What is the evidence that sound trav h u,*pl4a(es8:7ot9(4 zeqc ursgr dnjbi 2-sels as a wave?

What is the evidence that sounhu/5.hn 0nblkihk rf (u-j7)ed is a form of energy?

Children sometimes play with a homemade k3 xl9agn cwm5 k3.f 68lsn/mb ae1d9w“telephone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speak 39 kl8. xm/wgn5sada9f6cke1wbm3nls into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do youpo u7rk.duc + 7r2,ype, d:zmg expect the frequency or wavelength to chandk27: p.ycm,egu, z+dru7rop ge?

What evidence can you give that the speed of s nfkif)qolo05)m1a80 wzjwi xj,rty;: c.x 6sound in air does not depend significantly on frequem1:n6o x5y08 w;lx zf )i csaik) fqo.jr,tjw0ncy?

The voice of a person whodvz,pi(uxghz)g)+t n0 h/;xxmv r9m- has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch owuvg w09 eht(/f organ pipes?

Explain how a tube might be used as a filter tmwu 0y1(8z c06os n.viwgvs7 fo reduce the amplitude of sounds in various frequency ranges. (An example is a car 0m06g( n.zyssvwc1 fw 7viu8o muffler.)

Why are the frets on a p .:vfyoou*(7s;i jrz guitar (Fig. 12–30) spaced closer together as you move up the fingerboard toorjfpo : ;i v(zu.s7y*ward the bridge?

A noisy truck approaches you from behind a buiw.gat kozd010 lding. 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 thogk1dztw a 00.e high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” w(sn:ugq-( ojrhereas beats can be said to be due to “interference in time.” g(-or(uj ns q:Explain.

In Fig. 12–16, if the frequeq (qbm7m, wp(hncy of the speakers were lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or closq(hm ,mbq p(7wer together?

Traditional methods of protecting tn 7e (gohm/xhc5h q5p7he 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 ambientq /7h5 pxc7hn5ehg (mo 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 shsg cxs)ko.+qu2 mo6(zown in Fig. 12–31. 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+zsq so2 c)(ukx.6gmo the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift i2:ky:soge7bch7vpe x 1xd 87gk tzq0;f the source and observer move in the same direction, with the same 2kg7; scv7qxo ex dh1y8zekb:p:g0t 7velocity? Explain.

If a wind is blowing, will thi1 z1uzsxh)6 tvut3ej a9tap ;)s alter the frequency of the sound heard by a person at rest with respect to the source? Is thut 9hut131ta )v6 xje z)szpa;e wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monihd6lkf8g- ei;p) deq4 tor 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.;-)f8 6gdhe kql4eidp

  A hiker determines t4 tha 0v;vqbmvvf1 mgs5pv59 9he length of a lake by listening for the echo of her shout reflected by a cliff at thag 5vs0mv9f;tpvv5h4 m b9 1qve far 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 below the waterline. Hebxhv s0x(v j(( hears the echo of the sound reflected from the och0v xv(j(xs( bean 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 does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengtaqz06m 6ggqm-jm2x g 5hs 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 44r6qx ;o t c:.chmbyojust above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fish, 4trc 6q ox;.obc4 h:my   s (b) by the fishermen?    s

  A stone is dropped from the top of a cl+heqxy f.o(zhg:2 d a9z:i( swiff. The splash it makes when striking the water below ah:y(go(9z +sz.d2e hw:x if qis heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to +dee1,5 :.ttfr/68vpcwx zqsc k .bhd84tpzithe ground, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. Howk .8zp4q:tp,cdr18 .tzx/bi6he+se ctd5wv f far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distank* :k7sbz3tl ltc 1m4tus1 6dsce by the “5-second rule” for est 3:tl k dszm uks1*c7b4s6ttl1imating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 120 dit 1nbp.040(xlror bvpz5a d q;lx:i)B?    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 wh th4w9lutn zo- 3hg+r-ak*l0v6or k-j;fm1phose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sounf5lgj.ii. x t3d level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is explod.t3lfx. j iig5ed? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from a,60shkug 3job z((0if. xt+g 2ayxuyfn 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 shut down all but one euut60bjza k( g0hxo i2,gs.yfy(3 x+fngine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noi x0 -b zrtmaerj.;2oa1se 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 for each ata;2b-omjr1exr0 .z device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power outpzk8bgfv l7. 5qut of sound from a person speaking in normal conversation. Use Table 12–2. Assume t.5kzl 8v7bgqf he 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 e;m,m-h4 zg7brgth x.es 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 ampldr)wg am * )o))*i4piyy bc9luifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 ) iobc*wp)lmu4ag y) *ydr9i)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 dBq;m 0ymu24 mib when placed 2.8 m in front of a loudspeaym bum4;mi 02qker 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. hy/+e:u)ecwh What is the ratio of the amplitudes of two sounds whose levels e)uehw+cyh : /differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intenn kvu o pz+4q59l.cq*jsity i c4o+npju. *lz59kqv qncrease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but oivcm y0i7xuz dc)0o9: ne has twice the frequency of the other. What is the ratio of their int 7)yxmccozi u0dv 9:i0ensities?   

  What would be the sounj b e*c7b+qch.vv1+oa d level (in dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 m*ob v1ajce +7+vh.cb qm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seemx49 tx*:i90pxqo u(ha+int qr as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. 12–6.)xr*ua i qnxp+ t4h:0 otx9iq(9    dB

What are the lowest and highest frequencies that an zurzs+qlg d/f 1 c,y+,yuyb)1ear can detect when the sound level is 30 dB? (See Fig. 12–qs/ z+l+1zy u1g,fb)yury,cd6.)

  Your auditory system can accommodate a huge range of sound leveju0qo 6tb3zo7 ls. What is the ratio of highest to lowest intens37zo q0b6jtuoity 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 ojev f5/:qvta*9t zr;.15oikt yq;mrfundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a maikmvfqj; oove/:.t1;9 rtay5r5ztq *ss of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamentalqi i;(fm4wui 8q y)y g t1torjdb0(r:6 and first three audible overtones if the pipe is(wqdr1g8j ii6of0 i:ur;4ttq ()m byy
(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 8 ue1:wd n+u.nei exf gsz35i/top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tu+sf./dine5z:eueg 1wu 8xn i3be?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipey(bitzxb,9q; aq;f1r organ with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes reiqy1zx( tb ,rqfa9;;bquired? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmonic. y2 (m-uxf )uvlje ed6ya8r)+ 4wd o8mjWhat will be its fundamental frequency if it is fingered at a length of only 60% of its udjm2rdv)xju6 aloey )(m +fwy4e- 88original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play (v hd; u:*qaa8t0p z4pbapxl0 E above middle C (33ptpdbx:*8 pz ual 4vha(0;qa 00 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 thx0/sq2yjn; u/2r1atv;ble w n at emits middle C (262 Hz) when the temperatqvt j; /us 0wx;n nar/12eybl2ure 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 em: 0*nvqum. 3a uo+ooat 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece q3r/b0 3 bjxbjof the flute in Example 12–10 should the hole be that must be uncovered to play D above mijb bb30 jx/3rqddle 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 pii7h( rc.m,45 cx(wccq*ptgttpe can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or a closed pip ttwc,rp g5 ti(4.c(*cq7mchxe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at both ends. It resonates at two sw p o-gh p37w()+ vfis:8xjn3nh;yi ppy3i5gxuccessive harmonics of frequencies 275 Hz and 330 Hz. What is x gofi+p(psnw- ii gx3p8h3v );p hnjw5:yy73
(a) the fundamental frequency,    Hz
(b) the speed of sound in the gas in the tube?$\approx$    $ \times10^{2 }$ m/s

  A pipe in air at 20 /e. j 7xaujy.(rwu1ifw 7f7we $^{\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 thepvg;36y fjpas4ebpg wa7nnv0p;u -jnft15( . audible range for a 2.14-m-long organ pipe at 20py.gu( aa n7p ; f-4bn1p5sfnv wt63jeg;pj0 v $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It pbcbh 9(9 :+l23rbp3 zcwnccfis open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the p3+b39b 92hn r clpfbc:cc(wzear 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 adjust two strin:d3a;fh 2t y8p4vaw lsgs, one of which is sounding 2d8 vsthal3yw;p: a4f440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz) m2h 5;4.dqsuu swaq(d 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 m/ u.ifxn- yvur 7;evl rma xoq4;97:( foi:ki(brand X) operates at an unknown frequency. If neither whistle can be hea7x:r:imem n9 ;u u.ifofq4 r (7 li;xay/okv-vrd by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork and 9 b si -yt o4x7a14frm;tbeats/s when sounded witbfmox7;tyta4 s-41ri h a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same freq17jzyvnplyqme4 q- ahpmjs6.1/. 1 kwuency, 294 Hz. The tension in one string is tm-e kp 1qny4z ps/l.qw.67j 1 vmhajy1hen decreased by 2.0%. What 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 qf /zbb*,g ue1try to play middle C (262 Hz), but one is at 5.0°C and the othee bzg1*b u,fq/r at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B hwuyb f+/p81 x-r; q(yap1sonqfi.z )2fl+tmg as 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 oyq)z t sa;(x+wfyi /+bgplf.-18 1qrmfnp 2u 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 personkhbst ed 2b*1) stands 3.00 m from one speaker and 3.50 m from the otheret *b1 )sbhk2d.
(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 suppose (*p* t*1gnl0xd,;zwssurmobd to be vibrating at 132 Hz, but a piano tuner hears three beats every 2s ztxn*b*sw o1*u,0p ;d(rlgm.0 s when they are played together. (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 : 5*xum-yeqe lomk-3tand 2.76 m in air. How many beats per second will k-o 3m5e :* xylt-mquebe heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire enginewo/nxc(4 kv .x fo592f vhel8f’s siren is 1550 Hz when at rest. Wv (/28f4ofhx oe5 kwl9nf cvx.hat frequency do you detect if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a fire engine o:xaukn;x ,h4 hl,6h i1tw/0;kincxdwhose sirexa,n0;h ,;n/ lthuki:h4xk1 w 6ocdxin 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 movi -2z+vbx9 tlrov(g-k prbp4:y ng toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frv xt4b2vlry --9 z(gb+:r ppokequencies 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 s7: x,n3gib jcname single frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hean:n 7 cgj,xb3irs 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 receives the (bg1k h2b6x(;pxnclzd- m4 ppm returned from an object moving directly away from it at 25 m/s What is the xzk64c(x-m np pl 2;1bhp(g bdreceived sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 q3e o-e27lzz*t hs0or l,cb;km/s As it flies, the bat emits an ultrasonic sound wave with frequen;-l e3ezlrb0ohzts,o2k*qc 7cy 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a ta ,5fl* um(tv dvohq7:uba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba hd ul a7o:tq( v,*mv5fplayed 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-fl5 z 8xdxl3ws3,vbxs fa0a m-8jow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissuefx dvx,w8m5a30- ljaxs3 bzs8 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 fjfv,)+ojv v *$2.25 \times10^{ 6}$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. nnt spnks4vg2iz. nx) n8e+6 n;n4-rb When the wind velocity is 12 m/s from the north, what frequency will obser2snx4nise8. ;n6 ng 4)nnr-tv b zknp+vers 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 lanpr:a-0 c aog)npz/iv* d 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 soundn. ox s7ocq;.p3ro mtu x3r:6b is 310 m/s (a) What is 6c;srp.o7 3. ontoqumbx3r:xthe 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 atmosphere of a planet where the saf,42.r maa/yf ughmr9* 8xfdpeed of sound is onrgmd*,2arhxau 9/f.y affm84ly 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 8500p7u,kn *;duat m/s strikes the ocean. Determine the shock wave angle it produu;du* nkpat 7,ces
(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 aj v*bars+6e7 $/theta$ 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 fly:rqmt; g**zcmll 1f m0ing faster than the speed of sound. By the time you hear **0r1 lmmt;:fqmczlg 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 sonar device that sends 20,000-Hz sound pulses dowbyavd2x c(fmkxs1am6+qd) ;2nward 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 puls2ak q2a +dmdf)xvm1c y 6(;bsxes (in fresh water)?    s

  Approximately how many octaves are there in the human audible range fgzil9px k+/9? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It cxdz- 5,j*w edng2njv k l0-8jxonsists of many plastic pip, jd *2enjkz0-jxnlg5vw-8d xes of 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 5.0j- 8sjiyw ;v,4j,9zfxs p: viw m from a person makes a sound close to the threshold of human hearing ,w-jvisjv j:9w8 zpyxi4f;,s (0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sou- hw/w xtv (nw4i6x7zund and an 87-dB sound are heard simultav(6zwxw7/hx-w tnui4neously?    dB

  The sound level 12.0 m f ,of2 ljto nk4cy7zi/)rom a loudspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the speaker, assuminc27/zfo)ky,j4tn l oig it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W outpu+:zo.1pgr 15n.zejma eped2dts3 is6t at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is thetmg o2s .e i+pze11e6.sj :da p53rndz power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear pronb*ecn ;od1 e(v/e t:ytective devices over their ears. Assume that the so/bdc; ye ve1(e* notn:und 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 power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications sys h / 5qjev8l +rs 7m6atv)hm*-m)mmwystems, 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 frz irmyi*,9 l:xequency 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 f an oln1)/ sx8a8di -*n6wmkzhundamental frequency of okhn)6n 8w-/dzms ia8xl1 *an440 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 qck2wezh2/5), se 2sa3nr an fopen tube filled with water (Fig. 12–35). The water level is allowed to drop slowln/52 2)qeksfr 3,e s hczw2naay. 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 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 24tcn9r4qmlafh ) nb55c m*za+.10 g is near a tube that is open at one end and also 75 cm long. How much m5nznac)q *+abrt9f45chml4 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 ri ;1jt 93(zswur(wdvaxm ;9hm 5upb0sesonate 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 n 3ve lpe2me00u k3j3ipd+ 4xg500–1000-Hz range coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the 3e +g u 2p4 0xiejndevm03klp3frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. vu 26 mv65(bukav-8 c sjglonb3/s;dvThe conductor on the stationars( 6;k/vs6nudcb-vvu3 58a lob vjg2 my train hears 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 sshv zt. jializ)/(lu/v/1b3a team train whistle as it approaches you is 538 Hz. After it passes you, its freti)zl1z/h .sia bj(a v3u/l/vquency 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 3nr5d)el3 pb elub/h4just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car dropp)lb3 l he3ru/n45bd es 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 togetheldf7jbrqi ms / 10:rck3*kw7dr, produce a beat frequency of 11 Hz. The shorter one is 2.40 m long.j 1 bic 30rmrs7*:wq/lkf kdd7 How long is the other?    m

Two loudspeakers are at opposite ends of a raila)opb 9ma6 ( -lt0 6s.cswxnqkroad 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 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 hal x0bqco9(na ts66k-wp a)sm.ve passed him, at C?

  If the velocity of blvvs0 7e(85t nn)l :ktg,*geyi *afsis*ydd3qood flow in the aorta is 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 avniee , *7qgys v(k*d0a*fsig3 l8 ynttd:s5) speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s while the moth is flying toward rrc489 u5yqot the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of t8r59qto u4r cyhe wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound pulses as it apprv 1-:5ph u+kfncgk)czoaches 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 tuv1:5kcng)kf z p-+hchat the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signals from h vmxr*+s p 4*b-ms/9guqru9t 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 flatbtuv9h xp*r+ sr-9 /m*mqsu4g) horn. What is the fundamental frequency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be compromised by the presence of0hna r g*46kk(bh9 mjj standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, arjhmbh*k4jn (a6k0g9 nd 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, call. x,zfisljvk; sbe-- 6ed “singing rods,” involves a long, slender aluminum rod hel lbkzi,s ;.-v fe6sj-xd in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made 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 at a fr84rt dt4ly.hwequency of ab wt4r.t4dly8h out 1000 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 Ma 3ycf/)) uk*;k aaj7ac(xabr)ftite 5ch 2.0. An observer on the ground hears the sonic boom 1.7ct jk /;aufb)(rfat kca *x)yia)53 e5 min after the plane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboasq q9o9fdok5 ed+zri2t*.nj0 t 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