What is the evidence that sound travels as a waveltksg8 r+iak,i 8w8 c0?

What is the evidence that sound is a form of energy?gqh0y ::*0br opwjf+:uqg1 ol

Children sometimes play with a homemade “telephone” by ato m-cgmv*q3xz9 v+g 4s1x ip9ytaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks intom-y9 zqm+v po 3cvx4*i19g sxg 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 air into water, do you expect the frequency or wa7 bf ok4o8f2hevelength to change?oko72f8 e hbf4

What evidence can you give that the speed of sounzj4 b)jr/0k c8 nbg1vtd in air does not depend significantly on frequencj/ jgt4bbc8 k)n0 1vzry?

The voice of a person wl*zk- g679e yctgf;lmho has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect tajl(ed)y/ oi,u lb4 5she pitch of organ pipes?

Explain how a tube might be used as a fil2bl(5x (2mks 2pnhuchter to reduce the amplitude of sounds in various frequency rangesbucs 2x5 hh2( pk(ln2m. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) zd su2z2b-0z4b v4nrlspaced closer together as you move up the f z-4drz20bzbvl us4n2ingerboard toward the bridge?

A noisy truck approaches yoegjzw:, ll 833xf1m ,q4vnl wcu from behind a 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-frequency noise. Explain. [Hint,glwxne833lmw f1cv jq4lz,:: See Section 11–15 on diffraction.]

Standing waves can be said to c.c, of 0i83lsn4i2xu:fzpevgl.pd 5be due to “interference in space,” whereas beats can be said to be due to “interference in timg5.lc4o,2:vifu.fi ez8xl0dnc p p3 se.” Explain.

In Fig. 12–16, if the frequency vi*na4)h hbo 7of the speakers were lowered, would the points D and C (where destructive and constructive interfa b4hio 7)*vhnerence occur) move farther apart or closer together?

Traditional methods ofzh3c. smabq 0+ protecting the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or redub+.qm sa3zch0 ce 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 sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought of asedt6u emwg* ;1 a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves,;61 ee m*ugtwd (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and obs6exuxi 9nq1 8kerver move in the same direction, with the same velocity?q9u1 nkei6x x8 Explain.

If a wind is blowing, oqkim *n54 ltgx6/ ybpsl-*pd, -s nj)will this alter the frequency of the sound heard by a person 4dlnb pt/**j, opk qs56msg x-)in-ylat rest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A mon0oc4c f* 2jqdxitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear the highest frequency for the cx2fco4 *0qj dsound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening fowc zf.+toe s1slwo:-9r 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 length . t- w1slwocz9+e:ofsof the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his shi3-in1dwgfg16rd 7 xa.v6hy i tfw0a/kp just below the 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 in6a0 w/nhw7didxtykr1a1 g3 gv-.f6 f i seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air a0nq-njmj evd9qf dxs3r+tol 1 /1.jr0t 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 drift m09 r.qu8ztqqing just 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).9q mru08 t.zqq 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 makete436r .i0)lsp9qem tg cq5 izs when striking the water below is heqlpmgei43r) t i 6 sq9t.0ecz5ard 3.5 s later. How high is the cliff?    m

  A person, with his ear p;p-8igy n:cqto the ground, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they ar:py ;-qpi c8nge 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 distancel302 xzx/cjeq by the “5-second rule” for estimating the distance from a lightniezxxj/3l 0 q2cng strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the rg qruq6 c0lr2) s0dq;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 intensity is ugrs/8 .n*wi j$2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound) eueh9 2w,k4lauqh 9q level of 95 dB when fired simultaneously at a certaiu4ee9kuqhwqal2 ,)9h n place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplan rygniyr1w*4. e with four equally noisy jet engine 4iwr .nyrg1*ys is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, wc:b:idmtt )* ukk m,ugvqz0 :7hereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the backgdt uzm, iktmq:::kc* 0gb7u)vround noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a pea6ubs**ym.7 kiir.u 1n2-aeriy eo5o rson speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere cei*oy r5i-y2*unaeo re b. 7uk 1smia6.ntered 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 w 0*kn n2l7qsnan eardrum 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 is5udpnck+ij6;uq/4 lrmb 9 th6 vf:xi6 rated at 250 W, while the more modest amplifier B is rate5 j6nbiuh;6 uqv k9plrdi +t4mcx/ 6f:d 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 rl.jcq9pir) * o5v c -dvmleq;,egistered 130 dB when placed 2.8 m in front of a loudspeaker on the stage. qj,rpm- 5v*9v;iceo)q ld c.l
(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 typic2 h fwb5kqbj4)ally detect a difference in sound level of 2.0 dB. What is the2bf bk4jqw)5h ratio of the amplitudes 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 what fac yjvqy3l2f08stor will the intensity increas qjf3ls0vy8y2 e? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement ampliz:,0k v5 ypvjotudes, but one has twice the frequency of the other. What is the:kp5vz y,o0 vj ratio of their intensities?   

  What would be the sound level (in dB) of a sou9n ckaljoldza:s4 /c05b1+0pqg)g p tnd wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 3q0za c1 5 )ldo sgplc gtbp+4k/j09n:a00 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100- ;21mco2 4jcri8s8 bbp7gig2 7ycee ze3;mmvvHz tone that has a 50-dB sound level? (See Fig. 1 8 r2y bocze;v212e8bgcgec3 m7vi7 4mjpm ;si2–6.)    dB

What are the lowest and highest frequencies that a jtfpb1,s3p(yfc9409o vac-e0lzlqa n ear can detect when the sound level is 30 p,lp y- astfe4fcq91oc( z3a90l0 jvbdB? (See Fig. 12–6.)

  Your auditory system can accommo5vu 2(6hl kdsjj;c5lg date a huge range of sound levels. What is the rgk5hjlj6(c 2v sd;lu5atio 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 frequency of 440 Hz. The lengthbkbq/ ru+ r+-r2/fgog of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tensqrgo-++fbrb / g/kr2uion must the string be placed?    N

  An organ pipe is 112 cm long. What are t.2,u gq(2o hnmps xj;whe fundamental and first three audible overtones if the pipu,n pg( o w2xh;2jmsq.e 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 blowed/p 7af 6.6cjfa1ysh6 qi0 yxing across the top of an empty soda bottle that is 18 cm y66d/ h10. se qyjaiap 6cfxf7deep, 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 uj v *nqz6r1sw.,7zgpthe range of human hearing (20 Hz to 2rv1wqs6 .gp* 7uzn ,jz0 kHz), 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 as its third harmo:ichnln8pkyf- f 4a, 0nic. What will be its fundamental frequency if it is fingered at a ,nyk84fcp-lf0hi: nalength of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tun -,z;pze emhz6ed to play E above middle C (330 p;hze m6zze-,Hz).
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that emits middle C (262 bmyv:4 pn4 lb,Hz) when the tempera4lb:vy mp4 ,bnture 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 n t( yza(dcv+vrni- exu3*:d: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 Exampla/55 0k /atsvkb1p/ knurh8gue 12–10 should the hole be that must be uncovered to play D abov//runas5ua8k/ 5pkkvg 0h t 1be 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 dzc5+ro ch( 2aHz, but not at any other frequencies in betac+c zd 2r(o5hween. (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.7yh1w+pqf5ua jvjw )km d:*2n It resonates at two successive harwf ya 1)k5n+u*qhwd 2jvpmj :7monics of frequencies 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 7 gc)*s w2oz8kg vd-hm$^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are present within the audible range fo9eq mn tk2k*gk xb:x0*r a 2.14-m-long organ pipe at 20 eqktk0g* *92:kx nbmx$^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is 5wi pzx2jjy) 234 ekzf0 bcvu5eb ;we9approximately 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 answ 4pk5);w b e0ex93jyvfzcw25 2b ezuijer 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 tryiye,0g3ze2wqyu 3omz ( ng to adjust two strings, one of which ise,gq3y e uwz z032omy( sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency 5(3uwbsh247ft h lwauif 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 X) operate(*pq5 iw kn-xn -pq.7gbx3 mbns 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 plaw-.i75mn 3gp qkn*(nqpx b-xb yed simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fo 8kai ko8i1 al-y z.fi4sl6l/rrk and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain y-/illo.1 4ify ail6z8s8k arkour reasoning.    Hz

  Two violin strings are qgfac40 bwh49mea jgo.o. ;5xtuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat fre 0xj.5obwam c4gq4hg. ao ;9fequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play mil.) bfzafx4 n+ddle C (262 Hz), 4l)xzna b+.ffbut 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.dmi3t3 c,wl2cx3d9 zz Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possix3ticdlcmz wdz,2933 ble 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 :od8 g tj3qs- cvw9/)fafeqb8one speaker and 3.t3/ o)8wqe 9g-fbc:sdvj 8faq50 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 supposeir a 0iuj5d4*gd 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 vibrardij4u5i* 0g ating 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 2.76 mmhn8b s1l3u4x in air. How many beats per second will be heard? (Assume T = nu h 4s31xm8bl20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fid0w 9.-/cuz typwnnz-sz)w: f b9xf h(( q3jfure engine’s siren is 1550 Hz when at re)z .wwsz(0hf dfy utzq:9x-9 bf njw pu3nc(-/st. What frequency 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 frequency do you detect)qc* r6le;da3vl7lj (alk u)nn i1d 8w if a fire engine whose siren emits at 1550 Hz moves at a speed of 32 m/s 1 )nlanljl*rv(w 7;d86)e 3ulaqc k di
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving toward y/z:0hubhb mt 0ou at 15 m/s versus you moving toward it at 15 m/s Are the two h:0/ub0 bmt hzfrequencies 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 2m i7ys jj,hu:5zzb o/is at rest and the other is moving toward the first 5objhjm7 /szui 2,y:z 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 ultrasonic sound wave5 3 m :dlw739heqmiw 82jhuldes at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the rejmem33 82d:9qiw we huld hl57ceived sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it ga0 0cn3xh) hv/ef2zmflies, the bat emits an ultrasonic sound wave with frequzmvfhhecg/0)2 x30n aency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the originn die k j9xnor//4m8um,cs0 l+al Doppler 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 station. What beat frequency was he+ dx ,m0n/kucis o4n/m rjel89ard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound wavedr ;zzc l-e++bs to measure blood-flow speeds. Suppose the device emits sound at rcz +ez-bl;+d 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 the sound source?   Hz

  The Doppler effect using ultr5bayn+ 4xb0gu asonic 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 frequenci9/desa tmrz ;ox 6;4ey 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear wh 4a/ ;tid6rs9oxzm ee;o are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if pxy-7aem)dr, 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) Whal49 8ecobinfg6 q m)2rt is the angle the shock wave makes with the direction of the airplane’s moe9)omcgl6i 4 f28rb qntion?    $^{\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 tha:e7;pg fkr e hg e:i pmxz:15):/wjrsin atmosphere of a planet where the speed of sound is only about 35 m/75a::xrg1g jpmf w)r k;i: espeh :e/zs
(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/e;h5 jv0 h 5hu 9z 0tq;qn)df kb.boimtj81zd/s strikes the ocean. Determine the shock wave angle it produce1;zd 0t8 jim9)b h5ktjqq0hb f/d5;hvz .oeuns
(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 1+wv yl-vrg9q e gao/.$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly ovegk0lspx+o9 e q. dl0m+rhead and see a plane exactly 1.5 km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal dq9m sxkode0l+ g+0.pl istance 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 uc7 q/a)jc hh)vd0uz6sends 20,000-Hz sound pulses downward from the bottom of the boat, and then det )7 /u)h0hjdazvcc q6uects echoes. If 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 .x k/vaiok-4bjf9+kpoctaves are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists of 7bfw9pq,+ dw8vi)s f 1r/hfw umany plastic pipes of various lengths, whi8ids9 rp /w uhwfw7+vqfb1f,)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 makesek d:zc ,na(7s a sound close to the threshold of human heara s:( n,dc7zkeing (0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an g 9fovg4ao,ov2 kaxh, q7rp*087-dB sound are heard simultaneous4f 7va,p* 2k,g o9 orqgho0xavly?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 dB. What i rvgb nfsf-7.9o fw7 aer0y*)ls the acoustic power output (W) of the speake*0 )ef 9w lfgav77f-. nyosrbrr, assuming it radiates equally in all directions?    W

  A stereo amplifier is rahshk3lyi 1*2tw t; 5xoted at 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the poi;t 1hw2l3t*s5oykh x wer output in watts at 15 kHz?    dB

  Workers around jet aircra uyx 3g1r) k i 9d+ zj38dt7iw-j-zwu7sj(tlekft typically wear 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 radiuswuz- 1) -g9dje8jtzxr3uyw+s (j k7li3t7 dki 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 communications syseca1hs o x( k/lho42,mtems, the gain, $\beta$ in decibels is defined as
$\beta$ = 10log($\frac{P_{out}}{P_{in}}$)
where $P_{in}$ is the power input to the system and $P_{out}$ is the power output. A particular stereo amplifier puts out 100 W of power for an input of 1 mW. What is its gain in dB?   dB

  Each string on a violin is tuned to a fw 3 uv gq13ri xf0sh-dis;;j+lrequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long be 9sb +jj5canb)-ysy y.tween fixed points with a fundamental frequency of 440 Hz a+yb9njybsy-). j cs5and 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 vibrati2+m a0mu), feimd qh1opo;d:h on 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 p0a)moum:e+;1h dqm2io f hd,level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of mass 2.10 g is near a tube td 2r5jfmkjrd, . qy7qm*v:m/ihat is open at one end andkq/*7jmdvi mj5 2:.rm ,fdyrq 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?    $ \times10^{ 2}$ N

A highway overpass was obs*l 8po 05uv :vlz w;fv.lil/byerved to resonate as one full loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in thk7bg0n 1rwe. he 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 r1bg0.w ehn7ka point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-,vxg+,2 eqp + p4y8kzuhhdbr.Hz whistles. One train is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the sbpz24pduk,r8y+.gveh+ h xq,peed of the moving train?   m/s

  The frequency of a steam train whistle as it approaches youm9d8qctvsn*, *n(lys is 538 Hz. After it passes you, its frequency is measured as 4 ,tq*sdcy(vs*8 nnlm 986 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars just by listening to the/e5-:l-uzsi vc icw+ m difference i wul 5+e/-cmiv-: czsin pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11 Hz. The r mmmjl1: t4 v88pli,pshorter one is 2.40 m long. Ho84 lvr8 p 1pl,mmtjim:w long is the other?    m

Two loudspeakers ares),a je3,ag:eob ztqum4ph 91 at opposite ends of a railroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of ,1,oea3 e qz4hasm9 j: )pubgt212 Hz, what is the beat frequency heard by the observer when (a) he listens from the position A, in front of the car, (b) he is between the 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 vt9ijq8u) 0f nwhat beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flq90j iuvtnf8) ow 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 t,;9+qopmcs xbsb7 5yyoward 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 waxcspsy+ q9y 7b5,; obmve reflects off the moth?    kHz

  A bat emits a series of high frequw1ff;xu r5 fwd-nqhy0 ,t,rj,ency sound pulses as it approaches a moth. The pulses are approximately 70.0 w, f,-5frjqy1;u,hxt0drfwn ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once 0ixh (em(px*hused 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 musiep xh(imh*x(0cal 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 tube.

  Room acoustics for stereo listening can be compromised by the presence dkolk, 9 fflz ;)ns*ij2qe9 4hof standing waves, which can cause acoustic “dead )9;fk*, lq4nlf sk2ejz io h9dspots” 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 alumint5m 8ul):fcvxfhg5kz (, 8zv y/)vjpnum 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 t88zvffvh cug ()5n5:)x/ lkpmtyvzj,o “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 h. dd hc)21,zwuju+gj wearing for the human ear at a frequency of about 1000 Hz i+hwgj uw1czd.j2, du )s $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on the ground hears the sonic boom+x:g;7ya m9qqfk9wp2 nm maw+(owop8 1.5 min after the plane passes directly overhead. What m2o(p ;awmwg+ w9fqaqoy8xn + 7k:mp9 is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboaqs4.5 r -gdqllt is 15 $^{\circ} $ in a lake where the speed of the water wave is 2.2 km/h What is the speed of the boat?    km/h