What is the evidence that sound trave9js el*w,4s,lwb jo ;inich )+ls as a wave?

What is the evidence that soun qv.j0-w:fqup d is a form of energy?

Children sometimes play with 3pnm 4j8wtk(j.wxzxy *p 0-av a homemade “telephone” by attaching a string to the 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 how the sound wave travels from one c v40pztyjj-3w xw8(m .kn *pxaup to the other.

When a sound wave passes from air into water, do you expect thntar+e)cwj *9 e frequency or wavelenanw j)+9c*tregth to change?

What evidence can you give that the s/rrsyrntf-+ tc zb(c:7 ml19 hpeed of sound in air does not depend significanf/sh nl 7tmcrrb9t+z :-c1 r(ytly on frequency?

The voice of a person who has inhaled helium sounds very high-pitched. w z2(,hxl kun20( y7cksw 9pcw(3b msrWhy?

How will the air temperature in a room aff uc5+ak m ,n.txgz7fd/ect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude of s ve k2v5c.o:*spd6 cabounds in various frequency ranges. (An example is a car muffl 6*c pov.s5d 2vce:bkaer.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as yomgp.-y-/dd/*opjn5 ; b vudy bu move up t5ybd;vpo/dgyn.pm *- bj-/ d uhe fingerboard toward the bridge?

A noisy truck approaches you from behind a building. Initially you hear it bu42sjbn5u f ssu3e u (pu8p74i7nkqjn*t cannot see it. When it emerges and you ds7q78snkb nup u u*sj4(2 ne35ipj4fuo 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 ig gj5u1qdcz fcn(tt09+g5u * “interference in space,” whereas beats can be said to be due to “interference in5ti 1t5g+uz cdc0f* j(uq9g gn time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the pointl7l i aq4tjx/)s D and C (where destructive and constructive interference occur) move farther apart or closer toget/j4l) alti 7xqher?

Traditional methods of protecting the hearing of people who worcy1w2 g0mr+jl k 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 +2 1cmlryjwg 0ambient 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. 12–31. Each wave can be th gkn 736ox+*zw cw:d(,sd hnauought 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 component frequencies farther aparn*s hk+,7w dz xugo6wn(c3:adt? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in the same directiod sz+*vto; gp4n, with the sop4vd*+ z ;tsgame velocity? Explain.

If a wind is blowing, will this alter tht9un,8c )k xa,7 oiycoe frequency of the sound heard by a person at rest with respect to tkot c,)a, uxn98c yo7ihe source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a va4 /nfnh h+6lchild 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 frvn/nf +h4l 6ahequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the e8zbak/oo 8*rc-b9vg i,o gg.hcho of her shout reflected by a cliff at the far end of the lake. She hears vk8ibg 8g/go.o o9c*az h,br-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. He hemdav4 6or+6fb ars the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume ther64o+ 6 fdmvab 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 wavelengtd+eodl5 2+d .iif0i gyhs in air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is drifting just ab4y3mjv 6ox 9nkove 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 (an3mox 46j9 yvk) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it ma;3ossp1y lk-c r f1sc*kes when striking the water belowp kf*3cos1r1s sl-;cy is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear (lw qp o3tsplo:1h7(jto the ground, sees a huge stone strike the concrete pavement. A momentp7lhl:w( s3j1( p oqto later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent erro:ephiek0r78i j r dz5tfz; q-6r made over one mile of distance by the “5-second rule” for estimating the distance from a lightnh r-p7z;itj5ze80:rd ek6fqi ing 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 dB?k hr : hm5h7xg bh2br2qo;-z5y    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level vp:(m:gepa1- x y hde*of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fireo0pw66bw(ien( go mx3ih e3(si* 6m btd simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint:bibw*to 3swhxm emg 0i( ( e6ipno3(66 Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four eb/ gwyco*gvao3)0 h4dqually 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 engine? [Hint: Add intensities, ogo0d 4wy3)ba hv/c*g not dB’s.]    dB

  A cassette player is s-gzzsejv/uy u6eze.6 s,f))uaid to have a signal-to-noise ratio of 58 dB, whereas for a CD player itz .u6ys),eufs/egzu)z j- 6ev is 95 dB. What is 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 om yp8wws2mx2 qpi7oz e++h:(pf sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads rough:72+ pm8wyxe2qw+ ipps mh(zoly 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 ear yp)ocy), hy4 ie.nlj)drum 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 icw*drt1 x1 g-es rated at 250 W, while the more modest amplifier B is rated a-e* d xcw1gr1tt 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 registered 130 dB when placed 2.8 m in wf 9/;4tiiced toq+d rfd-h-6front of a loudspeaker on the stageqt 4tde-;dw6dih+9fo -f i /cr.
(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.k2c7 hfi7f-ce 0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section i7fc c2 -k7hef11–9.]$\approx$   

  If the amplitude of a sound wave is tripled,zr6:t4muaif ) (a) by what factor will the intensity incret64uf)mrzai: ase? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have o rg9o9sfp)*cequal displacement amplitudes, but one has twice the frequency of the other. What is the ratio of th)p99*frc sg ooeir intensities?   

  What would be the sound level vcd j0xj,ad .gb (+*z7a6pxfs (in dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating aax.ags jd(v*cfd7p+,60jxb z ir molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tone th75 ixh:kau vb+h/:d ldat has a 50-dB soundhl7uvb5 d:i +/hakxd: level? (See Fig. 12–6.)    dB

What are the lowest a zvkbz t gcwx)i6 8;lv24:(urhnd highest frequencies that an ear can detect when the sound c;khv2zrb)i(vl6w8xuzt: 4 g level is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate agkjgjb8,vv s a2k6j(; huge range of sound levels. What is the ratio oj vk6,v8aj2g(k;s jbgf highest 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 hasr4k (4m/*c6d fgwfyrx a fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension mu(*ydrf 4f6xkw cgr4/m st the string be placed?    N

  An organ pipe is 112 cm long. What are thln+jq qw0z3. pe fundamental and first three audible ov3wz.q+j nl0qp ertones 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 frequency would you expect from blowing across the to9tz4m 49a psj)nnb 5exp of an empty soda bottle that is 18 cm deep, if you assum ennj5tbapx499 s4)zmed 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-tl fzwwl..m76tube pipes spanning the range of humanfl7 .ztww6ml. hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 54p:dnd()al 1uza t7hl00 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of itszd0ulpd 1(7:al) thna original length?   Hz

  An unfingered guitar string sa r q2pso5j+8)xvh3pk 7q9p3p gvlf) is 0.73 m long and is tuned to play E above middle C 9hqpp p37 o5v)+l3sspg)fvj2a qxr 8k(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 middle C (262ehb8v +ij1kt7bd2q e) Hz) whene7+1bidqhk ev82t b )j the temperature is 21 $^{\circ} $ C.    m
(b) What are the wavelength and frequency of the fundamental standing wave in the tube?    Hz    m
(c) What are $\lambda$ and $f$in the traveling sound wave produced in the outside air?    Hz    m

  An organ is in tune a(e/wxu n ;sd:-(cef xzt 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in cy(th ,0cx 1o)m plvd*Example 12–10 should the hole be that must be uncovered to play D above midd1 )chlmtdx,c p*v 0o(yle 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 resonaten u:g3,wqctn( at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequ: 3qwntn(cg,uencies in between. (a) Show why this is an open or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at both epq 0v0i)rj4+ed toxhiq +h5 (gnds. It resonates at two successive harmonics of frequencies 275 Hz a)vd54oj(hq + gri0pq xehit+0nd 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 xe d1+ p5eq6dz$^{\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 w0hb1*m0yfwey )xo(suithin the audible range for a 2.14-m-long organ pipe am xs eyfo0huw01(*) ybt 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 z3egy:tsw0w n6aabok383 ua:cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the aud 3nb: 8ag6ws3owu3 yaet0:kzaible range) of the standing waves in the ear canal. What is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to adjust 7cbz )+aa*platwo strings, one of which i)a7*+ clabap zs sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middl0p 4,ot c7chhyt*i0ufkww9p5 e 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 j 7e gs+:k7gthzdb: 98xaja3loperates at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are play97s x+ejahdt k:g3ag:j8 lz7 bed simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string prodyg0,vo ,si4 v 3wormg.uces 4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tun,,0vm4oo vsw rgi3gy.ing fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz.l6 djf9d7-6-dn)ytz ce try u36c:ges The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are playec7rln3c d- fjse-9tdeguz6y66td :)yd together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be by8)2jrdl/yl3 v b qg6r.3cup heard if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other at 25./rl 3l3gqv. u6rpj 2cy)d8byb0 $^{\circ} $ C?    beats/sec

  You have three tunincuo 3ejl685nph0tcv8ui (+w s g forks, A, B, and C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B 3sn8che0 u+5 lptu( i6vjcow8and 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 standsnb55 iwo,lwdgj./9u q 3.00 m from one speaker and 3.505/jnl wudq,9 wo5big. m from the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating at ( zrkzji ,(h.kpp+l1f 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the frequency of the other ?phzpi( .j ,kfzrk1 (+l   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 an/z gs;lv(3pn+w:rhr- gw hzv 8d 2.76 m in air. How many beats per second will bgrn z8-3p/;v rzlghw:s+hw( ve heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire enginefv w2kzk:ri140,j j ku’s siren is 1550 Hz when at rest. What fifkk 0rv,u z1 jwjk2:4requency 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. Whatarhiol (+ x*t+;pr 2wl frequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of2hroxpr++taw(i;l * l 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 tow zl1p*j +b8tzmard you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Arejp+lzm8bt z 1* 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 frequencywt9uqc *gzcd:xe) c50 horn. When one is at rest and the other is moving toward g*eqcc9 wduxc0z:t 5)the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receives the22tac/g8on7 sd h:ku sm returned from an object moving directly :2tgkuh7 sad2 cs/8o naway from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wagmhgdj:l)i h),- dz g)ll at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.ig) -lm ddhjg)z, :g)h0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was y1qs2;cds-f w 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 appr- c21ysds q;wfoached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeds. Supposex3soc( fs +x:jzbj84 j the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 mx:4objj3(x f cs+8 zsj/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 frequen ,rbbv7 m4pca6i69azz cy $2.25 \times10^{ 6}$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 is 1t)aq/:c17fpt 9 rfv qr2 m/s from the north, what frequency will observers hear who arqpt aq1/7 crvrf9f:t)e 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 i8v x12ghv4fni f 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 sq merld 2(u:w4ound is 310 m/s (a) What is the angle the shock wave make wmq(4r uedl2:s 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 so2 f/h/j*(awb x)cv 7h:ssqhzgund is only abhs2fs/ j cbvg (a*h)/7z:xqhwout 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s strikes the ocean. Determine the s 1h il5lp2n/l+k gqta-hock wave angle it produc5k lnl+l1g2-t/i qahpes
(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 q;vp7 mi8w8u( u .2 uwuje6rlg4, o,bmkbv:f a$/theta$ 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 thegu 1vj.a ,s,dc ground flying faster than the speed of sound. By the time you hear sadgu,, 1. jvcthe 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 wc 4r+86(s yn 6r,rejvp5kijrthat sends 20,000-Hz sound pulses downward from the6s,ke6rnrpwi5(j vr j +c8yr4 bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves areel .)jd7 jql3ohw (5esa1uv -s there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists vge:ru, cn: j)+tuo* .w-xgaspbrt0+of many plastic pipes of various lengths,pc wjeng +-t+sx: u0vo r,.)*a gbr:ut 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 soe; 1civau r7*kund close to the threshold of human hearing (0 dB). What will7vu *rc1;eia k be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-dB sound *cx f;sf,/t0adbj* nzare heard simultaneouslcf at dxf;z*bs0*j, /ny?    dB

  The sound level 12.0 m fra3u*dw2i.tf1s ze 8 tqom a loudspeaker, placed in the open, is 105 dB. What is the acoustic1st3 ite8q2zud *a.fw power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated a/aea q1mwckgac 9zo/wuc726 +6m pw x8t 150 W output at 1000 Hz. The power output drops by 10 dB2k+7 cmumw /aza 18c6wc 6pe9w/oqgxa at 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over their e4q c5t9*gts.aem *e wqars. Assume that the sound level of a jet airplane engine, at a 4egc w* 5q.* t9aqesmtdistance 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 systems, the+u hn- ycij-4c 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 fr9dpsp 2 d9qvsh9jvyvyu ;5 s9)equency 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 y /ovew9cf2p7l;x -d:zeed*6gppg f ;cm long between fixed points with a fundamental frequency of 440 Hz and a mass per unit length of c- xlpe 6ge:7*podd2z/fv;wf9p ;ye g$6.1 \times10^{-4 }$ 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 )4q gs;hr eg7l2g4mshys r,)g 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 levs2egs )44ggy r)l7hqg; rs,mhel 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 open at one ehky/qw gwgba 9a;2),f.u+gsjnd and also 75 cm long. How much tension should be in the string if it is to h g )g9wgkfq+uw,sj;aa yb2/.produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resona j 0 52k8jk3a5txwjrgxte as one full loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz range -7k4cf7lnki9qwpk z ( coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a clwkf4 (zpk79 ni7qk -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. Thepn(r+ h*c/a0k yw0oge conductor on the stationary train hears a 3.0-Hz beat frequencyc0epnwo* hkry+( / 0ag when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approachesrk (q 0n6(2kyks6obj f you is 538 Hz. After it pqs2j0b 66knkrkf(y o (asses you, its frequency 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 ca zccwuf99 mq.m y:ct:/,( a5s7w ehougrs just by listening to the difference in pitch of the engine noise between approaching and receding cars. Supp5/o9cqyuw 7cmt uwfm( ::h 9sge.,c zaose 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, produc6efv(*a slr)ee a beat frequency of 11 Hz. The shorter one is 2.40 m long. How long is the l6rs)e (a ef*vother?    m

Two loudspeakers are at opposite ends of a railroad car as it moves past a stk2+ qfb ehst50ationary 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 stf q bh+25ek0from 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 a aylh7ne+,l 1worta is normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz uln1al 7,yl w+ehtrasound 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 moth is flq0 yc/xgp/,6/gfo/ajggm:g d ying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of the wave detected by the bat after that wave reflects off the, 0q/g/ogy gdxm/ fgj/g6:pca moth?    kHz

  A bat emits a series of high frequency sound pulses as it approaches k-kfucp 7lhjl,vk*9k8+b b0 ia 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 bykvklpbc lkuk,h-+ 09bji f7* 8 the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was oncgyu cnu:c2b.l2i 6 tm5e used to send signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is aboyi2m:62u t5uc bl.n gcut 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 t/b z0z20,0 b65v f sdswwgxg6jjkp8vcompromised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. bw,z/ 0 sjtwjg2ksxp5 6f0 g6d8v z0bvConsider a living room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamental frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves 9 cik/pbo /h3nw42no8 wo-clya 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-cm-long ro/ hp43cyokw/9bn8-nw oc2oli d,
(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 hearinsu/ipk,bg 31tfbo/ 4 fg for the human ear at a frequency of about 1000 Hz iog fbi4bku ts//p, 31fs $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on the ground hears the zze/. *bh pwf)sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s altitpe zw h.*zb)f/ude?    $ \times10^{4 }$ m

  The wake of a speedboat nooc)i))im:ef/ 8ab cis 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