What is the evidence tanx0 qb5bt6kgyka -xd (j80f+hat sound travels as a wave?

What is the evidence that sound is .c ,vwm4mct4q a form of energy?

Children sometimes play with a homemade “telephone” by attaching a string to o6lk*a: i/ zhothe bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly/*ooh:ki l z6a how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you expect the frequ7k +7ww pmyd-j4 r-2 gqo(wjqmency or wavelength to yqw7m2r wj7q-mop+kw (jdg 4- change?

What evidence can you give that the speed of sound in air does not d q s56s,8ck,k*xkxx1fgg-i mx epend significantly on fre, k8 *g1sxx-xq5,skmci gkf6xquency?

The voice of a person who has inhaled helium soundj.b ahf)ym 0m)s very high-pitched. Why?

How will the air temperature in a room affect the pitch of organ pip 8etlw g(lre0g9rtw )-es?

Explain how a tube might be used as a filter to reduce the amplit5/up2 7*ic x:o ovmhs. mxyma dz(96csude of sounds in various frequency rangei65(pom xacmm*:z hyvsds7 /cuxo .92s. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) i. ud2j) jhbjtt 7q*y*kf88a0jwrtt+ spaced closer together as you move up the fingerboard tob+t*dfqhyj.j8ar* kw t t28 tujj07 )iward the bridge?

A noisy truck approaches you from behind a b2ny oq3r3g*jk uilding. Initially you hear it but cannot see it. When it emerges yrq*nokg33 2j and 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 said to be due to h n 3qeb7,o)ahmp 7,plre4+ gm“interference in space,” whereas beats can be said to be due to “interference in time.” Explair ahp+lnme,)73,7eh qp 4gombn.

In Fig. 12–16, if the frequency of hwa(8pc*bi*4cl 1ewcp14n s1q u er,tthe speakers were lowered, would the points D and C (where destructive and constructivetccs*ewi1h lwqa( peub*n 8 ,11c 44rp interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who work edqs+ -ofeyir2n yyj2 3jl.*. 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 hy. *3-2.+j2lerynq ej od fsiyeadphones 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.1 lvxd0*y,vz9mmi3eg 12–31. Each wave can be thought of as a superpo vl1z,9mi x0d3ve mgy*sition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source andr hlwrv n1z7 y/7x+n0k observer move in the same direction, with /lrkvn nrw+77z10yhx the same velocity? Explain.

If a wind is blowing, will this al8ntrrbt.yh+n f4su /) ter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or veloci8yhnt t+fn4b)ur / .srty changed?

Figure 12–32 shows various positions of a child in motionbarpg 8m s8w25akpi25 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 chipgm5iarw2s5k p8 8b2ald hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the e9jyfgs3uf+csiab( 9 2dyq1 f:g.k.yccho of her shout reflected by a cliff at the far end of the lake. She h csidyc:ksfbgfy+q.9jy ug3 a9. f(21ears 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 waterlssb:x5 1/g9wfvvncd8ine. He hears the echo of the sound reflected from the ocean floor directly belowg/f 91vd:nxsvb8scw 5 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 in air at 20 yn7s ; dt4nu+:bjj oqq 6+jft8$^{\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 m9ebd5 dq3v z8*dl4t u f;mrf;is drifting just above a school of tuna on a foggy day. Without warning,ldq rm9zefb ;8utdv;354*d fm 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,    s (b) by the fishermen?    s

  A stone is dropped from the top of a q9:rzo)c o/:hk, gj xicliff. The splash it makes when striking the water below is heard 3.5 x/ir )ook9cjqg ,:z h:s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike thp +jv)dcb ukf i4 ath11.ts2p:e 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 u4:ab+ vtc2 sipf h1)pdk t.1jare 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made okpds+pu,,1 u mver one mile of distance by the “5-second rule” for estimating the distance fromdm+ ,p,uupsk 1 a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity ofx -nkiiqa axh:i;+d a25q:g*u a sound 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 s/qsm-0 kz3c r0r bl8lnound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneoffufm,2 5cqwai/ju hkd 0awnh( /6j+ 4usly at a certain place, what will be the sound level if only one is expld 4amhca /fwwuj0f25/hq i,k6ju n(+f oded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distan(-b y0dk jyva1y58s3vbmhe3 4in) gqqce from an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down al5dmv8bys 0j1 q4n(3by3h) gky -qiev al but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have mr0gvu,arsank 72b b5*d1m6q a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What ia dbmq5arg n67s0vm b,2u1rk* s the ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speay b0xr*:l( zwaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on ay:( wlz b*0xrthe 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 eardrum whose hl4o)n vzn2ap b-ii 9-pb c24ahh+mb: .cy*wu 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, whi(;muu fqro3 9dci ql(1le the more modest amplifier B is rated at 40 W. f3(uuq;q r1i9( cold m(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 regkl*v73efbo-j j.t0 biyc6l 3 eistered 130 dB when placed 2.8 m in front of a loudspeaker on the sta lc biveytb.-0ke6jjfo73l* 3ge.
(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 4gxi(oyi p2-la difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ 42l (ixyogip- by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor r1bma ao (;;xzh0 f z4rxqyu80will the intensity increase? Increaauxqa0 rh8 ;(m140rz bzx y;fose by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudeh 3:q +ox9omris, but one has twice the frequency of ther+ix9oh 3m:o q other. What is the ratio of their intensities?   

  What would be the sounu+o/u3c: 9vcy;t tzko d level (in dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz? ;:/u+9u occotyvk3tz    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100- 5wclx 57ycv+v/qh3bm Hz tone that has a 50-dB sou5c +hql5v bw3xc7v y/mnd level? (See Fig. 12–6.)    dB

What are the lowest and hi7mgzvjxij;nj*6 f *7 ighest frequencies that an ear can detect when the sound level is 30 dB? (See Fig. 12–6.) n6gi7fx mjvj z* i*;7j

  Your auditory system can accommodate a huge range of sound levels. What is the *4y1kvu71npzde u:vd/ru k e2v hs; h+ratio of highest to lowest intensity at h snr1+ 2euvkyk7d:1ezdvup; h4/*v u
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violifpxjwf9 db )r51en -6in has a fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass ofdx n965b f-jfi1e)wrp 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and fih9/xrc0u o,w 48xvgyvx9e9o uc*j5vy rst three audible overtones if x v c99urxvc/w*0o y x5ge8o9 ujv4hy,the pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you /d2-.nass ca sexpect from blowing across the top of an e.a/an s-scs2 dmpty soda bottle that is 18 cm deep, if you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ*r tt-c d( hg5g: ryo9l0sv5il with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of oy 5l rrs:g(c *-gltd9t0ih5vthe lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string hasejr0lv ,dx5n; a frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its ori0 dv;,xnr 5ejlginal length?   Hz

  An unfingered guitar string is 0.7:y+zxfvn 9a :rl+n3* qst)kv 9,getld roi8n 23 m long and is tuned to play E above middle C (3na9zf,vn+3:lid 2ko xq*9sryl t)r e n:t+ 8gv30 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 middle C (262 Hz) wh,q btgo8zh+i4hezl-4 en the tempe4+il bezhg-8zo4qh, trature 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 rtkks6 a21m;k20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthj4a2jyz.7oo+qi 8nozin s , r2piece of the flute in Example 12–10 should the hole be that must be uncovered, ijoy.4z n 7so8zaorqj2+ 2in 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 pipe1e-s omzsa *-v( qrp(v can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. 1(soev*rmz -(avq s-p (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. y,wnxdz,3t5 s80 m long is open at both ends. It resonates at two successive harmonics of frequencies 275 Hz a3, wdnsxy5t ,znd 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 pt6s s hfomw3j(hwf a-+aq30 6w)*jgi$^{\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 ww (+q5awnnu9,a cqhi.ithin the audible range for a 2.14-m-long organ pipe at 20a (9. 5auqh,wnwc ni+q $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is apprys+d)lv(u+lh+y v4 byoximately 2.5 cm 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 informati+vyv()b + l dsu4y+hylon 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 tg9(uknl mjj07wo strings, one of which is sounding 44g(k 7jmj0lu n90 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequenq u0uxj a;u4fdx v/)rx55racyi;zu74 cy 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 operates at 23.5 kHz, while another (brand X) operibxa op-ae+31v7 of/ frf9w y)ates 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 playedbf)37f1a 9p eiwoyfro-xv a+/ simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning i 3;9cjeybp y+fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explaine ybc+9;3 ijpy your reasoning.    Hz

  Two violin strings are s(un8 ;:/*knihkl xog tuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the /o*8 gxk;sulh(kn:in beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if/ md. ls1bymm; two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and bd;1m.sm m /lythe other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forksh:)+ .puw7x4 iitv meu, A, B, and C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency oimw7h x+ ).tv4e u:ipuf 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat 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 spen-w3y 2ehsfz 9 6ioe4baker and 3.50 m from the othyb2oe w sf9nh34 e6iz-er.
(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 vibratit8 mii8 p)y +zn wn0mg:l*e0 q1xvm9ukng 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 13my08 w v8z1)ie+nx*li m0qpk m:9ntug2 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 wavelengtk,j,6gv,r zc4 hd)ng-2pjq n vhs 2.64 m and 2.76 m in air. How many beats per secong,,kgh v rcp),46q -dn 2jzjnvd will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire7h:ni ixfh b,u-of+ *r engine’s siren is 1550 Hz when at rest. What u ixf7, b-:i+*h fhrnofrequency 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 whose /rc npl-h4,k8 lezvk;siren emits at 155-l nekch/;pz8 lv, kr40 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 moving towawu q-p*zdhr9-rd you at 15 m/s versus you moving tpqr dwz9-uh- *oward 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 th,z asvh+ o 3+bga rr.*tav(a3he same single frequency horn. When one is at rest and the other is moving toward the first atts roaz3ha,h(+* b+a grav.v3 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 5n405+i/aom37tcser i -cm jtr0.0 kHz and receives them returned from an object moving dirrr 0to/aiicj-s 35t4m+n7cemectly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at (ljujkim-52 ca speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency doj5 liuk2cj m-(es the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original ppqvm4- ,pvbb.6- hklDoppler experiments, a tuba was played on a moving flat train car at a frequency of 75 Hz mkpbqv6,p-p -l hbv.4, 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 ultrasououuztf4 70i+y nd waves to measure blood-flow 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 What is the expected beat frequency if blood is flowing in large leg arteries at i7o zft0uy+ 4u2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of fyqs*5 r r;6yvnrequency $2.25 \times10^{ 6}$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 isy h4 aly7e4c0j 12 myya74jl4 ec0 h/s from the north, 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 ogpo5qoc6g) w x+ 9jj*rn land if its speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 whereb z6 yss76s)auqp 07t *4eajkl the speed of sound is 310 m/s (a) What is the angle theq0y kzelsja sta6*s7b)6 p 4u7 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 speed of sound is6-3t jh il36y zdwc5gu only about 5i c6h6yzlj-u wt33dg35 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 mdfvr ri (b8, e,u;s/jf/s strikes the ocean. Determine the shock wave angle it v; eru(f fdj,i8brs,/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 mtynd (6a5 .1ej d0nox$/theta$ 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 aboci h 7x d 93lsi)yxf0)qoc5b)ave the ground flyingbix c q35l9 ao)c)hd)x7y0 isf 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. 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 sonam2muw/anoq 6 )gj x(elvaw w7dx(341dm e1o9rr device 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 designed to work is 200 m, what is the minimum time be o awmmx1xe6 /wjd 37oeg4uvdlr q(amw91n()2tween pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible rangvp4i() kgg6 )ppnu+y fe? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe sufpta44 qg g*,- mb*knymphony. It consists of many q*-f 4t,b k*ugmna p4gplastic pipes 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 5.0 m from a person makes a sound close 4jmq)duy93 d lto the threshold of human hearing (0 dB). What will be the sound level of 1000 suu 3l)dmjy4qd9 ch mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-day*r)j0fbn +zw v;h k rjad26;B sound are heard simulta2k0aj6w;j nary ;f+ v rbh)*dzneously?    dB

  The sound level 12.0 m from a loudspe+ e:tv9d3b ovjs8s,afaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the speakese3j:t v,o9s+fvb 8adr, assuming it radiates equally in all directions?    W

  A stereo amplifier iss4 zcpf 8.c)mu rated at 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power output in watts at 15 4c ).fzps mu8ckHz?    dB

  Workers around jet aircraft typically v8ft53 r jbq:+i0f nynwear protective 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 powen qf0 v+8fbjn: 5ir3tyr intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systepua,b)7f3g v*f egkv 8ms, 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 akir3,jvs c3r6 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 withwoct; gh1-17 hb9waqjy : q(bvj8 wtq*,fo;vs a fundamental frequency of 440 Hz and a mass per unit leo 1bqh j7ws;9ajco8*tywtqf;b -h:w1vvqg ,(ngth 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 i58h.4g geko uhnto vibration above a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the a4o.gke5 8uhgh ir 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 2.10 g is near a tube that is oped* 3apb7l; t5o j0gisxn at one end and gtjld;a5 *bsio3p0 7xalso 75 cm 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 2pt-5 b+w a :7pyzdxzj-zeq3 l+b qxv2observed to resonate 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 to( c)+5- m:*yzie.gjult ijgjrne in the 500–1000-Hz range coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves abo*mgj.-c:lug+z (y etr j5iji)ut 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 tu8b5xs(use l1rain is stationary. The conductor on the stationary train hears a u5euxsb l 8(s13.0-Hz beat frequency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle q* o:ylqy0y )mas it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant velocity)?l:)y yqo *y0mq    m/s

  At a race track, you can estimate the speed n t /l . +au21.navbvn21irkrtof cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the strailr11 ik.b tvn .n /u2n2r+tavaghtaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 62c-nfpp bygg ;gx j,d)4v1nr11 Hz. The shorter one f4-g;vn ,jxp)rgnyp 26gdcb1 is 2.40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of a railroad car dhimv3w *+amuxx24 b2as 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 freq2m m4i3 h*ubvx+2dx awuency 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 normally about 0.32 m6h+u s7h ,acrvvju no)rd,;*v/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the horr76 sua,h*,dcvv;nj)v +u 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 mothtzzmi)wepz .o3:7 q51 kqmqu, is flying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. Wha w.m5quq,zz17mk3 t ie)p:ozqt 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 sy q/:g0nfu.c aound 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 one chirp returnsg uq. anfy:c/0 before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) vc9j-bj m:9w2 s r00ehremtkeqn /54gwas once used to send signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to cre eb2 04k ewm9e-/q9jj:tnrmh 5r0vcsgate 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 listening can be compromised by the presence of3h x*n scx 7z4xz59edh 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 frequencies cx45ehx z7d 9 x*hz3nsfor the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, slend +)ckhso a;u/yer 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, ringikcyu h;/ )s+oang 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 thrrgub0x; :5 bdoeshold of hearing for the human ear at a frequency of about 10b x;b5rgu:do0 00 Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observ yhq( q8kz n8:liwp:r4er on the ground hears the sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s w8ril(hy p::z84q nqk altitude?    $ \times10^{4 }$ m

  The wake of a speedboat lcr+3e a9am8mhfs6y3y yzk2 8 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