB when placed 2.8 m in front of/-x yze wehbih 3dn)+ fi7,gq4 a loudspeaker on b,-4+iedi 3 zw)fn7 hxghe/yq 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 7j ou;y)9,2p0 kftlf uiyoy+ pdifference in sound level of 2.0 dB. What is the ratio of the amplitude2pof)yl ;op0ykt+9 , ju7ifuys of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by msu,9 2nzz7xoav y f2i m;z k0g)ld-y*what factor will the intensity increase?0 z*7n s-ymx,)io az 9u dg2;yvzmfkl2 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 t8 s0smxb -6vnbr w,v1aho2jr.wice the frequency hbarvx sro ,28jw16.0svnm-b of the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in ;f ,(:bx zf fxe40xaurair that corresponds to a displacement amplitude of vibrating air molecules of 0.13 0r4 (fafux: fx,bx ez;mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound leve.r ev:,u/.ddwr + 4dmirto w5jl to seem as loud as a 100-Hz tone that has a 50-dB sound lee4tdr+j w5rv.u did,.rw/ :movel? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when ;f mrsj)(yj8o the sound level fjs8 rj)(o;my is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound g4t fqa8fbcpx ock49)v/o.6v levels. What is the ratio .49tq afop )g4v6kxbfv8/cc o of highest to lowest intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental frequencyn-jino- ( y7ep of 440 Hz. The length of the vibrating portion is 32 cy-enpj-(n oi 7m, 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 fundamental and first thnct mp):v* kc7ree audible overtones if the pipt7) kvpcnm *:ce is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you expect from blowing across 73mn:x :3g mfjh 4iw+yjkn*yq the top of an empty soda bottlxj+k3g7nhn q ymfy43m:* j:iwe that is 18 cm deep, if you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pipes spanning the ra:vrq) vcpzu 2 rv.,,honge of human hearing (20 Hz to 20 kHz), what would be the ra ,)c:ohvr2 puzvv, .qrnge of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its th.om2 m6c2p b6z3-hhwl rvt7kbaykh: n2f7o k+ird harmonic. What will be its fundamental frequency if it is fingered at a length of only nyohtz2 hmk +7b2fvmlc6 b726r.k- 3k oh:awp60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E above middle 4sd8nh s4bhp1 C (330 Hz)bs h4n4hs1 p8d.
(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 miyd3q/+pfhc 1addle C (262 Hz) when the temperatur1 +cdaf3y hpq/e 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 o3+upr o1t -lhq)f2m j20 $^{\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 bz0e zg875jyq xe that must be jz5g8xq7 yz0euncovered to play D above middle C at 294 Hz?    m

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

  A particular organ pipe can resonate at 264 Hz, 440 Hz, and 616 Hz, byw87iaqkscj )ojb x(s0rp -:.ut not at any other yj. xcw0oqb- jasp 7rk 8i(s:)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. e.*fof m6 obri2n so-)It resonates at two successive harmonics of frequencies 275 Hz and 330 Hz. What2 en.bo*ooffi srm -6) 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 d-p aai o:-e4f$^{\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 presentz.fw7q)y( 2i ws4oyaw within the audible range for a 2.14-m-long organ pipe at 2w)7q2wyosyz 4(. waif0 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It whixi b7ke j 3h..had7i+f4/ais open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canhi4jh7h3x abwei.7+ .f id/akal. 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 qye9(y hdxz.(2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency iq(zy(d 9hx. eys the other string? ±    Hz

  What is the beat freo 63:cv-i1b(ompv4pffu * afw quency 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 another (brand jhaxy4j4y; fcp6-px -X) operates at an unknown frequency. 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 opp-fj6-y j4ayxpc4xh;erating frequency of brand X.    kHz

  A guitar string produces 4 beats/s whef * r *l6-uhp x3(gkmukdlls4-n sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Exlm hugl (sldr*k* u436 kp--fxplain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. Tl:nx+2fp/shd l m 0kda xn ux2:wre7.1he tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are plk d2n:1x/2sxe lnru .0f px+7lwmh:daayed together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard ihd1fk(jx znu1h34t8v llp02 jf two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other a j8ptd 0z xj(n1u4l2lfv31h hkt 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Hz; f3x36h j qt fxiaibq,86bb2a(when A and B are sounded together, a beat frequency of 3 Hz is heib2q6xf ta q6fixa3b3bh ,8j(ard. 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 sta; 5fvvsv2vlj/7 ul8wands 3.00 m from one speaker and 3.87vl 5vj;lu a2f/sv wv50 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 suppos+y69my5i 0gl:uzwm dsed to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vi0dm yuw:mslyig 9 6z+5brating 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 and 2.764 zixig3j+yr+ m in air. How many beats per second will be heardx++4 gi3iyzj r? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certai9jqy7*(vys +tsk0 jde v uql;,n fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you movy0j*v ysu+;e(9stjlqdvq k, 7 e with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect i,kpso-m 1wkw1 f a fire engine whose siren emits at 15k ,-1msowkw1 p50 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source i u.sb)b;/7+ tflr ug0f)hulkas moving toward you at 15 m/s versus you movinu+0btf)rf )a.ubh sul/;7 lkgg toward it at 15 m/s Are the two frequencies exactly the same? Are they close? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped wixt 9x5n*yo2s mth 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 the horns emit? Assummy n 2*9o5sxxte T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves ch1*qn:6ili aat 50.0 kHz and receives them returned from anc6l iah:n*i1q object moving directly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it )g :aj/(ao uhuf7t9s4aulac* fo; z8fflies, the bat emits an ultrasonic sound wave with fr)*a8csu(h/ 4jgfoz:uaot; f7a 9alf uequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was2+ i:1 mv+2mfe fejyrc 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 s1ymr jm: +ce+2fvef2itation. 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 waves t dvi+o2o:y -gto measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from tgti: +2 yvodo-he sound source?   Hz

  The Doppler effect using ultrasonic w(eahcl 7m1, cdaves 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 of1fu (qd rd + gaxq:x0be*;1ofh frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who ar+e x 1;b g:dor(h0fauq q*1dxfe 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 eafm a.75g-qhp2;oth at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where the speed of sound is 3quj/b1v u1s3o)hi4j. p ;uyoe10 m/s (a) What is the angle the shock wave makes4e1)upuo3boijh s1 y. u/;jqv 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 ofg1 bxgchm,:h; sound is o, :;cgghbxh m1nly 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 strikes the ocean. Detxz2e ng0lk;.termine the shock wave angle itg;.enkxzl 02t 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 a)xz b ehd)0amkgn; 60 :rwk;w$/theta$ 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 grounxm3rn 77jzrkq5n :9ned flying faster than the speed of sou797z 35njq:r ernkx mnnd. 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 that sends 20,000-Hz sound pulses downward c8h:bkr nkk wx7/7h*zfrom the bottom of the boat, and then detects echoes. If the mac*8z 7x kbk7hkh:n/rwximum 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 thek6, e n 1 9rmwkl:x.mb+msrnm0re in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a se3-.( ab z8ciyt/uw rrgwer pipe symphony. It consists of many plastic pipes of various lengths, which arrtcuy z(3 ag/wb8r.-i e 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 clo8hib +9, uk:qpl4cguo se to the threshold of human hearing (0 dB). What will be the sound level of 1000 such mosquito9hibu+ ocguq:lpk, 84es?    dB

  What is the resultant sound level when an 82-dB sound and an 3e)p w0* fyxm o *3fkar61;gpflg .laq87-dB sound are heardmq 6rp3o g.; f*0ak1)xgfa3lw*yl f ep simultaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed innw4yaeg-q filc 3,h ihq1: 19m the open, is 105 dB. What is the acoustic power output (W) of the speaker, assuming it radiates equallhlc11i: yn3,wi-4a 9qqghe mf y in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The power output dropudl)hx oca8:,qh-cvng e l+3 )s by 10 dB at 15 kHz. What is the power output in watts at 15 kHz?cd)o3 :)lvn +aulxq-8g ec,hh    dB

  Workers around jet aircraft typically wearhw7 fjko006ur protective devices 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 unprotected ear at a distance of 30 m from a jet airplane ej60rwu7 foh0 kngine?    W

  In audio and communications systems,yz kqljj2+i*v1 por; 0d;x3xg 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 violig.)wx x ew5n llkwt15ef7f-b; n is tuned to a frequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 3f1ycwo*.xx+.-gd z ;a iv8d xw2 cm long between fixed points with a fundamental frequency of 44y.ddw+cg wfa*xx izx;vo.8 - 10 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 vibration6d(k :0, yvmaemcn ik+ 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 forei+mc :v6kyn0akd( m,k 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 that is open0u 0+bc,(iwk.cosvlm at one end and also 75 cm long. Hob svk0m0u(c +.wcl,oi w much tension should be in the string if it is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one full loop (o-nwo1eid9zy4 mm). b $\frac{1}{2}\lambda$) 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 tonk q(he* p)o; yvp7b(tgbuz-u7e in the 500–1000-Hz range coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a poi p (vkho)u;e-yg7t*z puq(bb7nt 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The conductor on /a*.kn q lbk/ddjz iua8;-7 ygthe stationary train hears a 3.0-Hz beat frequency when the other train approaches. a;ky7nd8u zi*k q ./l bdja-/gWhat is the speed of the moving train?   m/s

  The frequency of a steam train wm4 vd.dups8zpub ;k7 o x:,r:dhistle as it approaches you is 538 Hz. After it passes ypu4;k.xpd:uz d bv,dom7 : 8rsou, its frequency is measured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed t4ca,- tvhu;9uwrn,n8 lig;j of cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops byv9t ,4;lnn8 ;c ughr,uwt-ija 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 11pa+/i ;o cg7z7de1,ktkxow(g Hz. The shorter one is 2.40 m long. How long is pg7z,1 w(dake+;xiot7kcg/othe other?    m

Two loudspeakers are at opposite ends otnb :s66d r6yjf 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 observer when (a) he listent 6j6:n6brsyds 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 whfi9pvk4 d2 +nyat beat frequency would you expect if 5.50-MHz ultrasound waves were directed alop94 vf+k2id nyng the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s while the moth is flying toward the dmy8 r+qdie9 8bat at speed 5 m/s The bat emits a semiyr+d8 9 q8dound 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 approaches a6,gdmp- nys j0f nhz8: moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emzh,jp n smgd0-8:6nfyitted?    m

The “alpenhorn” (Fig. 12–38) was 5t q37 lgdmi4za,hpx7once used to 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 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 xmip 4,g 7h5t dza7ql312–3.) Model as an open tube.

  Room acoustics for stereo listening can be compromis4 y++om 1lexkjed by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Considerlok + 4eym+xj1 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, cf se*,iasm9zp1 a,u;l;n5l a walled “singing rods,” involves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can blssa; 5*a,l1fa ;n mupz,we9ie 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 humaes;v/ 4rv3.p1c krjq dn ear at a frequency of about 10rdvk4 pr/;s c .q1j3ve00 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 os+1 )ib6,ye2fwa-mm fx1 irv vbserver on the ground hears the sonic boom 1.5 min after the plane passes directly overhead. What is the abi1m2sim yr6 -ev+) fw1,xvfplane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is n)krz6voo47l 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