What is the evidence that swz7ox2vs + tv*vh-+j um+loz4x 6pke,ound travels as a wave?

What is the evidence s6z hw4k+trmi i.s 3qlm0v*3othat sound is a form of energy?

Children sometimes play with a homemade nifl5hlq8deqzzsbj b x:n3z69/5 nd6 :42els“telephone” by attaching a string to the bottoms of two papq8hxl n:bj63n /dsbe:6zlfdz z49 ieln5q5 2ser cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, cu;x)7y i4 x9qyurl9edo you expect the frequency or wavelengt7)y c q;yrxu9xeliu94h to change?

What evidence can you give that the spe uz r95()kvouwr qh ,srs1)yg7ed of sound in air does not depend significantly on f ygh,k(uzv 5q wrur1o)9sr7)s requency?

The voice of a person who has inhaled helium sounds *5iv g5 rlsfl+very high-pitched. Why?

How will the air tempeqx3v w3wqn w0d-3by+ xcb2 8igrature in a room affect the pitch of organ pipes?

Explain how a tube might be usedp 5xhj7(ay 5ba as a filter to reduce the amplitude of sounds in various frequency ranges. (An examplej( b5 yxpaha57 is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you g4t ck4t60r xb)nx8kcv t;*cnmove up the fingerboard toward the brk xtgn cn6 4rt)k40vbtc8;c*xidge?

A noisy truck approaches you from behind a buil74+p1oou yx:h m s2dkfding. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-fr u fh4oydo+mx2k1p7 :sequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said toyph(wy kj+qp3e /ha;5 ct)qw/ be due to “interference in space,” whereas beats can be said to be due to “interference in; qhta+hk/e5) pwyqyc/ wj(3p time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the poe:s+8)jts1lu.h 8 bk lrh wpo5ints D and C (where destructive and constructive interference occur)18ls+l r5uo ekthpb )w8:h.sj move farther apart or closer together?

Traditional methods of protecting the hearing of people who work in areas witb(x )qs-px dwzxy3lf6nlu1;rfw3 :fr2x3q 3sh very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn3y:33 x( xlq2f)slf3xw6r pnu-1xfbqrs zwd; 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. 12–31. Each wave can be thought of as a supn4 bar q,udc++;2grm jerposition of two sound waves with slightly different frequencies, as in F,jg+m a; nr2cbu 4+rdqig. 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 and observer move in the same02q:d aic3vx.j 5bnvr70whcd am)k t( direction, v( hqdt03:cdiva0b)mnwr7x52ck ja. with the same velocity? Explain.

If a wind is blowing, will this alter the frequency of d*x33bz zsu2o3k 7jcp2dw k;ethe sound heard by a person at rest with respect to the source? Is the waveeokwj2c7b;us x dpd 3zk 2z*33length or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monitorjx zd60w:m0 zz is blowing a whistle in front of the child on the ground. At w 6 00mzzxjdw:zhich position, A through E, will the child 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 ec 6rw6nh3j0 ifwp1 7khwho of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shwijw66nh 7wkr30p1hfouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below th d3kl 2 fdf:mmymw*s/;e waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. Ho my:dl3 kmsf/;2m *wdfw 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 i jcz4u72yiek 6n 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 schoolwncfet,15s2+do, l gk 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 bac1w, tdf 5kle,+n2ogcskfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes wheh)6c8lr 2 e ygcv0l9wsn striking the water below is heard 3.5 s later. Howhe )8cy vcr2 slg9w0l6 high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the * bmd,x6guwuovo5 2 p*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 argo *x,wmovd6 u u52pb*e 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percen ,zrifv.rzfi41 z1j g1t error made over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if th41g izff.j,1i rvr1zze temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level cu4z)dx nj qrbn;3d.,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 whose int4;u zsxv/fqr3 fdvwpdu 0- q;0ensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when f-ndxrd8r0ip ;ired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hin; d-8rrd0i npxt: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equaj zdfu5)my (kkwj:a. 5lly 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, not dB’s.]djy()u z5kj5m k .a:wf    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB,bo- hu* ir re4-:b u//p1kotfs whereas for a CD playe-b u *1 /sfohu/:oebr4pt-ir kr it 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 of sound from a person speaking in normal vu/ fb2ri.;a pz5j(j 2 j,cwtxconversation. U2xuw.j jpci;(z bv ,jaf2tr5/se Table 12–2. Assume 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 s(n:xa(ws02s6p r7jv7il i 19ciinfo c trikes an eardrum whose area is $5 \times10^{ -5} m^2$ (a) How much energy is absorbed by the eardrum per second?    $ \times10^{-12}$W (b) At this rate, how long would it take your eardrum to receive a total energy of 1.0 J?   $ \times10^{ 3}$yr

  Expensive amplifier A is rated at 250 W, while the more m3ew5 8+ -kxue oh2ow+ ju1vdwkodest amplifier B is rated at 40 W. (a) Estimate the sound level in decibelsue25vex+ h k-dk3u+8j wwoo1w 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 rqla jsa60np 4+egistered 130 dB when placed 2.8 m in front of a loudspeaker on tha0+s6jnaql p4e stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound level of 2.0 df 8hnpr)76jng2p(opd np 3sg7B. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Secr 8 (nnsg6o3fp7j h)7p2p pdgntion 11–9.]$\approx$   

  If the amplitude of a sourp5 xls6 va(x.)uokg 1m5n9 *9mh nxafnd wave is tripled, (a) by what factor will the intensity increase? Increase by a factorh 9xaa l.65n5rmn(* mkvxo) g1f9upsx of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement+nu 1 z7tw) p0r1;9bpkzp zejq amplitudes, but one has twice the frequency of the other. What is the ra+;zupbp1eq71 tr w jznk9)pz0tio of their intensities?   

  What would be the sound level (in dB) of a soqrwcg/.30 )p hxsso)uund wave in air that corresponds to a displacement amplitude of vibrating air hwq3xug.) s)/0s pcromolecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have whq9yg 2f p k;kne 20yszh,dpq,(at sound level to seem as loud as a 100-Hz tone that has a 50g(k2;yepd2p ,sf qq y,h9zkn0-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect izidzr471:cw/zy d6wqo(h/r 0 dfb1f when the sound level is 30 dB? (See Fig. ydwf4z i7 f zo(c/bd qr:/1rz1i6d0wh12–6.)

  Your auditory system can accommodate a hu)yz*-,s( v2ok wlur48 hhwgfk ge range of sound levels. What is the ratio of highest to lowest intenrw),zf hk(-s g4w*8vhk2uol y sity 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 tdf:+88xepf j 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 must the string be pla8fdxt8+p fe :jced?    N

  An organ pipe is 112 cm long. What are the fundamental and first three audible o-rqrt/o4 dqv ofz*a8(vertones irf rq4/t(aq- zvod 8*of 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 t.ukw xj cl2,ulfc *(k8he top of an empty soda bottle that is 18 cm deep, if you assume(c*fxu, w .l8ul c2kjkd 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 pipes spanning th p m:+hjoj)earq61s3 k7iwt k+e range of human hearing (20 Hz to 20 kHz), what wourmk:6 pjsj+ 7 1i3 )qkaho+wteld be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string har4 :fkpx+om*5x li7-1i ghen rs 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 original lengtolp* mki47 e 1f:-x+n xhgirr5h?   Hz

  An unfingered guitar string is 0.73 m long h kdk1dv0d- 8s zml41oand is tuned to play E above middle C (3301d-ksd k0 m 4dolzhv81 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 x79 tsmvh.bla olj; bf:3ljt,1; z l-semits middle C (262 Hz) when the temperatl7 jm fbsah :zt.,xv;lts jl1o -;lb93ure 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 2wtw/2udzz e(-i 2q ,zl0 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Examplv 5q2b29xa6 b odi9,3zlakmcg;0hk t we 12–10 should the hole be that must be uncovered to play D above midz2 i2av bmdb cgh a5k q;x06okt3,9w9ldle 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 resonate +p/;vfwn1r mu k1e+roat 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a)+m ;ve1ok rr+/p fw1nu 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 ends.srsssft ,z1/. It resonates at two successive harmonics of frequencie,s s.1stsz/ rfs 275 Hz and 330 Hz. What is
(a) the fundamental frequency,    Hz
(b) the speed of sound in the gas in the tube?$\approx$    $ \times10^{2 }$ m/s

  A pipe in air at 20 mq*80hwsgpa8 xq. lein;p5 * e$^{\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 the audible range for a 2. muev n71g e1/;fk9 g8opee/0ds+xfaz 14-m-long organ p m pvk/s/09xge de1;+ee oaf1 gzf8u7nipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open t*w/tbsi (c.rihw3iu 9o 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 relationw.i/*w(r3ist9b ic huship 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 everyg3.z t/vx7v;oyb9pdh 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far of; 79gozxybv/ d3 ph.vtf in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hfq:mv9j 0g8 8sdh5 8lkd1w oa(c; zxbjz) 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 operateswob v4yxldn2v- 7gndhh vx;4l+2,q t+ at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played s7 v,;bw h- ho+qn2n42 xdl4gv+lxvtdyimultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tunind 9dnk pk stpu64u.(0lg fork and 9 beats/s when sounded withplu (k6d u49k.0tdns p a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tunedbtu;w3+ozi6 idqabcv cw/48 gb9;,h l to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be thi8lv 39b;ag;d6bcqc z,wwih t /b4+oue beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two idyvj h ybbth ek6,w;b);qnq38+entical flutes each try to play middle C (262 Hz8b;vhbkq6 h 3nyq)y twe,jb +;), but one is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has aaxhk - 8m/c3hr 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 beat frequerh-k 8 3mch/xancies 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 1.800(*w u ydgqfzy-y(f l( m apart. A person stands 3.00 m from one speaker and 3.50 m frow*fuq lyfy0(zd((-ygm 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 132 Hz, but a pian. a5*9c4 ba.m mb1ulz3fnrfxuo tuner hears three beats every 2.0 s when they are played together. (a) If one ax3.49 nbz5bfmcm1afu u*l .ris 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 2.76 m in air. How many bem s zoh84wotx.4n;yd2 .jf8hhats perzsh o.4 f. yt8mx n;4w2hdhoj8 second will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of okd(e9tfubx;vr9 ppox9+0deg*3 j 1sa certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speexvje*p 1gd9tf3od9 ;x(s bp0r u +ke9od 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 sypp9)wutn(o ejo2- 7m iren emits at 1550 Hz moves at a speee2jt)m ypn(u7woo -9pd of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency isdmhb*6b- o5 2q mq,jef a 2000-Hz source is moving toward you at 15 meq h b-q*bd,265omjsm/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they close? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with the same single frequp4sdxzapx. 9*0we7ok0p vhx9ency horn. When one is at rest and the other is moving toward the first at 15 m/s xx9 ps. 4*zkav p7h0xew0o9pdthe 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 ultrasonis:rau0 dm:*7/r opdjfc sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is 7 :uarrd/sod pmj0*f:the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s A 4nb,jrsri80ts it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency nr08tsj4r ,ib does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments,x 0+gt 39fchm8pjlqe8 a tuba was played on a moving flat trainlthp9exmfjcq0 3+ g 88 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 speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measu8 :waa/yyr zp/re blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sounda/ay8:/rp wy z in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultl*x -0v4urzxbv u)ao/ rasonic waves of frequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of fxnd8gk. m.( a aw:sy *e4awd0nrequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are located, at rest,w:yead k* g4.a 0nm.xwd8na(s
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if it53mpjy ce, kg6 9t-r8zpy1,wd.xg izms 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 sound is 310 m/s (a) What (kcymgsr0w*y7z 6l m,is the angle the shock wave makes with the direction of the airplanemrwmc*ls (zg 6y7k, y0’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 t- a. cj29/wujzk.bx zqhe thin atmosphere of a planet where the speed of sound is only about 3-z ux c /2zaj.9kbqjw.5 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 shocmm 4j p. hb))kpmpd ) 0laz-rl nq+29bsziqi66k wave angle it produ)pqh+r 64ik)ps6 lza-9bmpql2i)m.z0 b djnmces
(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 1n0df:b-y zc j it*vz1$/theta$ 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 a3v afcmxt8ztv),,c1 .5 km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 138 fa1,,z tcv)ax cmtv2–34. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device that sends 20,000-Hz sound pulses downwardgi5qxt.2t)()mk v8lo xllik7 from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 200 m, what is the minimum time between pulses (in figqoi7(8xll5m )tv2x.k) l tkresh water)?    s

  Approximately how many octaves ax4 -1vgpn ryz9hlr 9bui:u1/j re there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a displ: z9gu.g, gf:1fbsumm 6 5qoqtay called a sewer pipe symphony. It consists of many plastic pipes of various lengths, which a1 qg:guq 6f tu9zmgmbo,f.5:sre 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 souoc xn tlv1mfk3.af)// nd close to the threshold of human hearing (0 dB). What will be the sound level of 1000 such mox/1 ntlv k/c)o.mf3fasquitoes?    dB

  What is the resultant sound level when2 5 oun-iduj,rgiyt3xywlrj(3mw1 ,) an 82-dB sound and an 87-dB sound are heard si53 rjl(wy)u j rxtni-dmgw,,iuy 21 o3multaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 dB. Whatoo03b) vemfx jqxqpp/:w2.3 j is the acoustic power output (W) of the speaker, assuming it radiates equally in all dirjow2 3fpqv).: /m3e j0oxqxpbections?    W

  A stereo amplifier is rated ab9gw 5iy/uapjh6t* tyyhh z2;pp( w /d3l t;r8t 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power output in watts at 1r;;d/zy*6hi wt2a3h p yp/9gluh b(pw5y 8ttj5 kHz?    dB

  Workers around jet aircraft typically wear protg eo;k,la0og)xuke;9ective 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 a distance of 30 m fromkg 0)o9lugeoka;,; e x a jet airplane engine?    W

  In audio and communications systems, the gaihto.- gr s9d+rn, $\beta$ 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 frequenu kx0x--0 o mdsr2l;umcy 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*cc,rjq mh cm;vpmek7*/d 04 sfee.,h is 32 cm long between fixed points with a fundamental frequency of7s. ceq,ef/k; hd0epm cm4*vh*mrc , j 440 Hz and a mass per unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set intoiu1fczj*g2 ilo pm*f-o ux 4:e,ci4 y2 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 air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.3* ciu,l:e p2ijc24ozmy uf1-i x*4ogf95 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 end4n/wgs- czkk(e n8d:c and also 75 cm long. How much tension should be in the string if it is to produce resonance (in its fundamental 8ezk 4cs/ d:gc-(k nwnmode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to rx,sd,c b0oc0 o /m fg0u0,cbbjesonate 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 500–10xr-iq;jkl -v)g8 ykd.00-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 about and finds that the sound level isr kiqxvljy-;kg8 d) -. minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The conwiqamo6-l;lwul0 f/ xitz ka,p826i;ductor on the stationary train hears a 3.0-Hz beat frequency when the othepl8ofi6;xu, lmawi i-kw t lz;aq2/60r train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle kd5hpx7,sd )sas it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was theshxd7p5,s)d k train moving (assume constant velocity)?    m/s

  At a race track, you can estimate tkqie* ) vu/tf /r0g*/egx8hhdhe speed of cars just by listening to the difference in pitch of the engine noise between ag/f *0qtu8hr)idk*e xevg/ /hpproaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat fr+5lmjl: s yzlsv,7b4e equency of 11 Hz. The shorter one is 2.40 m lm7 ,b:jl5+ssel 4ylvz ong. How long is the other?    m

Two loudspeakers are at opposite ends of a r+rc3m8 rzme/b ailroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listens from thz8m /mrrb3c +ee 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 tte6x-( ;hlgevw 6 l67e:smqw0.32 m/s what beat frequency would you expect if 5.50-MHz ultra6:et g7 h6tm ee6s;l(qlwvx-w sound 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 flying toward tcfj2-lzqb9 o; he bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What izfqo;-9l jcb2 s 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 sound pulses as it apphdobz ;msk1c-4lp8 3q roaches 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 returns before the next chirp is emi8 c ;zl4 khdm1qpb-o3stted?    m

The “alpenhorn” (Fig. 12–38) was once used to senuxbi+f ho-x )dp;rg73d 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 about +od- rbx37ip;ux )g fh3.4 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 :3 py .s-y;bg0ia nryulistening 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, 4.0y;y3gpin s0:r-.yua b 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 a long, slender aqd p6*2-in f.lkk xvps* h5ev-luminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rpknlexs56-k2 id*v*-pfqv. hod can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the thresholda ky,uw ks3a+* of hearing for the human ear at a frequency of abo3wau*k+ k,ay sut 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 )ai+hievfeg f 93 b7sj ;kq:w;Mach 2.0. An observer on the ground hears the sonic boom 1.5 min after the plane passes directly overhead. Wh3fi;gwk7 ahq:bv +s9; fe) ijeat is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedbo*u15wj u jxc * nhw/hbhka au64*6,vgbat 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