What is the evidence that sound travels as a waven - 0r4lpr)aih.3rrdfh1 g9afgwg1 h5?

What is the evidence that sound is a form of enerw *zhf5fuk)qm1 8vk pll3nx4x .3p5oagy?

Children sometimes play with a homemade “telv sovxk1jomv+x 7(:b-ephone” 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 hearvkj17- m+vbxo s x:vo(d at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you expe1 qrmfi:;0xy w2 qs. (lua2mzxct the frequency or wavelengthmql0m2(i fr ;uyxz1: w.aqx2 s to change?

What evidence can you give that the speed of sound in air :v42e e2xglpv does not depend significantly: 2vpvg4x2l ee on frequency?

The voice of a person who has inhaledtf 9;(2oct, 5oo rn3ts:xmh x71hb ykd helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of organ pipes?8:zmj oji.+7kp uk; ht

Explain how a tube might be used aspm3vpf)- qgu)h -txy + a filter to reduce the amplitude of sounds in various frequenqg-h tyx3 ) mp)+vfup-cy ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) sqp 8)o2)-gf vdk)qh lqpaced closer together as you move up the fingerboard -d f lp8vkq)hqo)qg) 2toward the bridge?

A noisy truck approaches you from behind a h: e9 msc6gd1abuilding. 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-frequency noic 9h:das1egm6se. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in spaceqr 4.av) kex+.tuh)5z m+xg;ofi:uer,” whereas beats can be said to be due to “interference in time5 +..u)h4;+i:r tzevkf maoug )qrxex.” Explain.

In Fig. 12–16, if the r j3 51k8( 4lg; 7emwcmrenddbfrequency of the speakers were lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or closer tog4e5cjdl wbn re(1drkgm 78m3;ether?

Traditional methods of protecting the hearing of people who work in areas w c9/kr*vm9vymkbri6o 44u :jyith 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 addition4v64k9m/ rcm yi ykrbjvou 9*: to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fwb)yf7f)*ke qz 6xd k7ig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.*e) )qbfk xk6f77wzyd
(12-31)
(12-18)

Is there a Doppler shift if the source andy :nj .91aocgy observer move in the same direction, .yo19an yg:cjwith the same velocity? Explain.

If a wind is blowing,y*q 1z+cpd bqg6(,* jak qwrth0p,gu) will this alter the frequency of the sound heard by a person at rest with re, + w(hqp0jtqryqd*guck1 6 p)g*zba,spect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in moti uyh64s1hk)*uvoiv k5 on on a swing. A monitor is blowing a whistle in front v *k4h16iovuuy5 s) hkof 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 oxrc3qr);3uo l f a lake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate t rqru)c 3;olx3he length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline.fth:- s f6xub:u8hw s58b.iel 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 vary significantly with depth.uwbss.:fbihh6u-lf588e tx:    $ \times10^{ 3}$m

  (a) Calculate the wavf hgt.msv4m2l-v/kr 1/th - mqelengths 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 sch1gn9m me06 zp1oxd m)1azh 2j wmy(nc5ool of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.m9nm 2(5 11mp1y)n ze6zmgxjahod0wc0 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. The splash it makes wjq m0)gid*ka+0iv, x rhen striking the water below is heard 3.5 mi0*grk,i q+0 xaj )dvs later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the concrete0sucu :nirw ); pavement. A moment later two sounds are heard from the impact: one: cu)ir0;nsw u travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over onxw jr.n21)j ds0q /lx ar182k5pxg cbse mile of distance by the “5-second rule” for estimating the distance from a liqxx0xd)8l.srsgj12 5crbj2n ka / 1pwghtning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the h)j nrka-:9q7oz4intl x q /g,ma 81jhpain 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 in3n1 rg:v qq7s;y5mseu ;1t4ats mz ql;tensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce wwy 8 :f54jt1dxzq0uxa 4i:ipa sound level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is explodyua 45px1qwwjdxiti8:f:0 z4ed? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an vkn59s z2wq t:, hndxwub-8;m;7bif jairplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. 2j:v-t7 nbmik;bn ;8d9 wh wqz f5,usxWhat sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-trp0ji i07u3 qfo-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each devi0i j 0i3q7pufrce? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power bjg c/ dqk+5 2fobjy(7output of sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the moutd go2k7q/b(5j yj +fbch. $\approx$    $ \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 os;i;e5 bgno8whose 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 1s;r,ybn,s sgc/)ezb amplifier B is ratecr),bsns1yezb, / ;gsd at 40 W. (a) Estimate the sound level 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 platk*g*my2.(d0 s nch qjd+rr n6tk;o w4ced 2.8 m in front of a loudspeak*q ;s0jk4kmgdd2+ nowh.(tr6tnr*y cer 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 sf1 hc0t-m8ekt kf +y3vnkp ln: 1*1mafound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose level1ly1 pt*m-knef 3mtf8n c+kv:1ak fh0s differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the inte(dud. 40m (h;7uir rhe)lv rurnsity increase? Increase by a facmvd u)ri(uhru.7r(r;0hde 4 ltor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have eq2d qjja*:upl 2re ko:nmv.6p ,ual displacement amplitudes, but one has twice the frequency of the other. What is the ratio of the:rnu2, pdv6ke mjj*pl:2 .qo air intensities?   

  What would be the sound level (in d:, n5sq- 1p0 kbqe rogjd; ridsl008tpB) of a sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.1p g qo, s:- kn;rd5i 08e0sb1r0pjqdtl3 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as2p(;tu-gh/gxjj)lgwo gq v.6:)ka 3kc yu ,yr a 100-Hz tone that )au3 j-hco(:ggrpy qu gkwvk6,j) g2 l.;xt/yhas a 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencfsky /,qamh4s 8se))aies that an ear can detect when the sound level ism /a8he) k qyss4)f,as 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge r9t/) z+ql h8mdhqu0fn ange of sound levels. What is the ratio of highest to lowest inte9f l+)q08hqn/m dtzuh nsity 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 f;db2c zm+l) /ybf6ym tnzvc44undamental frequency of 440 Hz. The length of the vibrating portion is 32+y6t42cz 4yvlf dbbn) czm; /m 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 3kr drour 7np wnhyh,h;69t,+the fundamental and first three audible overtone nk7owrhyu +9,h,thr;3prn d 6s if 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 frequency would you expect from blowing across the top oay wi apn;rd d*ulqunsxy70+ 4y .6*sb;i7-cvf an empty soda bottle that is 18 cm deep, iau;al dy+.c4wv*7 usri q;di0n-p7 n*syy bx6f 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 opem;o5knn+ds 7* aljicl5n-.0g qgwa/r n-tube pipes spanning the range of human hearing (20 Hz to 20 kHz-+al5/n 7*wn qsmrod c5;nkgl .iaj0g), what would be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz smpib2m--el0 g5h.b uas its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its origpsb.-5m0 h-2mieugb l inal length?   Hz

  An unfingered guitar su)9a mh7y:twkj(g8 litring is 0.73 m long and is tuned to play E above middle C (330 Hz).ywmil:t h8kg 9u)a7j(
(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 Cj hc0/sqg5zri p90nq9 (262 Hz) when the tq09gzs95 0 n ijhr/qcpemperature 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 )kfovgb d/ 9u*v:qu ,r/y 9bsbat 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 hy- rpd4rgzsdk-alp027(o/u jole be that must be uncovered to play D above middlzpr 0ug2lry (j4dps-k7o-/d a e 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 26w eu.6xmlqkr7r -t3:mdhw1f bo.f) k /4 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or a closed pipe.r ft.r 6xbo7)e-k/hlqufwdw :1k.3mm ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long i 1bekxbwyji,5s (i w1syk3 m,)s open at both ends. It resonates at two successive harmonics of frequeny11xe5bm,s,wj (y k iks)bw 3icies 275 Hz and 330 Hz. What is
(a) the fundamental frequency,    Hz
(b) the speed of sound in the gas in the tube?$\approx$    $ \times10^{2 }$ m/s

  A pipe in air at 20 /g;7 5(j tbpbto1rgw molv;4t$^{\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 pr-ie m b62ctg;yesent within the audible range for a 2.14-m-long organ pipecy2;g 6mt-ebi at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is apprh vsyqle0.3sm 6yd)cxq/ d-s/oximately 2.5 cm long. It is 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 canal. What is the relationship of your answer to the information in the ghq/smv / 6) dsy0dlsyqe-.x c3raph 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 m, w)np *h,ipzto adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other si * ,pwn,mh)pztring? ±    Hz

  What is the beat frequency if midtyo mgx72eu4*v(2 rm kdle 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)q;*y mm 0g rx;2udgmo (brand 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 simult2rdm oqgxu;m0 y;mg)* aneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz t-3gpnh /:lu hiuning fork and 9 beats/s whenni /h:lg p3-uh sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hzd+ 76oicbl ,1gxnkydv:ppl 7;. The tension in one string is th6;pgv,i +byc p 1l77knodxd:len decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical *ughk72dsus2s kps* ;flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other* 7uupg;2sdhkks2 ss* at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequenaz 1v,yjy 8j 1-zjz69zl.oduacy 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. az azj6lv jd9y-8u .y jzz11,oWhat are the possible frequencies of A and C? What beat frequencies are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A person stands 3.00 m fr toyd3 .ep5,c*s6cbvy65a p sxom one speaker and 3.50 m from the oth5o,bect.p*y6d3x sy6 v5apcs er.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating at 132 Hz, but a piano tunerp8s3p1 z:kknhy6 l-jk 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 other ? 6pkjz3l1 yk8-khn :ps   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 o mn zv7jpqdvt/t6(0q+f wavelengths 2.64 m and 2.76 m in air. How many beats per second will be heard? (A vjpn0vdmz(t/ q7q+t 6ssume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz when at re29 v6u*w1wi rfppmny 9st. What frequency do you detect if you move with a sp * fp91 pww6yum2irnv9eed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. Wh6r0 unkvvff/i1ks39z mjr3q xxay43 2at frequency do you detect if a fire engine whose siren emits at k33sj6 frrxi am29 vv fkz 0uyxq143n/1550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shiftrh0wc -4 ,tbm5e*eihu in frequency if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they close? 0ewh b-c,r*ue4i m h5t$f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with tqx6ni7hg2lsw5n 8 8je he 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 hear7s ih w8nq l8j5exg6n2s 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 ou 5ipj6ht0scu6qm6ym ;t ultrasonic sound waves at 50.0 kHz and receives them returned from an object moving directly ajm5;iu6ycq 6t 0mh6s pway 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 Au(d1r t6woq)uyobeff0;5ex ,k q+c/cay)p q0 s it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected w5 qy q(tkfo0)uepauw6r/q cc)yo0+ ,e1b;xd fave?    $ \times10^{4}$ Hz

  In one of the original Doppleqzp*6mt3 (3f vyw9n z6.iincir experiments, 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 stationzm t6z3 civ69wy3 pnii.f(q *n. 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 to measure blood-flowq,k 90t vwox0a/c.by q 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 arteries0,caob0.xq yqwkvt /9 at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of freque;f/ mi3jq5v)l ez lz da/ k;*t2x6xfhwncy $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequency 570 Hz. When the wind veloc d8kpq,;l hc9s c:e7czity is 12 m/s from the north, what frequzdlpc 87k9cecs :q,; hency 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 /,bv(mumeovsn1(;v7if lbfjmp/ (5 uland if its speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where the speed of sound is 310 m/s (a) udopbzq c:og/z,9w e0 60z-co What is the angle the shoccz6z owpqd-0uce b/oo 09,zg: k 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 atmolp q:yhk2s(4 j3. nbhssphere of a planet where the speed of sound is only about 35 m/s ys3 lj4:n(qp2kb .hhs
(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/slj ekzys9v92a n 6g(di -c-od6 strikes the ocean. Determine the shock wave angle it prod2 k a(n96dv-6ecgjoi l s9dyz-uces
(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 49fkb:sx5 c; oke i+qx),uzyc$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a plaim5qk8j57 coq6erz (: stl u)zne 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 Fig. 12–34. Deeu5 q mc8l)z:65rkz 7(tsijqo termine
(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 downwarjuzku5 j )2:hud from the bottom of the boat, and then detects echoes. If the maximum depth for which it :uku2juzj5)h is designed to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible g9 tdle0b3ghq)xg1:b range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists ofo:znv+z ss chmmn:2) ; many plastic pipes of various lengths, which are open+s: vmszn ;)mz2h: onc 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 fromwsh)9-1f ggnanf x *u6.5alnk a person makes a sound close to the threshold of human hearing (0 dB). What will be the sound level of 1000 such mosqui6 *l5uh fa9nfnx)ga .1k- wgnstoes?    dB

  What is the resultant sound level when an 82-dB so:hmn62ac s2.wh0 scn5; )efzq5 jx sgound and an 87-dB sound are heard simultanen w 0cq5jhgm2ha6s5 sno2):s; .cfezxously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 dBio,:bl luif+ mqhj70gbi) ;2n . What is the acoustic power output (W) of the spea,gn0bm)i 7uj2o+i q:li hlf;bker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated w7pe.5 wlcrw, at 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power outcr.el w,7pw w5put in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devicsvdky5; v (h;z87cb yies over their ears. Assume that the sound level of7;y vk 58hbvsicyzd (; 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 communicatio5 a/3b hk29ap+5,b wab vqcdjtns 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 to4zsg v-en+dz* f -j2 j-7q;rbuzfgwg5 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 viol 8lboe m2i*on*n yp)a9in is 32 cm long between fixed points with a fundamental frequenc an9yo2)b * ni*m8eploy of 440 Hz and a mass per unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration above a vertical open tu)lfz3cn +wmo wc ;jpjux:,f /7be 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 tunj cl/wz o,fupnwj+: c;x3mf) 7ing 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 st2w+ilq 23gqm zk ;:hh d1jnvy2ring of mass 2.10 g is near a tube that is open at one end and also 75 cm long. How much tension shouq3;dz2jk1 2vnqiwmg l:h 2h+y ld 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 onur:ss*i y j .jw 2i1xjtwh93e;e full loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz range coming from two sourcem*x6 h7aw+xdq0 pnsfo1d:. evs. 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.vfpds 6e1xx:07.+q maw noh*d 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 c2m-o amkr t3fre(+ )eponductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of the movino(- e pmr32atk)f+erm g train?   m/s

  The frequency of a steam train whistld,1q7nbrk f.gyq2h8dzb6z + de as it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant velocitqz7dbfng 8kdbzh1.yq dr,+ 62y)?    m/s

  At a race track, you can estimate the speed of cars dg-0pvj vm7ky0::c gd qz5ds4just by listening to the difference in pitch of the engine noz7kv-g4 0j5d0: gdvpm y: qdcsise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11 Hz. Th vz*l2li ;pga ;d5agk1e shorter one is 2.40 m long. How long is the other? apad25g*k v;gil1 ;lz   m

Two loudspeakers are at opposite ends of a railroad car as itk5 r o8e1kyg opfhs :, 5l-,il.vew2x,vwov2n 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 ofe,r iv2k 8sy,hpgxkeo-5 . v2 o:wlwon lv5,1f 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 rujnr/ y ;-g6h0.32 m/s what beat frequ-n h6rjrug y/;ency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s while the moth sehz7f0 ;k:qla j)x3 ois 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 reflexf0jhkl)z;:a3 s7o eqcts off the moth?    kHz

  A bat emits a series of h qe:vlx13bao btp0)i8igh frequency sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the mobq:3 8x) blt a1oi0pveth 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 from one Alpiiz1eb ) 3ul 6v.s:yxqsne 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 3zi6sl:v .)sbqye ux1? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be compromised by the presence o+qs kona zg+f/(i (p -f7ifrf0f standing waves, whic (sfk7i -/ of(n+ zr+iapqgf0fh 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 room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, slender alucl )zi:e;y l,fminum rod held in thzyi)f:ellc, ; e hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, loud, 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 threshon/69x ; taujteld of hearing for the human ear at a frequency of about9etujtn 6 ;/ax 1000 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 avd2oh-x;s 3kn t Mach 2.0. An observer on the ground hears the sonic boom 1.5 min after the ;-s3x nhdkv2oplane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat i4/y +videa s-rst0 /mxs 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