What is the evidence that sos6.q1fa(m i4x3.wnp dth1wzg und travels as a wave?

What is the evidence kp h xyvp6q79r5he(m a+rdw71that sound is a form of energy?

Children sometimes playj p64-uq:w4t6vhsibr with a homemade “telephone” by attaching a string to the bottoms of two paper cups. Wi-:tprvu46 wsj 46h qbhen 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 air into water, do you expect the fresdun0o xd-d 10fn 2e2wquency or wavelength to cha2 1 -ds0wodf2 xend0unnge?

What evidence can you give that the speed of sound in air does not depen. n+y*vp u)dlgd significantly on fren.+p gv*d)l yuquency?

The voice of a person who has inhaled helium sounds very higrcik.,47q x5*-uxs1hi i/ a 9b lwlzvjmzts83h-pitched. Why?

How will the air temperature in a room affect the pitch of i ca l+(bb4s9nr zo u+)5-1g6 byfxaqgorgan pipes?

Explain how a tube might be used as e ou, ed/5*wohq)up)d.p h)bga filter to reduce the amplitude of sounds in various frequency ranges. (An example is a car qd,b5/) u p*uohh.pg )oewe)dmuffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as y3v 8 w0+-4ybpzjtjx5j pe 7qe ;wx8jom:xjsj9ou move up the fingerboard toward the b3etxw j-7j:jewsbx j8v jp ; +4op5 zm0xq8jy9ridge?

A noisy truck approaches you from behind a building. Initialx2 q9ujw))ru+ vnrh x,ly you hear it but cannot see it. When it emerges and xu2+j u)hwrxv,9q )nryou do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said8 3+oi(yin;u r4zugo60dw jcl to be due to “interference in space,” whereas beats can be said to be due to “interference in time.” Ew 84;+3 rl(ndjuy6zcigo0oiuxplain.

In Fig. 12–16, if the frequency of the speakers we;- y.tw4c bexxre lowered, would the points D and C (where destructive and constructive interference occur) move fartht.eb x-y4 c;wxer apart or closer together?

Traditional methods of protecting the hearing of people who work inb.am.z z/r ( tcs94ppf 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 sound lrzs4zf .pacmb(/.p9t evels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each zblx .+:*vgh qwave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In whic.lvbzq*gx :+ hh of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if czx9rw9q,/*wpl b8d tthe source and observer move in the same direction, with the same velocity? t9c8zwxrl/,w* 9dpbq Explain.

If a wind is blowing, will this alter thnr7f)1hkba+9 e mjw yzm:qy04e frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or vel:ye0zrm+ jy79k4q)1 fmnhb a wocity changed?

Figure 12–32 shows various positions of a chil)a rmn()muuw u0ir/5hd in motion on a swing. A monitor 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 sound of the whistle? Explain your reasonrmi a u ru))5wu/hm0(ning.

  A hiker determines the length of a lai1mr65 p.po nkh t6z-8q+ad+4wdtvqkke by listening for the echo of her shout reflected by a cliff at the far en64rzq6-pntovathd+ 1kiw+. 8kmpd 5qd of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterlinzq8u2o +(c5sjtt:us te. 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 1560s+oct ju 28sz(tt: qu5 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air at hdcmq-( tp1 mk-by6 y520 $^{\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 schoq0 6/(o3/7avy ew dt eunpo:izol of tuna on a foggy day. Without warning, an engine backfire occursu3 7wq zd6(y/aovpt0e: oin/ e on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes 4wi)-rwwnfi / (ch9(hib4iu;kf sc , pwhen striking the waterhpi(-kis 4nu/;iiwh f)9wr4fc (b wc, below is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the grz (ti fqcbr 3u8)ep.h1ound, 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 are 11u8f(h3qb rp ct.i)ez.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 oq7ty44u22b xe1u nxl(hwq2 bqf distance by the “5-second rule” for estimating the distance f42qqw qb2xu 2n u(7 1lebxhty4rom 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 leve /5th0v9odqk gy,ih2+8 xwegll 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(/0he ylkz vskknvub ;+/bp 4( a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers producg-:*rg tz hejmzv-5k)e a sound level of 95 dB when fired simultaneously at a certain pz h:t5--gmvzge*jk ) rlace, 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 anm ueangibrlz0gq 6 nvc;4w7v9;y4d *8 airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captac7;0nvim*aw r;qnzu4 d8egy9 gb46vlin shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is/bvazvowa0 o( x:5e ;w said to have a signal-to-noise ratio of 58 dB, whereas for a; (e0o5wawv/:bxo v za CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of uopkmh x3of5q.91:6 j:tembzf 22/+tjg wu ensound from a person speaking in normal conversation. Use Table 12–2. Assume the sound s.jt pm19 ugkto2:wfuq :xe6 /+hn2 bzo3jem5 fpreads roughly uniformly over a sphere centered on the mouth. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave strikes any r5wf it*qw-6r*d yl6 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 is rated at 250 W, while the more modest ampli ox/1 7.8jhlh ginp)wlfier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a nj8/xgh)l7i 1lhp.wo 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 f1it 8bwopm* zqief,3u)p., pdB when placed 2.8 m in front of a lo bpqmf1,t if8p *iep3o,)wz.u udspeaker 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 tx hb hr7yb1(257k ;sibxu :fgdetect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Sectioni1x t2;( kghf5:uy7b7rs bhxb 11–9.]$\approx$   

  If the amplitude of a sound wave is n3 5 kn.hysor; zc7mw1tripled, (a) by what factor will the intensityo nr1h3 wksmnc7.5;yz increase? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has 3b /izwy6;58sqey uma6l0 )wat yyub3twice the frequency of the otherb;/mqz3 6w yia) l0bayweuy3y56tu8 s. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that corresponds ;jntz c5eayq*xi k65 k,::tatto a displacement amplitude of vibratingn t5ic: k:q;a tazt5kx,ye*6j air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what so s o. n oau+pc 5tnfkns;0slrn50*z8l*qa-5yzund level to seem as loud as a 100-Hz tone that has a 50-dy5sun5n f al-+ **s0nl.a o85q 0nk cpos;rzztB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect wh if+w j lwwpmf0;6,is4en the sound level is 30 dB?mjl 406s wfiifp;w,w+ (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is the y gb+)lvjo+obxu*z q453r9jlratio)9ryluqjj4glz5 bo b+o+ *x3v 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 h3pv-:q3ln bltus 2 rnf6m-q dv-9ceqsz( 76 rfrequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 9 -d usmq2s3v rvzbt3qq:6n7f pl-he n(6l-rc g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental) js-slzs 2mq-3xl8 ulk8 i4br and first three audible overtones if the pipe i-4xs) - 82bslik 3zum8srljqls
(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 expect6z4 9 fhi2tzg+9vu:crc9b gnu from blowing across the top of an empty soda bottle that ig4t:vubz9r gnif u +c9hc6 z92s 18 cm deep, if you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pipes spag +rhpmmqr h ,v y6tc:(.qv9;+ dg1gxqnning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes requig(p,+r yqx+vmm1;t:dc9g g qhq .vh6rred? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmonic. What willj 2on(fx rkba i6usf4w:vj;). be its fundamental frequency if it is fingered at a length of only 60% ons ofjr)k:av4jux ;f6(i w2. bf its original length?   Hz

  An unfingered guitar string is 0.73 m long and iuu3s, aq2ip s mw: 55dgp8fm0ws tuned to play E above middle C wuuips5gs,fd w 3:2m qp8ma50(330 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 ans 3kn7rdc o-ukzwii- qpz*6p30/rq9b open organ pipe that emits middle C (262 Hz) when the temperatud-ckr*i wzskq9oi /7u3pq6 zb3r np-0re 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 ayvtr9v9ewr9v7 kn3xwa c 4o-cn r53b4 t 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Example 12rat5k5so vzfc0 ) *g1k–10 should the hole be that must be uncovered to play D above middle C at zgatkvosk5 5 1 0*fc)r294 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 cfa6 )1c gm 2k9by,hkmat 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why tymb) 6hk1,g9ca m2fk chis is an open or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at both ends. It resonates at two sawbwf a1*/, /ut. znrsuccessive hanz.f /sw tar/ bu1*,awrmonics 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 e hzu rh*;-;abtd3g(h$^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are present within the audible range for a 2.14-m-long ymsdw,*teuyq 4rc *,5 /gpax9 organ pipgs,y dq xy /5awc* m,rt9e4p*ue at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open to mtcju 4 8u)q2kthe 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 yourmj)cu8u24qtk 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 2 qevq4xcs3q, every 2.0 s when trying to adjust two strings, one of which is sounding xq eq2sq, c34v440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz)73txc o i8ww7mr+t+ lkj* m8tks9u2ji 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 x r0 yyi::s0hr) + 3fpst-btacanother (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played sep30y aips +fr::t)s c-0 xbythrarately, 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 350wi +-rd 4fgt*z tp yza1l-w*b,-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning for argpb+yw -dl4,1zz*f*tti- wk. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to they )r5r6ii n,l.n+n q vvm6btz9 same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat freqvn6 +rq6 mb.lvtr)znnii 5,y9uency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two ide1 176zcfc kwgpsb0x1s ntical flutes each try to play middle C (262 Hz), but one is at 1sk1 z cps0w7c6fxg1b 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and ihfmqz l9tj8z ;6r+/a C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are sounded togethe+i/9 j qtlzah6f;8 zrmr?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1 mpue91rq52cbu 8 nj0o8g 7rob.80 m apart. A person stands 3.00 m from one speaker and 3.50 m from the 2n17u 5 g cruq 98epoomj8bbr0other.
(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.0b bjo lkb/8jt 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played too /kj8lbj.0 bbgether. (a) If one is vibrating at 132 Hz, what must be the frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound of wavelengthi*mtx.swo i;12d-r khs 2.64 m and 2.76 m in air. How many beats per second will be heard? .imtxw rs * dh21o;ki-(Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certainl 8g w;uo1cgs9 kg)bx+-qbax8 fire engine’s siren is 1550 Hz when at rest. What frequency do cak)g xs;1o8 8+- gbugw 9blqxyou 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 if a fire e 8 vwiaqwsfo dig21s9p y7s(fwm:-65ongine whose siren wf:1s 5s(va2 yif8i o gwod69qsmw- 7pemits at 1550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving toward vs e 4r5uhvk/ao33w:h you at 15 m/s versus you moving towaskv:rh a/we 4v3hu 35ord it at 15 m/s Are the two frequencies exactly the same? Are they close? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with the0:s n: ;xwfrli same single frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? ni:lrx 0:;fsw Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at krz- tnu 3+4hr50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the received sound fr+ urkrh4 tn3-zequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, zw3:n gob n2g25vpoh7the bat emits an ultrasonic sound wave with 2 po v37:hgbg2ozwnn5 frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a hske(1vko x)(rj ++xlmoving 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 heard if the train car approached the station at a speed oolxrj1(k+s )+ hvxek(f 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-/se5 i)lbusf7o2utovjy/ p 59flow speeds. Suppose the fu7i5ovo5st2jb/ s /l pu9)ey device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of frequuucm(/ifs 4f)zb k q*axz*2c;ency $2.25 \times10^{ 6}$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+j4hhdb,ir4+ x z ph2ze38uve sound of frequency 570 Hz. When the wind velocity is 12 m/s from the north,2ze,b84ui xjv 4+p+h hhzre3d 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 movinbyx5cs +3 4z vxt:tu+zpe8 k2lg 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 t+nu 4lckpre.2 rb4x,where the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the directeu4bt4. rkl+cr ,nx2p ion of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmosphere of a planet where the speed of sound 0qjplk dd).kqh0r 9 3bis onllq9kkpd)0r qhb j d30.y about 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite travelineclh.npv( o5e +la4o4g 8500 m/s strikes the ocean. Determine the shock wave angle .p+l ecoh54( lan veo4it produces
(a) in the air just before entering the ocean, $\approx$    (Round to the nearest integer)
(b) in the water just after entering.    $^{\circ} $
Assume T = 20 $^{\circ} $C

Show that the angle lpol5cp8 ;pp 9$/theta$ 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 exactlywar-xcz (/*w1y.9b rxr el+ak 1.5 km above the ground flying faster than the speed of sound. By the time you hear the so y wr1klx arr+(-wbx 9/c.eaz*nic 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,wd. 9de zz(.ds000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. I dw 9dzz(..dsef 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 +ms.g a1w k5yhin the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. xdvb +wsqg) 6 w,8isk5o33adhIt consists of many plastic pipes of various lengths, whichqah6x ssb+k vi,g35dwd) 8o3 w are open on both ends.
(a) If the pipes have lengths of 3.0 m, 2.5 m, 2.0 m, 1.5 m and 1.0 m, what frequencies will be heard by a visitor’s ear placed near the ends of the pipes?
$f_{3.0}$ =    Hz
$f_{2.5}$ =    Hz
$f_{2.0}$ =    Hz
$f_{1.5}$ $\approx$    Hz (Round to the nearest integer)
$f_{1.0}$ $\approx$    Hz (Round to the nearest integer)
(b) Why does this display work better on a noisy day than on a quiet day?

  A single mosquito 5.0 m from a person makes a sound close to the thre;b 3iw fpuk6a+shold of human hearingb6pw3f+ iu; ka (0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sxz dc7:p:l.g pound level when an 82-dB sound and an 87-dB sound are heard simultane7 gz: p.pcxd:lously?    dB

  The sound level 12.0 m from a loudsyh v(m):nfk.h peaker, placed in the open, is 105 dB. What is the acoh:)f nh.v m(kyustic 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. The power omnw. rnbu .j1skl-gq, t ::-goutput drops by 10 t-ql:..snw1 -k,g:gmbo rj nudB at 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft f m()+ l9aatdwtypically 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 radius of 2.0 cm(mt9+)fal ad w. 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 e 0mg slu)8eq cz0l(7 cm)txo: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 to a frequency ky8j g lg281(en0nxx p1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long between fixed poiojo,p654gke ./-0pibklw a(x o.d hgdnts with a fundamental frequency of 4 od.hxa ,wgkp(li.j0do / pe o6b54g-k40 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 tubes,+cy m *;wpr8n vvuv-x r./gg filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distar8vcyg v,nwu -mv *r.+xp/sg;nce 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 0, vzpxade*efo;hzdo1:/ ;wq a tube that is open at one end and also 75 cm long. How much tension should be in the string if it is fw eq,o0o;d/zz hxa*e1dvp :;to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observeehtn(*h;ry -k bs ecy59 77qevd 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 the 500–1000-Hz range coming 5rbttj-v6kl +from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, th+-t kb6tr5 vjle person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationah6xa;x qt (pv(4/po agry. The conductor on the stationary train haqxavpx6/; t (oh4g (pears a 3.0-Hz beat frequency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approachlm2(boetohto .j04.s es you is 538 Hz. After it passes you, s2m o0 b4o.(eotth.jlits frequency is measured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars just by listenqnz(syw 8 :qz)j* i:dhing to the difference in pitch of the engine noise between approaching and receding cars. S:yin h)q:s( djz *8wqzuppose 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, produ6pges p 002dt s/zalid7 ; ,(b3pytbtqce a beat frequency of 11 Hz. The shorter one is 2.40 m long. How long is the other?e; i06tdyb 3bp2g tsd,7z (qpt/a p0ls    m

Two loudspeakers are at opposite ends of a railroao ff(u2fgoh/ a)2d8owdn 66bjd car as it moves past a stationary obj/daf)(o wd u6b68f hn2ofo2gserver 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 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 mn 7fyi 8qg 3*lc;p c8hdc(7cdis normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves we3cdphgcl87 q cmy8;7 ci*fd n(re 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 spjj,qmv 60 kn)deed 6.5 m/s while the moth is flying toward the bat at speed 5 m/s The bat emits a s,6q vj0d mk)njound wave of 51.35 kHz. What is the frequency of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high 5ycl.cpby:;e 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 the5bc y;:celpy. echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–3tsq+cch2n3ovy7 c,k o(o. - zplt6 4hw8) was once used to send signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to creay4swkt n 36ohlqhoc2,o.(p+zc t-c 7vte 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 tube.

  Room acoustics for st:ugd, pcp.ib9j 3 rtt8ereo listening can be compromised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamental frequencies for the standing waves t c:pur3t.9gbj8i,pdin this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, slender alum 2gbtub:8l/z1j/zbmc inum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand1mz /: b 2cug/8bzbtlj. 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 threshold of hearing for the hugr hi t;u9z2fk2wbcttc0,m7 9man ear at a frequency of about 1000 Hz 0fgb kic7 92tt9; cz,m2 huwrtis $I_0$ = $1 \times10^{12 } W / m^2$ 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 bo5 c tva jb)ww;z;/9ssrom 1.5 min after the planea/ 9 st);c ;wsrjw5zbv passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedbo blr(oo94cg9 cat 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