What is the evidence)zis oo oavd;ru6 78t :jy8sn6 that sound travels as a wave?

What is the evidence tuab /0xupj4p5. j*yx -jaue m,hat sound is a form of energy?

Children sometimes play with a homemade “telephone” m*8lw:i h ,6 /e3vfyxbh.sui2p hyu0q by attaching a string to theh /6.quf8uy023swmb :ii lv hh*xepy , 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 cup to the other.

When a sound wave passes from aijh 5mw kek1mer1 2k440 , 8kxgxqpah;ir into water, do you expect the frequency or wavelengt w,k 4kij2 h01m8keex5mp ;xg aqh41krh to change?

What evidence can you give that the speed of sound, lx+y/rtpmqo(b d.q0 in air does not depend significantly on freqq b/pry d+oq(.xm 0,tluency?

The voice of a person who has im k2n ;r2ukq xp7d(kp;nhaled helium sounds very high-pitched. Why?

How will the air temperature in a rh p mq;dfszj.2 ;cb ,p7iyk7r(st36u yoom affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce t.)y 2 *fmkj p*olmf,zlhe amplitude of sounds in various frljpf.2*,)f*k zoym lm equency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spacee;/c6j szxi .gd closer together as you move up x6;gze s j/.icthe fingerboard toward the bridge?

A noisy truck approat3x wu-z5 .*(edr lhqwches you from behind a building. Initially you hear it but cannot sr.5ldx*(wezut qwh3 -ee it. When it emerges and 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 b,qi76 6lomstzciv 5a 7e said to be due to “interference in space,” whereas beats can be said to be due to “interference 7l6,sc it5v zo67iamq in time.” Explain.

In Fig. 12–16, if the frequency o3gaof (ty5y1/ 1 zq7r6mno; l 0cxywodf the speakers were lowered, would the points D and C (where destructive and constructive interference occur) move farther apart7 w(qr0dnl1zm ooy15ty;xf /aco g3y6 or closer together?

Traditional methods of protecting the hearing of peo:egqagezrxe(u q 6:l2ql1 k1+2q5fmkple 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 reduce the sof z +2 qr(q uekgxle11qmagk65:q:2elund levels reaching the ears?

Consider the two waves shown in Fig. 1snxcod:sg7, p da)n:2 2–31. 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), arc,s2 :sxdap 7:no)gn de the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source rh1f x:8,lgvmand observer move in the same direction, witm,fhrg8vxl:1 h the same velocity? Explain.

If a wind is blowing, will this 29uj.l qz7rlnmc yau2*jf g+7 alter the frequency of the sound heard by a personqlg u *zju.fa2rml cj9+27yn7 at rest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of arv wgoz2b6 9;rlz2k+hw+h z ,l child in motion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which positiokwzwv ,l 9+2h6o rzrhbg;2 zl+n, 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 listk4xsje;/hi 5hening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the k/hhi5x4; ejslength of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the ww4 j, 0vp:lkaeaterline. He hears the echo of the sound reflected from 4,l:a0 kepvw jthe 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 waq: i,n;wucqz7q33x n: eggm7vvelengths 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 jusotj ( 2 y)bkt*9b(u(y-h uelzst above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much timetz9buy( u ly -shto(b* ejk)(2 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 when striking th.krrx *gd/nfo-q lu; 1oi c;5je water below is heardnk/1d5oc.xr;rjlo u g-fiq; * 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge s 6sjyr.8 e lawj0(u dm)dxzhzt 7lb1 4gu8tz21tone 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,l86u . hzzxdl7 1j u2mtwazb8drs)t(j4ge1 0y 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 mau( + /a/diayrqde over one mile of distance by the “5-second rule” ford+r/ qyaaiu (/ estimating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain levelpaqmd-e :/rp8i14efx dmuu3 s.4tc p2 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 lejo8k2s in ;8(hl; tp+lc:gjngvel of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce mf1n4hq gut z3q k09m b3oivzd1b4;.ca sound level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is explomn c4t; mu1hbo1gqzd4iq bkvfz0339 .ded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally d 7 ;2tepj+adq8fju*k noisy jet engines is experiepu*2 j+ja fdktqd e;78ncing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said td/mtpzsx92ei u ,vknw 728k- no have a signal-to-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 backgd,2u8ne wikn/ tz-mxskp2v 79round noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in normal convgcdd18ay80;r3 x jn0jvlr gr,ersation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the md8;c3 l 0 n01ardj,xggv8rryj outh. $\approx$    $ \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)t uk4y2d7lw kqz(t1 l 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, whil;wvpt oj 9t)jza.wnh q*);fc9e the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point .nj ;fpwtt9* 9 )hjq;a)wvzo c3.5 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 04c k2zy w a9idusy5o7educ9pkmu 6,:2.8 m in front of a loudspeaker on the stage.2d:z9 7 y k 95eyi04mpk6cc,ou uusawd
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound level of 2.0 dB. What-qr+x*(v bbszkxv0 hnju3k +5 is the ratio of the amplitudes of tw( 5xj-kv0vbxk3qzs+ u* rn+bho sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tri vx:p4fr:cv 5b0n*s nhpled, (a) by what factor will the intensity increase? Increxn:vcbsn0* 45hf vrp:ase 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 twice the frequemfj97d(* k,rl xmz;*a rkiuu ;ncy of the other. What is the rati(a*j9i7;*uf,ku md mklrz ;xro of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that c2va2c5i8::5 ef40albg z dizj 6ovtdxorresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz? x clv5z g:bd24j :2atvd5oaef0i8z i6   dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tone t -fcwbcon+u w(k/57avhat has a 50-dB sound level? (See Fig. 12–6.) 5can w-kwb cov(7/+fu    dB

What are the lowest 1isk**yml//xs4ui3m +hf gvb and highest frequencies that an ear can detect when the sound level l *fhssx*b41//k3vmiigy +mu is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a hu z2v 3e3+vdo)f- -pzlx wnz4plge range of sound levels. What is the ratio of highes42p-nzv)oze 3wllvd 3zx+ fp- t 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 frequency of 440 Hz. Theky. 4ebn:x x39ty/)s+a m0do y0 in9ytd8lhyd length of the vibrating portion is3/h0t9my.4 yd0b+ i)ly9dtko naxey yn8 d:x s 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 fw fvecyszr7c,i+ 6 (j/ g9g2dqdip*x 6undamental and first three audible overfpcd2igx+ qd/66g (wj7c y,9r z*s evitones 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 expeca*gre en-z r7a n8palv;,m o5;t from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a cpog7m ;la8n n5z,a ;err-*eavlosed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe ox/p(*oemp 1e ergan with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would bx 1 emop/e*(pee 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 54 ;jy: fi6v3bz lmfq/pnth3+ 6m0 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its originf qlbj+v :6fz;yp6mh3/3 mi tnal length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to plays,y o66f98chf1(cwok1zt bh rc2upw8 E above middle C (331(6o,c8oru2 6 8 w9pbtkzy1fcs cfhwh0 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 ope yq 3f5wvl)p+4 1sv ry*h+wj/xdwxr-pn organ pipe that emits middle C (262 Hz) when the td/fvvp +r-rxx)hs q4w5p +y3 y1l*w jwemperature 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 rb7 cjx nj4qwfr8z h;wj8/5:j at 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 12–9okyed/2h3c,d((aomdj5 t k y10 should the hole be that musy o o (cdedy923md/(htkj ,5kat be uncovered 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, 44b-p4jf jvm01bk 1x5rqqt+5kau; xh2 i0 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or a closed pip5bv01x5 f1juq i qbkrk+th4-;xj2 pa me. ----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 resonates at kf-8ryiq*z)+k0 )tz;vtle drtwo successive harmonics of frequencies 275 Hz and 330 Hz. What l)t;qdrr0z -i*z8ke+yvkt f ) 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 8bolrv fb9 l,*$^{\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 audyh .kkyhev kx; )vsu/30l2g 5iible range for a 2.14-m-long organ lih2s vyk).5 k03u/ vyxghk;epipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal v 9ufjkc1y1+/1f s59k ho f wngu-u1ocis approximately 2.5 cm long. It is open to the outside and is closedu5 uwof11k-o f1fc y+ckhj1u/v g99sn 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 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/9br(czk ewutnv *;7n to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other snzw(cv /7; e9*tbrk untring? ±    Hz

  What is the beat frequency if mid to568e3wrq -ikf h(zcdle 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, whi psb:f;e* q*l7v9esn8v/oc2ne tg ka3p le+p7 le another (brand X) operates at an unknown frequency. If neither whistle can be;/372fnp8*eaenevo s: pslte glcp9 7bq+*kv 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 350cfa)gzue o(e5qesv p5- p3w,)-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the fe)s uocp5, 3eg5qzv(w-a)ep string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hfihu(x6ex8/s++ x (3 + uc/cwcjzwc4ww 4x yqez. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Rec(cqjwu+cxc/ 4i3hx/zxe w+y4c x(f8e uwws 6+all Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play midd 2favlzf4r0m4le C (262 Hz), bl f vm42az40rfut one is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Hz; whey/ +/(k0kb9u qoze uvzn 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 frequencies of A and C? What beat frequencies are pos y9eku(/oqz +bzv0u/ ksible 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 speake z1va+fk t+0hkr and 3.50 m frk 1azkf +t0+vhom the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating a emm,m;0f yktygi 1j;hu02wc64o.qmkt 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the foummti1g0;.hm0qkf6ek;4j, wy2c ym requency 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 2.6 v o+m0sn8e+*u/z f kmfvs8w4x4 m and 2.76 m in air. How many beats per second will b4x v f w8zms*fem8/+ovsn+u k0e heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of w3x ;(j )zafmtxeu.eg0j q)x+a certain fire engine’s siren is 1550 Hz when at rest. What frequeewxjmg3)+ zf( )eaj.x 0;xu qtncy do 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 e)a: b ipw8 q:e4mst/yfrequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of 3w)ap/y:t e 8 s4:qbeim2 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency ivua)+o5(g mjf,.j.tedspxk /f a 2000-Hz source is moving toward you at 15 m/s versus you moving toward u) xej5vogfj+ ./m , .dska(ptit 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 with the same single frequency horn. When one is antwg;w )sd-( st rest and the other is moving toward the gw-s(n ;twsd )first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasoniczne2 gh z2r:;ct5 w*a;rj,l s* jf-uhf sound waves at 50.0 kHz and receives them returned from an object moving dirwfh-rfl,25a uzzcg hn:j2 ;j;re **s tectly 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 flx f,s ozs, x-s-srn,6pies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. W6r-spxss,,x on- ,zsfhat frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was pla p2rqo.ff 2p a8rpqo00yed on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played thr0proqp 2ff0 pq2a8.o e same tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure bloodhva++y 7l3z ocn-j x7s-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 direa7z-osn jx73 vc +ly+hctly away from the sound source?   Hz

  The Doppler effect usinikzo-go; n8 h,h.*vv eg ultrasonic waves of frequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequency 570 Hz. When the wind velocity isms k 2mpc/od.* 12 m/s from the north2pm/ocm* sdk. , 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 movijf5f ssd87(8r0zbbzr-y1y:a lmvgl* ng on land 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 soa r.qszz2rgj79t// mound is 310 m/s (a) What is the angle the shock wm2a 9zzg q7r o/t.rjs/ave 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 ol9,dd+8 hq 8vxsn:sj af sound is only abo8+laq9jd8x s, hnv d:sut 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. Detqej9w2zmm as33k7 gb-ermine the shock wave angle it prob ks-9m3 2qagw7zme3jduces
(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 r4icwrg1y5* wx5o( jc$/theta$ 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 aboz -kreku:idw7x+( 6olve the ground flying faster than the speed of sound. By the time yoro(k: u6lkiw-xe7z d +u 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 froe(,un bbj ft ;o.jy.s5m the bottom of the boat, and then detects echoes. If5ynbj.;sf.j b ,(o ute the maximum depth for which it is designed to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audi :4oz o j yo1kfev(xk+(q+dnk6ble range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists of mg7k4(a* q,dtn fldl5vany plastic pipes of various lengths, whiatq5 l, k4dvdn7lf (g*ch 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 clo2,8;gaf9ezy-e *crac x.fnjise to the threshold of human hearing (0 dB). What will b*yff c.c8ga;ir,nz e2x e9aj-e the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 8(ri5nkkd*5 xisf.pp6 (8i de xa jdm-:2-dB sound and an 87-dB sound are heard simultaneo: x58 dkm jpi-5(xne.r*pidsd( 6fikausly?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 dB. What-1ocve(nak h60 dg9 yw is the acousticgwo6n -c 0adh1eyv(9k power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. Tcpx4h d2q1 g;ov;orj 2he power output drops by 10 dB at 15 kHz. What is j 1coh;dr gq vx;2o24pthe power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective dev/oe*n1l bb* v8;grr/ 0,qxrrgy 5idygices 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 interceptxg/y8g rl q* /0birvo51yrdr e;bng,* ed by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications syste+o3(bxl pwn 8t-jx6fvms, 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 vio1(3g :pasdlriujuo,6 lin 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 32lv( i:2qo i,hu cm long between fixed points with a fundamental frequency of 440 Hz and a mass per unit lengthu(qhiov, li2 : 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 setfh)z cgvpku gr9ce*xzg)z 6n1v y v1l5q4f50. into vibration 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 hevv u 5l61e4*fk.gyxrzvqg9zc)zh15)ngc p0fard 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 that is ohvkh8 45qtwatia33u7 pen 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 tube?a7t3hhkt3wvia5u q48    $ \times10^{ 2}$ N

A highway overpass was observed to remrt0hxb2ulr bi/ 1nf4sgk: 3/m -7 larsonate 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 the8-ae xq3b9zhfpcp qbf54+ m5o 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+4bco q-zbf me9fqx38ppha 55 minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The conductork5uhq(:i km: 6vxh s7fqjfe+ . on the stationary train hears a 3.0-Hz beat frequency when the6f jv7qqf(si:h h 5ue:+.kkmx other train approaches. What is the speed of the moving train?   m/s

  The frequency of a sl.pfs20 lc3tk team train whistle as it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving (3clf2.sl0 ptk assume constant velocity)?    m/s

  At a race track, you can estimate the speed of c2ifdal6wc3j g0odnw z+8 1i5cars just by listening to the difference in pitch of the engine noise between approacwcwil jco 1d8d5 0n6ia3z+g2fhing 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 beah 6f.+qr 4wt czawnv,8t frequency of 11 Hz. The qtn+h4,r z f6aw8c vw.shorter one is 2.40 m long. How long is the other?    m

Two loudspeakers are at opposite end *ixbmr 39v(f++c5nscsbr :hhs 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 freqhc xb:95+cmsrv if *nhs b(+r3uency heard by the observer when (a) he listens from the position A, in front of the car, (b) he is between the speakers, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of bl8wle5c ,d yeewv7r07l6 /ew ofood flow in the aorta is normally about 0.32 m/s what beat fr,o 7lry85/d e ee vfl67wwwce0equency 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 spek(4m dixdu57w .v:gfn .pv 4jnuq0q:led 6.5 m/s while the moth is flying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHdqlkn::ujivn7pwg. dvxqu m54f 4(.0z. 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 high8cjzcz as(9((ka0 zv+ ug zbl4 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 moth be detected by the bat so that the echo from one chirp returns before zv zg aza4 cl+(z98su(kj(cb0 the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signalskbxb azju-h)6r8v0f( 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 tu -k( 6frzuahbjb8)vx0be.

  Room acoustics for stereo listening can be compromised by the presence of stan : aiq)q,e1ik49bksawf)hgw8xc3kk6 ding 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 fundamentala1fcskwik)akk 4 x36eih8w)q9,q:b g frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “. tx) w;s ;a-h:m* xbtu-kborzsinging 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 be made to “sing,” or ex-t;ts .rx b;w:m z- ok)b*haumit a clear, loud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the threshold of hearing for the human eat;/1p7z+ wbir p n0nifr at a frequency of about 1000 Hz is;np7in+tp z1r/bf0 wi $I_0$ = $1 \times10^{12 } W / m^2$ 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 observe r907l;l8 puxcomjn23 hoem(dr on the ground hears the sonic boom 1.5 min after the plloo3mxp jhu;m280n(7 ce9r ldane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 15(vhc: zw sa i 345k1lvzrabv(rs)2p78xy jj2x $^{\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