What is the evidence that sound trnjik/i/l:ixwf4 n(te:u 0*e 9 zvr0 wxavels as a wave?

What is the evidence that sound is xg naw4)3wxovp8epu216ix+ aa form of energy?

Children sometimes play with a homemade “telephone” by attaching;yz- tdvg3/2ago v+if a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29- + zv g3g;a2io/yftdv). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do zck4--/a; s xhzd-caq8u) pvbyou expect the frequency or wavelength toacb8h adq)--s p u/xk czz;-4v change?

What evidence can you givmafk7 qsw/h0 dq6df+;k-np)be that the speed of sound in air does not depend significantly on frequf)b awnf7/sp qmdd;khk0q6+- ency?

The voice of a person who has inhaled helium sounds very high-pitched. Wr fbcxa wu)jb6ag(70*bxzi+- hy?

How will the air temperature in a irny24xe,r xxgz3;gawy4l,( room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplit50yvxb1p gb8s h)vv c+ude of sounds in various frequency1vcb)8v 5 0b+gsyhxvp ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer toget)u 5e,t.r0 s*hfuy clqher as you move up the fingerboard toward th.5y f uus*e)hq0trl c,e bridge?

A noisy truck approaches you from behind a building. Initially you 6*. du.an7 news(;y1svfe n sjhear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — 6f1svd .s n *n.sejyw eaun7;(you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “inter.mz9yyepw.9g6s:gm r ,e ;ol(ywfu .hference in space,” whereas beats can be said to be due to “interference in time.” Explain9eor pw,yyy6su .lh;g.mg we 9f.: mz(.

In Fig. 12–16, if the frequency of the speakers were lowered27 hjj:6 ijrwh, would the points D and C (where destructive and constructive interference occur) move farther apart jj7irw:hh2 j6or closer together?

Traditional methods of protecting the hearing of -a2g k2n134p3cxbn x wryx3wjpeople who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technologr-bx c 2n3ng x12y3w3w kpxaj4y, 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 as a suwdw s*bg46 q hpuzfe k/7d//,iperposition okihd74 w*/ w spqb/d 6,gufez/f two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and obsexy r8kj.d;* lrrver move in the same direction, with the samer 8;xld.rjky* velocity? Explain.

If a wind is blowing, will this alter the frequency of the s mz6ly6*b gu5w/ 2l+z4nahve hound heard by a person at rest with respect to the source? Is the/ l ey26u5nz6 h4 vwalzhmb+g* wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motkeyz ,09:j+e ex uj/urion 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 reasoning. ux y /uz9+jkr0ej,ee:

  A hiker determines the length of a lake by listening for the echo u,q2l +g- s-vnhr b7)nmfnvd -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 lenf qv-hudnrb--2)l,nnvm g 7+sgth of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship jusc9)n3k4 kxif kt 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 in seawater )f93 4icknxkkis 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air at 2vc717oolc vz04tvu * i0 $^{\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 d 7htnx ;zym30vlw;xg1f0cs,yj 7c+nhrifting just above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12xmnxht;z,n703fyc+cgjvyw l0 s h 7;1–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from tf8-do3-(pmdz 91h)k ji uilxv+e mzf ;he top of a cliff. The splash it makes when striking the water below is heard 3f) -+3ol9j(mp i8z;d uif-edkx1m vzh.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge sto tin j/-cto/q)ne strike the concrete pavement. A moment later two sounds are heard from the impac)o tjq- it//nct: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percentlmue)q 7wy: e( error made over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temp w)e:uel7 (qymerature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level8s sbpo.dp caln t93 ++by(t-y 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 kw*v2nwca o0mx7uz6 5+mm,kh is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a soxhu:m: +tw 86pxo *v6ed9pdsound level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exppehs8 v6 9d*ud:mot wxp6 ox:+loded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four eq -3xeobp3v40vmxzgx(ns2n; z ually noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound lz0xnx;ep2o b n (g3x s3vz-4vmevel 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-,cc(ip 5 n,qnqto-noise ratio of 58 dB, whereas for a CD player ,5 pcinn,(cq qit is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speefd:d1.4z g k4ja:pqc aking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the qce f4 kpjgd.da1::z4mouth. $\approx$    $ \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 strid 13 ,zhxfnx:/i 3nrxzkes an 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 ajperc qj* ,7z8t 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels jc7 ezpj8 q*r,you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registered 130 dB when placed 2.8 m in front oh ;h5.clr +sduf a loudspeh+5d.urhl cs; aker on the stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound level of 2.0 dB. Wha0gm2r +6ah yzyt is the ratio of the amplitudes of +2hy ry agm6z0two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound 42l .bbcj1q ;s ykpw)vknd:q- wave is tripled, (a) by what factor will the intensity increase? Increase by a f4 sl- q p12cbk)j w;nkdy.:qbvactor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twice the frgvu;- z,hqzb zadue6bs6 v3-,equency of the other. What is the ratio of their intd6b h;b-vuzaq gv,u6s 3 ,-ezzensities?   

  What would be the sound level (in dB) of a sound wave in air that c;wrracjj8i7 j* x8bp 2orresponds to a displacement amplitude of v*r;j8 ip7wjxcbja r82ibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level 7jz arz 0)y roayk7a28to seem as loud as a 100-Hz tone that has a 50-dB s)2ra8y7zz 0 7kya orjaound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that ai m;5;e/ ir( gedzsrk3n ear can detect when the sound level is 30 dB? (See Fig. 12zi53 ;dre s /mgke;ri(–6.)

  Your auditory system can accommodate a huge range of sound levels. What is tr.d :5,metv0-d hphvq he ratio of highest to lowest intenp0rqve.- ,m:5dtd h vhsity 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 length+zl.2zk:2nio kvuyl( of the vibrating portion is 32 cm, and it has a mass of 0.3.k2:zz l+ ( liuykno2v5 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are theu(0 sql0 7syjm fundamental and first three audible overtonyq 0us(7msj0les if the pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you expect from blowing across the top o+ f4+k 9v6/aaui(lnn:wdu daof an empty soda bot:+6l (avd aifw49na+ do /kuuntle that is 18 cm deep, if you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pipes spanning 0pmc4 omyw:e-the range of human hearing (20 Hz to 20 kHz), what would be the range of the lenge0:oy- m mwpc4ths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequezy*ar).d c*( g2pnqoa ncy of 540 Hz as its third harmonic. What will be its fundamental frequency if i*oy*z g na(.adc)pr2qt is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned vozop.o 5:im* .hn5w yto play E above middle C (33.izooypvh *wm5n o.5 :0 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 o5,0v3wgjo9*ws f83r eygdp qa pen organ pipe that emits middle C (262 Hz) when the temperature is wvswr*q 380pd3oyge9gfja5, 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 mhdc /b6x//qchr2h e 1at 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece ofzunmzr/ q (n.) the flute in Example 12–10 should the hole be that must be uncovered to play .n(nu)m z rzq/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 resonatjc16s2p0nmh onqd2 7te at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is2jpd67nm2ohtcq1s 0n 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 opelhl z)gocik ezl)+0*m(degp ;5m6l2 hn at both ends. It resonates at two successive harmonics of frequencies 275 Hz and 330 Hzkplg m dl*me2)6e5 0 hozzhlc)gl(+;i. 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 bj y40y+srd;5o/qn,r cxzu: q$^{\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-lk,x6jmh3j (wy ong organ pipe at 20 jm6,w( kjhyx3$^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximatel6(iz)gg ma bdmho34v:y 2.5 cm long. It is open to the outside and is closed av)(h gm zidog436b: mat 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 try. kea0-s phkjasa3 -:king to adjust two strings, one of which issek-.-kjshp: aak a30 sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middlslv v0 2jo:j7jcnh.f46 -frvd e 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) operates5+ dfrbf0bh d 4l(b1xz at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of bfld br zx5hf0 (b4+1dfrequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/0esre,ced;),mp u5eis when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibra5;er ,ed)u sec0epi, mtional frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 ab0 +o8 amtq,kuaag5c; e7ww5Hz. 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: Recall Eq. 115 8e w7b k5gwam0ua, oacq;+at–13.]    Hz

  How many beats will be heard if two identical flutes each trycqk( -wgubyv;,d qtw)(0 jf2r to play middle C (262 Hz), but one is at 5.0°C and f wuv;yjqtd0wr2(qb ),c( gk-the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequ/ 5 it0fz,kb scda94urency 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,5r bu/aftcsd40 zi9k 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A person stands 3.00 m from one speakrt),mde ch0n,lsux28 kn(d o2er and 3.50 m from the othe o2rntl m8,d2 ds ce)u(k0,hxnr.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating at lpx-hsg u 5 1-gy;)aua132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together.a x;u -gg1-5yl uha)sp (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 wavelengths 2.64 m and 2.76 m in air. How many b (;/k nx;m1l-qmvfgrz-7 aeebeats per second will be g bz;rm7a;x-l-nke /q(mfe1vheard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire enhv-)e 4r v25dw3uxjvbgine’s siren is 1550 Hz when at rest. What frequency do you detect if you moved eh2w3u) bvj-54v xvr 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 enginevml t *co) m6wz)d/ fnxik5u-0; ikxsv :ney4. whose siren emits at 1550 Hz mo6 n i4fk:vkc o/u)vlidmx;5sn-tz xey .m)*w0ves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in mhm29lpu:h537,juw sgg6ow yfrequency if a 2000-Hz source is moving toward you at 15 m/s versus you moving towar,mh93gm5u wj 6g : pysol72whud 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 the same single frequency horn. When one isbe o9.s la4kcs,,a 5o*8ybzt2ite)w j 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 freojzs yotc 8, b9,k24eabs.ie 5*at)wl quency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and op0fg:ugah+-g q s*o 5receives them returned from an object moving directly away from it at 25 m/s Whafgo a:*sq ophg0u5g-+t is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/f c g:se 06o4dyzf ht /xph/)lgfq(,6hs As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency doehoygglx hc:pz( f6 t)/fq60 fs4ed/,hs the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba wamo c 45b5 apjja-7jz+os 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 heard if t oa475m a5 o-jpjbzjc+he train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound wr+yupxy6 7)h4i*md qcaves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and thed x6iqrmyc*yu)74hp + 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 usxj8lcx bpq+l7 jb-3 z7ing 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 vely5dwv8w -ce *9nhodl 9ocity is 12 m/s from the north, what frequency will obsd 95o l eh8dw9-vwcyn*ervers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if i q: w +3x1:bkhyf,x9flzsztjwq9jh.;ts 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(mb8 kd(igp6j z7d7wq (a) What is the (mdz dp7qw6i87kj(gb angle the shock wave makes with the direction of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmospvq6 9ux an1oa9p 0gqi8here of a planet where the speed of sound is ona9oi0x 1uq8p9a v 6ngqly about 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s strip3jte 3pe f aw)kn3at,hm jg;5:25xxckes the ocean. Determine the shock wave angle it produ3 5fxg3hewj;e2m, pkxp) nta5 jta3:cces
(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 jylc5:+rqg .y4khq j6jtu5z (f7e x7 d u+q,kh$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a plane exactly 1.5 km above the ground f5h f/3ac6(en za6a3 h3qaxtzblying faster than the speed of sound. By the(a33aza 6hfc 5b3qetz hx/a6n time you hear the sonic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 12–34. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a s,hfxzpbk 32i ul(r5 s9onar device that sends 20,000-Hz sound pulses downward from the bottom of thezxp 5bh2isu,r39 k(lf boat, and then detects 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 octaves are there in the human audible ra*saxw/nze) gev 2hs 13nge? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display gbf pj-1hn,ygue4p 63called a sewer pipe symphony. It consists of many plastic pipes o6y-f gpehjn4 p1gu,b3 f various lengths, which 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 make-yvw9zlk1 5 a4ob)jic s a sound close to the threshold of human hewj9z c4baik 1-5olv )yaring (0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-if .wqe3wzu5p4x6q5/skyq m * dB sound and an 87-dB sound are heardmup35k.z/se*q6 f qyx4w 5wiq simultaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in thaxyb.qkh9su/h 9( rv-e open, is 105 dB. What is the acoustic power output (W) of the speaker,a(- ux99qhv.hrbysk/ assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The power output drops ubofu2(5hy 9f tse6-rby 10 dB at 15 kHzts b -u(u65 2hfr9eofy. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear prote0/vuk .7ogkjg5np 6c zctive devices over their ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the 7u6j z0k/onv.gcgk p5 power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications sy4-o tpplx0 ts/lv1ho +stems, 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 freqvq7 zu7cp4uqcl )nsun0/iq 8- uency 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 between fixed points with a fun+c4yoyw *1d0/ndl:wpz7vwg r damental frequency of 440 Hz and a mass pe:w+yl4*cdyv ron7 zw 01gd/p wr 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 viyotc 31b+fql )bration above a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to t1lb tf )3+cyoqhe 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 nea-wuw .y.el tzw7ikx1 -r a tube that is open at one end and also 75 cm long. How much tension should be in the string if it. -lwwu7y t ie1kwx-z. is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate wi;my 1wu2s r6as 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-Hzxs,wz ;vz(c )b 6kg;cg range coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than tcgb( z;6 ,gwvcxs )z;khe other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The conduct:z p 0qq6b.twt6f(xrr:d )dw for on the stationary train hears a 3.0-Hz beat frequency when the other trairp wd x:rwzf6:t0tqdf) 6q(b.n approaches. What is the speed of the moving train?   m/s

  The frequency of a stewx g7p2sr)z 5f)uyg-mam train whistle as it approaches you is 538 Hz. After it passes you, its freqz5u-s))2 wp7m x yggrfuency 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 liste( .ostso g.n:ining to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound i:go.nsso (.tof 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 bo lk0;+oig hc)5qv-o yeat frequency of 11 Hz. The shorter one is 2.40 m long. How long is the othero-lv 0c5 o+ qohg)iyk;?    m

Two loudspeakers are at opposite ends of a railroad car as i(*s/g+ 1wr 6mieaav oet moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listens from the position A, in front of the car, (b) he is between the speakewmai1 *a+erevg6o(/ srs, 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 0.32o, xxxl c48k2uw iu)bea2e+f 7 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed alo)xc wa24le xu be8ou2+k fx,7ing 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 2r:lvkfym5f 2 moth at speed 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 kHz. What is the frequency of the wave detected by the bat after 2kl f:25fr vmythat wave reflects off the moth?    kHz

  A bat emits a series of high f-z0n n3iyc m9e1 bjxv*requency sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each jx 0-vyinzb31 *9cemnis 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 onc 6 oj2u* ez-8d4kpg uz9htty,oe used to send signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long hornsg-ptt oou4h*uz2e9zd yk8, 6j 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 tube.

  Room acoustics for stereo listening12skh-pa)ubb j 4dk5 v can be compromised by the presence of standing waves, which can cause acoustic “dead spots” at thhv41 ku j-s5k)2badbp e 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,” inonql/)wflr 5b (0p)n svolves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hfn) /n)0lrblp( wsqo 5and. 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 he yj27y ul6;suiaring for the human ear at a frequency of about 1000 Hz i2yuls6 iuj;7ys $I_0$ = $1 \times10^{12 } W / m^2$ 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 a c4thi yvbfg /y5h(/ *ozhxh yc4a6:n5t Mach 2.0. An observer on the ground hears the sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s altfgy5 zha:4n/( y oct45bxhic*h 6hyv/itude?    $ \times10^{4 }$ m

  The wake of a speedbosva l +l 77n9j-gq3zj(dh;jgwat 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