What is the evidence that -/lg9xo1hc ,e) k thgyewj8opkl2*i0 sound travels as a wave?

What is the evidence that sound is a izs r8 v ,hsxff oi,wu(x ip(d19s29u9form of energy?

Children sometimes play with a homemadeo.udoil -mq7s2dyd, j/q sfw q-w6x; . “telephone” by attaching a string to the bottoms of two paper dw2dsoixufqwq;.q 6s,o7m. l -j-d y/cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes frotgo.;: )4meauqa* t ntm air into water, do you expect the frequency or wavelength to ct* )tgouema. ;tn:aq4 hange?

What evidence can you give that the speed of sound in air does not depend 4qxfbp nj. rh5/els )2significantly on freque5 2/.hxfnpe4)lsqbjr ncy?

The voice of a person whx 1rp 2z1lfn0mo has inhaled helium sounds very high-pitched. Why?

How will the air temperatu myvlvo 3/35:k6 ropayg *ig:rxw2ou4re in a room affect the pitch of organ pipes?

Explain how a tube might be used a6uww4r6b0nb vnea ir(8ooh + )s a filter to reduce the amplitude of sounds in various frequency ranges. (An example is a caab(uo6+ hb)iv68e0or nrw4nw r muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced clos)cdyfqn6jquf a+- -l 2a/we 6c dd9v(ner together as you move up the + aqved6wacyq)f2-9 cjnd6-un l(/dffingerboard toward the bridge?

A noisy truck approaches you from bec,h3g :85vfh kw tic+m1ugvm:hind 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-f3tw+ vkg8:c vchiuf mm,1 gh:5requency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,,,cn x wtlx1jz .dv97f” whereas beats can be 7ct,l1 f xw,vxz9 dj.nsaid to be due to “interference in time.” Explain.

In Fig. 12–16, if the frepl o(e :lzl2lfh0asef7j:ql2f7 4t g)quency of the speakers were lowered, would the points D and C (where destructive and constructive interference occu 2 l:jff plq2(zht07l l 7l)efogsa:e4r) move farther apart or closer together?

Traditional methods of protecting the hearing of people who work in areas with vp) xx nidzgam)nf :6f*j2-u k(ery 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 )jmnx:f)ku2 fi*n6d(zpax g-, 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 shofw*yb8wk0 tdgnk3c( 7 wn in Fig. 12–31. Each wave can be thought of as a superposition of two sound waves wi *w(db7c8wyft03 g nkkth 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 3an1oa w,nph 7 sl9iungb/1d2 if the source and observer move in the same direction, with the same a27ip/nd 91o, lunn g13swhb avelocity? Explain.

If a wind is blowing, will this alter the frequency of the sound heard by a 3 z(kkqtv 6 jj8h)9om)oj;bp sperson at rest with respect to the source? Is the wavelength or velocity 3 v8b)o j)oq zhts;(6kmj kjp9changed?

Figure 12–32 shows various positions of a child in motion/hn.c68ps fw h 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 ren.hw sh8p f/c6asoning.

  A hiker determines the length of ae 5c5kg o d;7pkoal85z lake by listening for the echo of her shout reflected by a cliff at the far end of the la agodp57ko5 lc5ze ;k8ke. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side *qq+ 1 uae u cfj3)/whjm (u.n*pl.jjaof his ship 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 in seawater is 1560 m/s (Table 12–1) and dj) lf /ujq *hq1a*.ew+jjm (un.pcau3oes not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air at 2ld5g9/ k a1yki0 $^{\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 school o f m-fxg7qxv+b3 cc;k (h0iu.4xx7 b03 cxnzukf tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km awayq cu x fbf7gn+7x;0cx.i 3 0um(x- 3v4xkckzhb (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 frv4jirw0; , ip gpvhx6p-le7j+om the top of a cliff. The splash it makes when striking the water below v, ipxj;04v+gi-hp 6ep r7jlwis heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stonhfr93,l 6 womcy-z *xie strike the concrete pavement. A moment later two scy36l zix*-wm, h9ofrounds are heard from the impact: 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 percent error made over one mile of distance by the “5yyf/nqz(s (-vp ge/ s7-second rule” for estimating the distance from a lightning strike i(qv(spysz/g-7 eyfn / f the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound h zih4lys0o 7n,59cyf at the 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 inten(8ua bn: uwnd.sity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fwxxrt )z( g1 nlh40rse/cc8a1ired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, n841 crc xgs(xne0zh1)twl a/rot dB’s.]    dB

  A person standing a certain distance fb4u m :b bu.xaal,3uen4pd);arom an 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 captain shua4eubd) ua3:m,u4.n bbal ;xpt down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a sol . uuawvi.n: 9pol;df7fqx4b +6 .lbignal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise ff7+xi d6v4 ;l .q a:pu bwo.9unlof.lbor each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power outputl pp bef8xsbybo+1 86; of sound from a person speaking in normal conversation. Use Table 12–2. Asp pbbol1 6b;xsy+ e8f8sume the sound spreads 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 strik: 1eg; dwdnra1es 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 at 250 W, while the more modest amplifmfd3a*//75uple78 oylzbedg ier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a l8g*pa eom/7zy bl 3ed f/du5l7oudspeaker 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 met:3raht st z 8/7 9vscmdf1,g:uon2yvper registered 130 dB when placed 2.8 m in front of a loudspeaker2o 39st/t,yvchd 8szvpra:g n :f17um 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 soun(vh rq.:ozpzg2/mx*lp 5qi s2d level of 2.0 dB. What is the ratio r2 5*v sp lmpxz:.2ho/ qqzg(iof the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a soundx:ysxz35/dn qa78+ ,c+ b otr7eef oco wave is tripled, (a) by what factor will the intensity increase? Increase by a facy fq538+/ccooxxrz+ b,d77 e an: eotstor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudeej/ b +*bmr.3v1powza s, but one has twice the frequency of the other. What is the ratio of their intensi.poe/b *j31raz +wvbmties?   

  What would be the sound level (in dB) of a sound wave in air that correspondc-n v+fi:qq )apl: s3ms to a displacement amplitude of vibrating :)vq-3la icqn s:p+fmair molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as lou, rs24d hudywdy 415jad as a 100-Hz tone that has a 50-dB sound level? (See Fig.rd wy4ad h5d ,4s21yju 12–6.)    dB

What are the lowest and highest frequencies that an ear can+dcy ffqqd4/5:5ysw b detect when the sound level is 30 dB? (See 4+ /:q5syydf5c bqdwf Fig. 12–6.)

  Your auditory system can accommodate a huge range of soud8 b,g- w6ia z n8uscry4m2/dund levels. What is the ratio of highest to lowes4,-z6b8miu 2yw/a dnudsc rg8t 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 gw+,g lb a /)6vtio*blof 440 Hz. The length of the vibrating portion is 32 cm, l+v*io, w 6a g/bt)blgand it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first three audible .5po 3hpk:f enovertones if the pipe p.:o5 kpnh3fe 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 w2 im* g;):yml tk th)d-c/0srndqbl9jould you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if yo:;9 2b/sl-tlit*j c)mdd)gqknr0mhyu 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 span3ru(2 bjkk7y* ncng2aning the range of human hyck 23jkra*nb7gn (u2earing (20 Hz to 20 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 theh1d,fvu 00fjvs0w 1n ird harmonic. What will be its fundamental frequefh1 1 s,fw 00jvvnude0ncy if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m e*j6+ yj wi8amlong and is tuned to play E above middle C (weayjj +mi 68*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 an open organ pipe +c+y5p w fbr/gthat emits middle C (262 Hz) when the5py fcg +/+bwr temperature 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 at 20ph- ,4j67ymu dlnkh m+xem;9q $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Example 12–10 shodpg:jqy9q 05s x 1.kqkuld the hole be that must be uncovered 5x90gdy k.qsqqkp 1:jto play D above middle C at 294 Hz?    m

  (a) At T = 20 $^{\circ} $C how long must an open organ pipe be to have a fundamental frequency of 294 Hz?    m
(b) If this pipe is filled with helium, what is its fundamental frequency?   Hz

  A particular organ pip.1mnp yq;jm 95s /hxtee can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an openj9/h nm;1ty5 s.eqpmx 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 u f e k:vru:zs2le,3h7at both ends. It resonates at two successive harmonics of frequencies 3vsh2l,7:u:r ue ek zf275 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 eqjgyoi; 0gu 3.0f (xt$^{\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 ph*mto8 54cc13stwb8sktsh9hl 8v lq+resent within the audible range for a 2.14-m-long organ pipe at 20 cs8w 5c+8*t48ttlh bqm1ls ohk v3s h9$^{\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 the outside an8l z0z2d0yv1rq holyhl6q3n) d is closedrohl yndhlq63)0zq2l 0v 1yz 8 at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to adj dtpr;5g3tzv v5m0* quust two strings, one of which is sounding vvgqp 0mrz3 d ;*5tt5u440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 H(cgsgv3 / 53wded5wup z) 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 whistl)jz+:s0 :udcqvuxd n5e operates at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate cudn )us0+x:q:zjdv 5 the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning forkh9l,0e wkkh6 i and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of w 0ek,hi9hk6l the string? Explain your reasoning.    Hz

  Two violin strings are tuned to tha9h hg..xoh7gge mn 0dix3hpi n66a)8 e same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played tog6xiagi 6 o8)3 mgn0nhh..9x 7phh aedgether? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard ifmv k sm-idu+y37. ox, wdpzf) kr/th3, two identical flutes each try to play middle C (262 Hz), but one is at 5.0°Csrm,tfkhydwv)7x +. p,uk oz3/i-d3m and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, anvbt,v- w 5oi9sd 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 vi-5,stwv ob9 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 speakenfun. 2 ab2;jer and 3.50 m from the other.2nuf j.2nabe;
(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 h 7/lnqb)-/.z gps(cu 3igft x132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the-n uzgtsb.( g/cpx ql/f)h3 i7 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 wavelengta:(a nijw 4)ctyeg8;r hs 2.64 m and 2.76 m in air. How many beats per second will be heard? (Assume T = 20ntea48 jyri(:wg)c a; $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a cer vaxu:/1mm yn.tain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 3u xym1n: a.mv/0 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you dpsz:5f5 uonkejv -,uxfk 7 ;adv9-j+ uetect if a fire engine whose siren em-jx+v9u jovu5 -pk7fa5 sed,fuzn :; kits 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 sourc-5gq+a tj4 )zis5hk .5b0kwmlelk hi /e is moving toward you at 15 m/s versus you moving toward it at 15 m/s)ikm0gh w i-5a+ 5.bql4sljkt 5/zkeh 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 frav xop,zowy3g)*w ; 2requency horn. When one is at rest and the other is xy w)3o,avp2 w r*;zogmoving 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? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and recedp.u,ix,sz 7 xzc 5l8jives them returned from an u ci5,p 7 szdlxx,jz.8object moving directly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it fliesazli, 9g ai2q1, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave? z ai2aliq,g19   $ \times10^{4}$ Hz

  In one of the original Doppler experimentsrn*5x9tq(h0. q sj;ui a 5a4 fxhipx-a, 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 frequencu*p ia55a0t ;f4h.-qx9axs h ixr q(jny was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to mee, w5xr jzw1,3eb juykm8 cbp:/fm) 4dasure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of syr8c,m/jxbmwf u3b z,d 4 1:5wke) ejpound 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 frequency prqdy,twjr0qr ; 3 wvo8 )*a,yo+gdz5 $2.25 \times10^{ 6}$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. Whe36 vs*y6psp hl5,5accxzl1 cr wfk;7 en the wind velocity is 12 m/s from the north, what frequency eh;sa 7ps16c53clr 5*fpz 6lwcy vk,xwill 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 mov8u uu,10bub5jhdce z 2ing on land if its speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where the speed of g u (lte4 kmp4q +;ph;orsiks qo40i18sound is 310 m/s (a) What is the angle the sh44ip;kk;pr4t qimoe 8hs( q ug+1sl0o ock 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 atmosphere of a planet where the speed y173ji j o5fab(m .:k mtbxb3tof sound is only am.3 :13kbo i b7mtxfjj(5btya bout 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s strikes the ocean.)py94ry+y2xrr7 o rbb Determine the shock wave angle it p y79yxr2o+ )p rryrb4broduces
(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 .wwr9igq ;,6sct 3elyc(-gqe $/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly over(2 nr)agu wl e3fx9p4chead 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 h 2 we9lc n4p)f3au(rgxas 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,yg2 4iblr, y9eba.qxau f.6n6000-Hz sound pulses downward from the bottom of the 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 wag 49fre 6bxqy .ab, l.iun2a6yter)?    s

  Approximately how many octaves are theree rgqs:xarsf m .p(:b+u15 *bf in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphon26 tmhym1 f2l)8,clqjr5d dc7 usg y,dy. It consists of many plastic pipes of various lengths, which ared85tsu 2yq2fmc7ld cm6 h1j,, gldy)r 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 pe94:tj c1 r km4xaozgn4rson makes a sound close to the threshold of human hearing (0 dB). What will be the sound level of 1000 such zo4g9jx:4n mkt c14ramosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-d8z2:x256+ow i1rxj oyq sxu;ytruiq+ B sound are heard simultaneousy526 y2ou8w+;:rzxqiq rs x+uxijt o 1ly?    dB

  The sound level 12.0 mo0gprxq 2ngtxra 3)r1k53 vv 8c70hx i from a loudspeaker, placed in the open, is 105 dB. What is the acoushri02txcqvn75 0go8 3r3x 1xgprkv )atic power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rafvua591y8po ;p t lxf:ted at 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power outpu1f t:al58yx;v pu9pof t in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over the.e dizb2,- ibeir ears. Assume that the sound level of a jet airplane engine, .2 dbezi-be ,iat a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communiv+hw y ollk)mluv0;l z+y*h l(8 c)(gxcations 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 freque*8f4fe n 1/*fw zvr4wqjxl,w9uqr/f df yc.)h ncy 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 iu b349a8ztor6b enz-x)6y s ubs 32 cm long between fixed points with a fundamental frequency o ea3b9- xb8u64tyzbo)n 6urszf 440 Hz and a mass per unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration above a vertical open tube p 65zm h, ehb5d9tkbv2filled 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 t,2h 9db5hbp6e k mzvt5o 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 t:c-tck qju7y 0ube that is open at one end and also 75 cm long. How much tension should be in the string if i tyqc:0-ujk 7ct is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate8gj q(1rqv*ydmz33t m 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 rang t*c7fp vpvy;0e 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.ypcv; pft07v* 34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The conductozelpqznsm, 5 oxf: d,)y8ou; ,r on the stationary train hears a 8x,;ze:5sy fnq , zl)oo,pudm 3.0-Hz beat frequency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a styzdirtahm:o w, g**) gi0- lo+eam train whistle as it approaches you is 538 Hz. After it passes you,wha * ilt,zdo om giyg-+*)r:0 its frequency is measured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can eukslt xpoe(3r 6+cs9 9stimate the speed of cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency hal trs(6c 3xosk9+leu9 pved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, soundi*hocj p2k.k z:9 itw/rng together, produce a beat frequency of 11 Hz. The shorter one is 2.40 m long. How long is p 2.9c i:ro/k*ktz wjhthe other?    m

Two loudspeakers are j x 4a6c:hkty7: o4bc+2paoy vat 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 212 Hz, what is the beat frequency heard by the observer when (a) he listens frv462+ 4chc :ao 7jykoat xy:pbom 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 is33 yu ufgd6v5n normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a 5nuy 3v u3fg6dspeed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m3zn1hljjke -6/s while the moth is flying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 j3-nzkej6l h 1kHz. 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 frequency sound pulses as it624uh-: u 9blabu7z vg,rqqht approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp returns before the nex7 ,barh u:qgzvtub4 q9u62 -hlt chirp is emitted?    m

The “alpenhorn” (Fig.fer94tqd /bq l0f/:dnd kk( o) 12–38) 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 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 od0k obt /derffqnk(/:9l4qd) f this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo lxlov;q6drl( zgl3c:h wc5) 2jistening can be compromised by the presence of standing wave hd(;lvg5: l)6colq xz23wcrj s, 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 in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” invf6 w6sts5 y-ziolves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice,ytzw5-s6 s6if 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 human ear ak3ql;m:ig tn,(o m0t: n*cb+lh0fg k,exx-cgt a frequency of about 10gcg q:ohn : kkt n0,itb0gx*x+l(cmm;3f-e l, 00 Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on the groun aqvmns7q +w90d hears the sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s altitude?q9 07wnqa v+ms    $ \times10^{4 }$ m

  The wake of a speedboat is 15 ep+m6 qabs4a, $^{\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