What is the evidence to 9u:hxcvoj;7gc h )yk-s)m;zhat sound travels as a wave?

What is the evidence that sound is a form of energyhl z8 vc030eqq?

Children sometimes play with a homemad 6d53r u+cg603/lpwkgdm4dwnolu+ow e “telephone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into oneo d+3 d6ngk 0mlwo wpu 3/ulg5c+6rdw4 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 2mi(h3 9z+ frqjt p d(:zm9clyyou expect the frequency or wavelength 9l i +cq3f2mhd zy9(mjz:tpr( to change?

What evidence can you give that the speed of sound in f/cv9 6c3fo 2+ ntmj3ghn0 bdeclt :)aair does not depend significantly on f3e cd 0v6 lf+ mt:f9canc/hjnto)3bg2requency?

The voice of a person who has inhaled 8ey:+ -xmcgyhca3 qf(o3x3y ehelium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitchjiyy u:p0ps+ 0 of organ pipes?

Explain how a tube might be used as a filter to reduce the ampliteyw)4ud-9f:xn hkd+55 b cwfj ude of sounds in various frequency rang:wkw5d)h -5enfyf49 j +dcxu bes. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you move upz ) iq2jl 5emgw+cxnh8 l43:yl the fingerboarx4hymg i5+jnle :328)cllq zw d toward the bridge?

A noisy truck approaches you from behind 16wc orc (k+q3 jnx6yxa building. Initially you hear it but cannot see it. When it emerges axy cj(6w6o1nxr 3kcq+nd you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be sa v*u;hf7ink5g:w/axir 4tss 8id to be due to “interference in space,” whereas beats can be said to be due to “interference int gxi;i/ 4 kw 5af:8vusr7*shn time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowo78juhv i5;kzbr4ll + ered, would the points D and C (where destructive and constructivej +zr5 48iovl;lbhk7 u interference occur) move farther apart or closer together?

Traditional methods of protecting thea-,n *p co ql4qw4hnm/o+1cno hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levep4l+n*c/ waqnoc o4 qmh-n o1,ls. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12– zh0k7wy ezs0k yk4 qp.bk7-:w31. 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 two componenq:w0k7y- hbyk wpzs47z .kke0 t frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if-jpmc*t 4 j,( rpx5s+xzty:prf/ u *ityh7o7 z the source and observer move in the same direction, with the same pzxmi+5p*x7tt:p,-j rjufyz r4 (yt/ co7*shvelocity? Explain.

If a wind is blowing, will this alter the frequencmw hd18ebzc 9f)7 cfgm tln31rok8,3 zy of the sound heard by a person at rest w1kg3r9mm81e3fd8 h oz7,)wtb ncfz c lith respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of u ,w-mo1p5 i eswj3f)klq 5q2ua child in motion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your ru, q5wuis21eq-of plwj3mk)5easoning.

  A hiker determines the length of a lake by listening for the echo of her iy/ujwvm +c6 -/de+wsshout reflected by a cliff at the far end of the lsyw+med+jcw6 iuv/-/ake. 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 trdy/g- 8lgaq i9.bl1g he waterline. He hears the echo of the sound reflected from the ocean floor directly by grd19lb-q gig/a8. lelow 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 wavelengths inj(e3ksd7 rbt5vl w8u6,hl +pjxj7 rd) 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 tu0h)h. fy:yi zwwd38,;hlgnmk na 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 (ag0 hwh wl,y )8yn;:. zmkfid3h) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes when strik /5 6+w8 fg7s02zw n kym8epnsvklpm/oing the water below is heard 3.5 s latek /evl+y s/zpwkn7 ofpsw882 0m5ngm6 r. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge sto n ,d60nf1nz +.bmvjxone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels .n6nxb+v0o fz1n, mj din 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 bysz .y,x lg) w+fj) 7qhekqv)h7 the “5-second rule” for estimating the distance from a lightning strike if the t xzef7,qjq+h7.)yl vhgs)) kwemperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a u8tgz/ g4bej1( 4vn jasound 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 whfk2 f5y/oww l;ose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simulta /fht-fmqq( ipnb)czo4u +0j ojwm4;9ao9 f+qneously at a certain place, what will be the sound level )mcf p+ta;/wf9(+ jom09j4qfqz b i4o-nqu hoif only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance ff/am+ay *f t -,b+tkyojs/6enrom an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would thisa/te -++ykjff,/bo* asm6 ytn 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 58 dB, whereas fz0qks v )q ;4fo/wvi2cqc1kv 2or a CD player it is 95 dB. What is the ratio of i2 o24vf ;qizvqkv/ck1)cw 0 sqntensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from 3j wh8x(:hwbea person speaking in normal conversation. Use Table 12–2. Assume83hx:bwh(jw e 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 strikes an e dhg/9hwwnl9 e6p)p,gb;na/ f5 uxfu5ardrum 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 amplifier Bazh)s1o 2g ff9 is ratfo h9z1)gaf2s ed at 40 W. (a) Estimate the 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 +b5ucwx.mjx ileh.t 0wx:a63 registered 130 dB when placed 2.8 m in front of a loudspeaker on the st.mtcih6wxx b5 a3ux:+jwe. 0l age.
(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 sound5nkny-wk1(l y o9; u(i*o6qjg +fabu e level of 2.0 dB. What is the ratio of the amplitudes ok(q+ lyuna9 (o1ujyb k* of5 ;ing-e6wf two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave istu4 lq9rp2p;no9h 8;r* udv,gpd sf/ l tripled, (a) by what factor will the intensi9nu;grls8qdlvptdu f*h ;4,rp92 p o/ty increase? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displaceme,z2u zu,l(tk0 scs.d vnt amplitudes, but one has twice the frequency of the ok,vl( zd.cs ,ut02uzsther. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air thascr sflc -/), wn1c)lx(dgu.lt corresponds to a displacement amplitude of vibrating air molecules of 0.udclc,x.n g- )/f )wc(rlls s113 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seemkx9hs qj.7 kd yv,g5(;aghti2 as loud as a 100-Hz tone that has 9isk(qkj yhtv hg. d xa;52g,7a 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an earnfs2jvncv no v,;; .h+ can detect when the sound level is 30 dB? (See Fig. 12–6.) ,.vnos c; nv;+ vjhf2n

  Your auditory system can accommodate a huge rang4q q t4/ xcqb3ctqb0y1e of sound levels. What is the ratio of highest 4q0q1qcbxcbq tty43/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 H4gtohu)-aoq /ja80e0qm3 vlhz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under wh lht-qa 340oq/vm8 gahj uo0)eat tension must the string be placed?    N

  An organ pipe is 112 cm long. What arei: 4z n 5jw/jqslpi: :tqt-ro8 the fundamental and first three audible overton z:i:t8p -wrjols /q: 54jtinqes if the pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant fr(xcmppz 9dg-; equency would you expect from blowing across the top of an empty soda bottle that is 18 cm dez(9pdp-c ;m xgep, if you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pip yg) (zkmu,a vs55idbg:n3kis99oj 7ies spanning the range of human hearing (20 Hz to 20 um7oy(iz, )id 9 ass9jg5bkngv i:53k 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 third harmonic. xqkizr x3s2z t(34bt 8What will be its fundamental frequency if it is fingered at a length of only 6 brst qi 3z48xtxzk32(0% of its original length?   Hz

  An unfingered guitar szv5 5ebnrou60tring is 0.73 m long and is tuned to play E above middle C e5n z0r65vuob(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 that emits m j0)p xx9usl .nat;zdeb,cl 2.iddle C (262 Hz) when the temperatul9. )pes;.xtc bln,ua0zjdx 2re 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 0 9dp yvt5 (d:bo(t o ou,f9edh+aq3rv20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpie8 w;bhyds*q :nfbc3 v7ce of the flute in Example 12–10 should the hole be tha7c :b8 nvdfq3w*b ;hsyt must be uncovered to 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 pipe can resckh) btl7g0z+ onate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an ope lk bg)h+0c7ztn 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 lo z0in,qf/m p 2)qt0)kufa* hx ii*won1ng is open at both ends. It resonates at two successive harmonics of frequencies 275 Hz and 330 Hz.),foupqika/nq*hm2tx*f 10 0nw ii)z 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 6/ tnjxgyzd+-$^{\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 tl*m3 wt /7pyv yv2 4ywvc)+jzahe audible range for a 2.14-m-long organ pipe at 2 ypc 27+3v /4wjvzm)aywly tv*0 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cmith+h uutck4j137n 8 v l7w6wx long. It is 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 ear canal. What is the relationship of your answer to the information in the graph of Fig6+78j l 3u1uctkwxh4nvw7 t hi. 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 stringsbni s-(y *ifx*gj3p t7, one of which is sound(x*pi3jgn -7fiy *tsbing 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C j9v,zgyf (at0rvorr.wza1 71 (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while another (br*m.+fpgkrb(8e5mtap and 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,rm8pmg(*p etkfa5 +b. estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when souncw: w 2-xwwij4ded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain:xiw -2 4wwcjw your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tey .a 9k+pmv0zwnsion in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.] w0kpaz 9v+ym.    Hz

  How many beats will be heard if two identical flutes each try to pl0hdj +u o cwsjg( i-e.3/su5lway middle C (262 Hz), but one is at 5.0°C dglo3(i5/0 .w-h +scej sujuwand the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A1bo /fn 8svs*sx-r2ie, 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 heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What-s/ s 2rsn 1fxivob8*e 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 b j4ei7 6urcr,3.00 m from one speaker and 3.50 m from the oth4ru7jebi ,r c6er.
(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 2wo/ a ydlub;x6e q3;ybe vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 sx qy63/waoulyb2 e;d ; 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 and 2./ melj5p63we zg4rcw .76 m in air. How many beats per second will be heaw 3 rc4ze.plmgw/j5e6rd? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is imxw;,p;ur2 p1550 Hz when at rest. What frequency do you detect if you move with a speed of 30 m/, w2ru;m ;ixpps
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a fire engine wht2v-qhl)m1a n ose siren emits at 1550 Hz moves at a speed ofn-hv2q1 taml) 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 20yfslku+f*q88 t 4.+ b4zrra6bl6qs jj00-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exac.6brq8lutjs rqa f bkj+4yzslf6 *8 4+tly 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 :tip 2pzsc83 59kwwmykte ru7e *y9. yfrequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What.*rtcs:ye9 py5w2 i3p keuk9tmz y87w is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultr)6qrn:;-yxdm2 cn5,p jjceg*auvz m :asonic sound waves at 50.0 kHz and receives them returned frodj2mny qr mvc x5:,c)-jg u*pzn e:;a6m an object 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 zl4 7sel s 40udy;ed)uflies, the bat emits an ultrasonic soul esyu7 se4d 04lu);zdnd wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, hp aw9(skd t8506fkpfa 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 frequency was heard if the train car approached the station at a 96 5kwfsfd (8 p0akpthspeed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow s 5 6f5btovr3j 3:cnycap efx4t0g.8z speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s Wh3c0jx5 v3r.:o8pf 4 et6zgc5saf tbynat 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 frequeny/.; 8wvm3.a v7m8ox6lkqa y v1oggu ccy $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequency 570 Hz. When the wind velocity etx1 ro(e am/gi 3;kq8is 12 m/s from the no xr qg;okm(e31/8teai rth, what frequency will observers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land ify,9l+:1gozj/c h pz 7qkj ye;s 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 .n b5z201i21kzl mye x+bg8pibdiu/qspeed of sound is 310 m/s (a) What is tb1.zde+122xiygpub5nikz/ 8li bm 0q he 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 auh4mi2t ecc5mn-f93vtmosphere of a planet where the speed of sound is only mtmh9 2 i35e-uc vfcn4about 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 tosv (j9u0a9g1x)mt - tb ipa3vhe ocean. Determine the shock wave angle sup )90b1mg v 9vj t3o(aa-ixtit produces
(a) in the air just before entering the ocean, $\approx$    (Round to the nearest integer)
(b) in the water just after entering.    $^{\circ} $
Assume T = 20 $^{\circ} $C

Show that the angle kr licl0fsee+u lq5eec)), as9y,0j.$/theta$ 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 fl f:)8txno2k idmt.qv0-u4wejifa l-6 ying faster than the speed of sound. By the time you hear the wut2i 6v i faxoe):fdln - kq0m-t4.8jsonic 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 de+a.j ey99hm (+rlvnijsiu 8e 5vice that sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is desigs ve9lnha8+jjeur 9+im(y 5i.ned to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible ap3w (r,xzyy tf7 6wg(range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe syaae0 c1 y 7 m1erqtvf+y,d1l0vmphony. It consists of many plastic pipes of various lengths, which are o 1e+, 1 ec afqd0yvv0r7ay1tmlpen 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 per(vg+j j -: tj:lg9nwggson makes a sound close to the threshold of human hearing (0 dB). What will be the sound level of 1 lj-(w gg:ggjjtvn+ 9:000 such mosquitoes?    dB

  What is the resultant soun-o t+t g6idqz4d level when an 82-dB sound and an 87-dB sound are heard simult+ goz6d-t4i tqaneously?    dB

  The sound level 12.0 mq53ippq47kmv from a loudspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of7kqq v4i 35mpp the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The power output 8p.ufk(fowww0 2 cnd1 drops b18 d(f2op0wkcnw. fwuy 10 dB at 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protectivef zq+a);0w 6;pksa+ )k dxayok devices over their ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the power intercepted by an unprotected ear at)ap qs0kzkykwadf o +);6;xa+ a distance of 30 m from a jet airplane engine?    W

  In audio and communications slxv ar0 7wknnc;4 gejs9 ,q.)nystems, 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 lic. 0/dht)i yxt5: ydc,e r:vto 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 32 cm long between fixed points with a fundamenta/cl0rre 6mq/c l frequency of 440 Hz andmrc0rcl/q e/ 6 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 a09z j 8gcbjhtmj-a yfd7e 7;x;bove a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tunin xaz9 b7jygj;ej0-mdt f8;7chg 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 tube tyki; q5oej i+*hat is open at one end and also 75 cm long. How much tension should be in the stri oiiq +jk5y*e;ng 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 ff+l f hok 4 ffu3.bkp(zcfs :ext6/5 1n5t3eicull 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 two sources. Themp5*qnm . jbx rb71jr; 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 minimalxnj.q 1jp;5rbrm7bm * 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. The conductovk(-2afi:z )b pghc0w1a)3f+29 hcibbw x pbmr on the stationary train hears a 3.ah2c2wz-:i1(bav)0wxmb g3 fpfb9 h+)pkcbi0-Hz beat frequency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a stel2kjmzp)fm0/ kd/k d +am train whistle as it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How l+f/ k0k mp z/2dmd)jkfast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars justt d jn(ykjor/94m)yb* by listening to the difference in pitch of the engine noise between approaching and n d*yoj9kyj4tbr (/ m)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 is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11 Hz. Tm /er9rl ps52htws /.rhe shorter one is 2. lmstpse2r5 rh./wr9 /40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of a railroad car as it moves past a sta/f dq r7)9eqah* 7cmiationary 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 froma9hqi)emfar7 7 *cd/q 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 2x7p2 1 f4vxq q7;wcnonw-xtwnormally about 0.32 m/s what beat frequency wonwc o7x wqpn1xtfqw4x- 722v; uld 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 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 mo1m t*3jge;xxia5 p v*oth is flying toward the bat at speed 5 m/s The bat emits a sountjio1g3 * *e maxxvp5;d 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 frequency so )02+0rv ycx oxmi/xhdund pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and e/iyd+xxxhv2 c)o00m r ach 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 next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to se0 / sv5aels7wwnd signals from one Alpine village to another. Since lower fr/0wa5sesv 7 wlequency 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 of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listef+6,yyry 6s;mk /t dccning can be compromised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamental frequenci;yt ymcks/ f6r6cdy +,es for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, ca4g(1( l g,+xqh uhil pl2uvuay 9;.ewjlled “singing rods,” involves 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, the rod can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-c jglyv xg2u(lu+h (w;u,ip. e94h qla1m-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 frequency of24t;azbjf*n. ombmw4 abom;t f*nm 2.4zabw 4bjout 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 Mach 2.0. An obs5;nk uuv9y6j0 u* jbphl7v(iz erver on the ground hears the sonic boom 1.5 min after the plane passes directly overhead. Whatyu(*uv9 l0k5i hn 6 jjz7vup;b is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedbo daksz.w5 5p*0f76rf 0 geifbaat 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