What is the evidence 5s ),,fafy ctahh ;d(ka1w yx0that sound travels as a wave?

What is the evidence that sound is c: l kbqyme:zogam ;j 6:52i.ua form of energy?

Children sometimes play with a homemade “telephone” by usvv;p+ +l;fr*m 1ef lattaching a string to the bottoms of twofv r*;+mllsu; 1p+efv paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passi vn03q.0 7liqmsf xz)es from air into water, do you expect the frequency or wavelength to cha lnvf30qm70 )qs. zxiinge?

What evidence can you give that the speed of sound in isrgdgan :1 d;) -2ujnair does not depend significantl g js)1 nnadgi;ur:2d-y on frequency?

The voice of a person who has inhaled hodb+5l( q6s +*vvhx lhelium sounds very high-pitched. Why?

How will the air temperature in a roboe( gxr1y20zmt, lj/om affect the pitch of organ pipes?

Explain how a tube might be used as a filter to redum elxf) 4z /eucr,+v8kce the amplitude of sounds in various frequency ranges. (An zx+ v8fkc/elmreu,)4 example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together vf6(y.sv tsjmm99 r;r as you move up the6vmv.;(yfjtsr s mr99 fingerboard toward the bridge?

A noisy truck approaches you from behind aq,a(s;i -,auc v vkhht3a .u+g building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 onk ic-qv ,,g;+.a( as3vuuhtha diffraction.]

Standing waves can be said tmk i1 h9.db643pnnlja o be due to “interference in space,” whereas beats can be said to be due to “interferebap j.lhk469 md in3n1nce in time.” Explain.

In Fig. 12–16, if the frequency o( ocb jsw7e9a5u;z 1lzf the speakers were lowered, would the points D and C (where destructive and constructive interference occu ob7j1z( ls;zaw5 9eucr) move farther apart or closer together?

Traditional methods of prote.g 4nl ou;tme)7r.2(b+v dyjvma 2mij cting the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in additiont)2lm a i.jv4u7o jr ym;( dv.gbem2+n to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12y 2 hbd.*t4yq8ijfo)b 18ojif–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the twoo oy)b* iqbj t1h.f284y ijdf8 component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift ij(xgbfq- x(p3 se8s)c lq:s1i f the source and observer move in the same direction, with the sp3l 8xfi-es:(j) c1g s(sqbqx ame velocity? Explain.

If a wind is blowing, will this alter the frequsdg,kwtdg 91,esu9 *hency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocity cha ,de*g 9hgd uw1s,kts9nged?

Figure 12–32 shows various positions of a child in motion on a swing. A monmjdrlu.;7md8gfwv)jm4w. o( itor 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 yourduj.w gl( f8m7.rom )m;djv4w reasoning.

  A hiker determines the length of a lake bu4v5pxn5 vo+ia a7 :axy listening for the echo of her shout reflected by a cliff at the fua 7 : niap5+5xoxa4vvar end 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 bekio9 b89 .:h0ynqiw -i dstre/low 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 poiw9y8di.: /ie0qh oktbs ir-9nnt? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengt99gka 432ulbxxdb nc(( haogh:;6njbhs in air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is drifting just above a school of tuna on a foggy day. Wikisl695x nppg8 hw, +dthout warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How6xg sp+5 nh9dpk ,8iwl 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 when s 8ji ,a:bgdvm2triking the water below is he8j:,d2m gbiv aard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stoneqhmn* ;+ x4bgu 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 1.1 s apart. How fahmg*+uqb;n4 xr away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made odpp pb+7s,41nujg ,u wver one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperat jpp+4 dwsup 1b,g,nu7ure is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 1)05 hh bvauly+( ljzjy(j60gd20 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 intensibf(s fvuv. 3;jty is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired siwjv, 1qy4wy f8multaneously at a certain place, what will be the sound level if 1 wfwyjyq, 4v8only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certsbm(b*wdxm s.6we 7 yb3pwkku7a *(v2ain distance from an airplane with four equally noisy jet engines is experiencin6kwxmwsaky7 pb(u 7e2m3w(bs vb.*d *g a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of *, vslbie 46gh :rccb(57vr;ap fael+58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the backgros 4b(c 5p6r+ vfre* b7,vhaacl;:i legund noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a pers kt qs::3sdx45kqv;i zon speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the4q3i;k qstsd: xvz k:5 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 s dmc 5 vk/0( * 46abz3rgmyz+cc/irccrtrikes 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 m8zcxelm/z :je qd yq8g;(o-6g ore modest amplifier B is rated at 40 W. (a) Estimate thj/- ol8 emq (;ez6ygzg8xc:dqe sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter*,u/mni c e1mr registered 130 dB when placed 2.8 m in front of a loudspeaker on the stage1/unm c ,er*mi.
(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 typical07ma6dha zv,d7* bnml ly detect 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 Section 11–av, a*d6ndm7lz0 hbm79.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor n +*sz,(tv6cjp7 lm kdwill the intensity increase? Increase by a *vd 7 nsj6pzcm+,l( ktfactor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but ow5 ggzx/ecc+.f3h3 cz phy w*5ne has twice the frequency of t 5. zch5zg+3c3we/cfg*whpx yhe other. What is the ratio of their intensities?   

  What would be the sound levelh57s-ef udpttn*nfwk( lba 7(zw27s 1 (in dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating ail(ek7w( 5w 7bt 7andsz1fs np-*huf 2tr molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-gzpc) u+ n8bvk1 *lfd,Hz tone that has a 50-dB sound level? (See Figlzp+f1c8nd bkuv)g*, . 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect whe;ikc-yyfeg62wikkf lzu-xp34( g*2 u n the sound level is 30 dB? (See Fig. 12–6*ku-iu pfgl3i4 w 2k(6-kfzcex yg2y;.)

  Your auditory system can accommodate a huge range of so jqqm5h1oq twwd:o*10und levels. What is the ratio of high w1:qhm1qjoq d0*t5woest to lowest intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental frequency of 440 Hz. The length 1jyvl xjr: np( :a5d0xof the vibrating portion is 32 cm, and it has nl5 x( 1:0aj jpr:ydxva 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 rie 7 +wkay3/yaudible overtones if t/ayyk irw7e3+ he 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 wiocxyylz** j yks7r0. 8.4ldwould you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you ascr. 7y ilk4woz0xj*ld *ys8.ysumed 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 piu4( cl sp6t)p7wqu) c fguau81pe organ with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of)pt8f 7 uu1p64a) wscu(lgqcu the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency oo a ieud08(2nof 540 Hz as its third harmonic. What will be its f0i(oun2 eda8 oundamental frequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tunek5 4qrkut6un m6tn+8 ed to play E above middle C (33u68n 65utn+ mket4qrk0 Hz).
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that emit q i79x w3u/jnsp 82/ce-axkbys middle C (262 Hz) when-ejs p3y89nqwx7u/i/ 2 xckba the 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 25w4 :z 0b tfjkzwjl.l:0 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flutl 82j lsnvuwety z+3h*l (muv(myr ;7;e in Example 12–10 should the hole be that must be uncovered to play D above middle C at 294 my3lwh2u+e jus 8* (;mvy rn(l ;tl7vzHz?    m

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

  A particular organ pipe can resonate at 2qze88yo2se3zw86g j4 is6r/jy7y unw/udh + f64 Hz, 440 Hz, and 616 Hz, but not at any other frequencies ine8r / iy28eo 7 zfyg6qwyzunu8s46sj 3jh/+wd between. (a) Show why this is an open or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 kb;y53 fdxx u9m long is open at both ends. It resonates at two successive h 5;f yu9bkxxd3armonics 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 y p11ho2y3zdd $^{\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 pr5u ( tzwn*;n v4yck9xlesent within the audible range for a 2.14-m-long organ pipe at 20nwzx* v k(;n9y5u cl4t $^{\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 and aotsp.ik*4e b8 .5dm ct k xkwvp/6:v.is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of your answer to the information in the graph of .kw.vvidm.:ao c6px8 p* /ks tk4b5teFig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to adjux 9cq0lyo6;f pst two strings, one of which is xyp;96lof qc0sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency vi re*lyw 63v5xdv0u6 if middle C (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle opera,ex t/5oi :y9oofuvxgtrorp p*61/d4 (w vcc1tes 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 vxcd1/xt (ev4g p,f o1ycow:iupor/r6* 5t9othe operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s w 5 lg dpu2bxn+dzd5+(jhen sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork.5+5xgnd(+ pdub j l2dz What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension in one vr7ajy:ofu05k 5fu :estring is then decreased by 2.0%. Who :u7vfe r yfaj55ku0:at will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each q3+x7hsm l,.h;(o8 wkyeb(t5wnnt pd try to play middle C (262 Hz), but one et dsqx.8b o(wmk,t ;p7ynn 3+(lhw5his at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forksrk aew-.5c09iw8ib 0v ;z) bz5 ozw oul.:ouec, A, B, and C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is 5zcukae;o5890.bu) -:wrwo ciz zi e0wl.o vbheard. 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 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 speakeeasfilyq+v tg*)i2 )e vltk0n n -g-7/r and 3.50 t y*ig-t/s) vvl72f +g le)inakn-eq0 m from the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrat8w.ckvum1r3v1b89t tx cfcacuk (q*/ing at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be tkvxv1(fccaq km1 uu. bt39*8/rcwc8 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 w gpb6xc+ qjf v;* r.(le ddy-prl3/vn1avelengths 2.64 m and 2.76 m in air. How many beats per second will be r q.fl*-;/d bv1pn3e6 glvxc yjp(+drheard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain firehk/dwb 5+g(s/rfnl 7e e fg-6b engine’s siren is 1550 Hz when at rest. What frequelr -beg/wf/+ 5nfedkb(sh6g 7ncy do you detect if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a fire engigs 0 tbz2wyxvl(4e3 hx.e4v 2kne whose siren ebxvzx4sv(e.0g2ylw4 hkt23 emits 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 movin2df+mys+2rl k)m m0jmg toward you at 15 m/s)+rmj+y2lm m2md0 fk s versus you moving toward 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 s5gqdugkv 2*,i u4- k-2ji fkv/bha4d uame 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 b4fv2k4*jghk,-dv-5 kqa uui2u dgi/ 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 recei spfyp)q4k3y6ves them returned from an object moving directly away from it at 25 m/s Whak) pyqy436 fspt is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s Ab-ugfuk:pg2 a7i7, e; tl9sabs it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency doesegb;,7ga9t-: l72pus u kf bia the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler e /gx ;q :wdn1iy whl(mla.+ky,xperiments, a tuba was played on a moving flat train car at a frequency of i,qkxw.mwnd(gla 1;:/+ y lyh75 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 of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeds. Suppos gr r+g+3 ns,75ugnss,irdo,eup ,c3se t 7s+n3,rd gsuu5 ing ,+epsr3gr,o,s che 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 ultrdn)rg gpm+wr:o2uyl. i) .y0basonic 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. lfad. zbltd7t8 9 8gq)When the wind velocity is 12 m/s from the north, what frequency will observers al8 )ltzg.td7q 98dfbhear 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 its sp jpmbn ig/,d+p;k +l-6-+qji fo wgn6qeed 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 wher z -h2r7kkt.l,;uybnn4m qv 2le the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of the airplane’s motio42y;klnv b.7mk ht,ru2-zq ln n?    $^{\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 isxftx 30beiegn /;s;1lpc40)8s l wkmh only about 35 e;se 4g n;i3stmk0lx18x l)f/cb0hpw 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 th+e, 4.nv.hflbnp9w3b j5uf z we ocean. Determine the shock wave angle it produce49l3z 5wfjbvbnpw h.n uf+ e,.s
(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 .bnu+w)9 nb thn+q nj,)u *m53vnaq ay$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a p0 :d*ezac:r+gcl olw* kv /+jklane exactly 1.5 km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 12vzdk+ k: 0j: *racllw+ogc /e*–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 sezeh l*7(hlk,7n w*hflku* yt 1nds 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to hz*(tflw*k1 l7 k7ny*elh,uhwork is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how man.-jysm :r(wos y octaves are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer p-avwz;acbiy6rl( 1k. ipe symphony. It consists of many plastic pipes or-z.6blwkc ;( i1a vayf 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 makes-* a;t*b /qbf tmt5mdp a sound close to the threshold of human hearing (0 dB). What will be the soum/b a;*mftt q*5 p-dbtnd level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dBq5i;:s+dyym d sound and an 87-dB sound are heard simulyy+m sdq: id;5taneously?    dB

  The sound level 12.0 m from a lou x 0jku3f.g)3y ecg;dcdspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the speakedckg y0efg; .uj33c )xr, assuming it radiates equally in all directions?    W

  A stereo amplifier i i, )lbnvq 51qel y/d,ogo7am(s rated at 150 W output at 1000 Hz. The power output drops by 10 dB at 1 5(qllmn,d) qb7ov1a g/oy,ie5 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear prj (r/+ k if)an:lri6vmotective 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 wj)6(m+af: ilr rkin/vould be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications s5ex5xqscw+14 lr c+7h (tg 9hdd zqjs3ystems, 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 tuxog .ar2l zf,5tt;z7r1x d03vqx4o ovned to a frequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 30/ +b(ldr1waq;jm g0zvj:suc s:kl. a2 cm long between fixed points with a fundamental frequency of 440 Hz and a mass per unit le+( j 0qu/w rz1ks;0vd csl:aa g:.jblmngth 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 vertica 4:mpr3i*ap;vd jk ,fal 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 l a* km,dpavr;3p4ifj:evel is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of+ zh.k,5ni dkz mass 2.10 g is near a tube that is open at one end and also 75 ch ki kz,n5+.dzm long. How much tension should be in the string if it is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one full zfd2z,geld+jf y6 .:q 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 from v6ajm a)8hmt5ujf-;z 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 ) mf;zu65jth a8vjma-farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train isgtcl,8zg) ;c m stationary. The conductor on the stationary train hea,g8mzc;t)cl g rs 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 steamq abnz uvd/9z9q ;e5)n4oe6 l4e bvhr4 train whistle as it approaches you is 538 Hz. After it passes you, its frequency is4ebr4qd9z/n54a u;b6e v)l enhvq9oz 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 by8j,x ux- q,:4aptotje 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 halved) as it goes by on the straightaway. How fast io, qtj a4tju-xp :,xe8s it going?    m/s

  Two open organ pipes, sounding together, produce a beaw iy*i4nlyf -v)b 8/bn-ab.a et frequency of 11 Hz. The wb l)bb 4 fvniia--.y/en*a8yshorter one is 2.40 m long. How long is the other?    m

Two loudspeakers are at opposcf.k-h fwtvrpradcr5 :2y 24x m- t.4u(7yb ngite 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 th4yf mtar 7dpw: (cbn -5trhu.c4r-k v2gy.xf2e beat frequency heard by the observer when (a) he listens from the position A, in front of the car, (b) he is between the speakers, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in the aorta is normall8mq5/kp;a7y)rtz vuvy about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound wavesv kyt;/au )vp7zm8 rq5 were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s whjq(:6lpp.l.kmxaxs )v(o sb0d 3fm 2kile the moth is flying toward the batok :q6 p2p m0j xlk.sd.absvfl ((x)m3 at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequen,xy,u x(*hx di b8bv7acy sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo from vd,u,x h8i7*axb(yx b one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signfg hrd3nvh)m.wr955nals 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 fu5h.)rdmwnr 9nv3ghf5 ndamental 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 listen;a:rzn r.)ds9j*+aagw (diwving can be compromised by the presence of standing waves, which can cause acoustic “ n.r;+s avjg r()w9*wad ai:zddead 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 ro ;r u7fj3hf;hvds,” involves a long, slender aluminum rod held in the hand near the rod’s;ur7jhf; hfv3 midpoint. The rod is stroked with the other hand. 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 heari*gvzdg+rd:7m j , m5 0hibj3;2poawjing for the human ear at a frequency of about 1000 Hz i2gdhivoi :b,m 5 djm3;w0r*+az j7jpg s $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on h7my 92gwp(6so2aib:pbctb +the ground hears the sonic boom 1.5 min after the plane passes directly overhead. What is the 2a9wp +7bsbp:(cg6yi2 tm o bhplane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 155-gb42 ktdd jl $^{\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