What is the evidence that sound travels as a sh, /wxb)+ xi78csy3 oxxa4i fwave?

What is the evidence that sound is a f(gc)s.t4few/uvfh1bv f k /4 form of energy?

Children sometimes plaw-.qlbnz 6dx20la b ) u*jwc1ty with 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). Exp )ld qzb2wwabt6uxnlc1*- . j0lain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you e+0y/fw :bzhty bg1k. ixpect the frequency or wavelength to chy .0w/1k+th bz:byifgange?

What evidence can yop.knx7wp9bx 7eb/u u*u give that the speed of sound in air does not depend significantly b bu n p7pxx*uw9k.7e/on frequency?

The voice of a person who has inhaled hel)f6ac;q 9dbap ium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of organ 4u*n1 3- oy tiipaf0fh sr6/bpqx-k2mpipes?

Explain how a tube might be used as ae ugyn.z x1bno4z 05p) filter to reduce the amplitude of sounds in variousb.0exo5 ug)p z14yzn n frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you move 2rvlz s +h r/uco.(pl :7mo0jlup the fingerboard tow72 h(zol:0u+ /rr coj.pslvl mard the bridge?

A noisy truck approaches you from behind a building. Initiw 4 ;gd9pb,rktk4 (lwhally 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-frequency noise. Explain. [Hint: See Section 11–15 on 4gtrb9lp wk4 (wk, ;hddiffraction.]

Standing waves can be said to be due to “interference in 6z05d7uo 3arlyfdi03c.onsovt v f :n t+rk8;space,” whereas beats can be said to be due to “interference in s3t i3d+7.6r:5dy0n8cnv0 ;kutooz l farf ovtime.” Explain.

In Fig. 12–16, if the fpevb53( pbxo4 requency of the speakers were lowered, would the points D and C (where destructive and constructive interference occur) move fareb (vp xp354obther apart or closer together?

Traditional methods of protecting the hearing of people whom x+;qne: l.gf work in areas with very high nois;.xeq m +fng:le 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 headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shownw,1 3s/wiu4tgx fv o-j in Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in -fwv,oxjsu4wgi /t13 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 and observer move in the hr/ )s/ hjr;+ .mocscx2e xbets1h, ux*e7ia. same direction, with the same velocity? Expxxh7ic tesec;hsbers /+j r21 o.mx,*h /.)aulain.

If a wind is blowing, will this alter thei xm nr1l8goui7.4mxj; +gyf8 frequency of the sound heard by a person at rest with respect to the source? I1;847i xgoy 8 m.li urxgn+fmjs the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A 36jw, difewm/ monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explaiw3wmf d ej/,6in your reasoning.

  A hiker determines the length of a lake by listening for the echo of her -fbrt.t,, m1nivcin:i2/rrnshout reflected by a c fv:t2bc,/1tr nm,iriinr -.nliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He hears the qvpjj7w w(5za t9/6kj echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary signiwkja( jv7 zjtw5q 69p/ficantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths i9mxxuz 0p(hm ++ is(hnn air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is drifting just above a school of tuna on a f thg6ecil ) xj09/p49yu w3xjyoggy day. Without wwyc/0lg)y6 jx9 9 tixjuep34 harning, 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 cliff. The splash it makes when strio,phgr6- 2o rcking the water below is , hoo6c2rrpg- heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the grou wlas-c9 2hzu5nd, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See w5 ahlzc-s 9u2Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by then;6ww9*l*5l0 )ibzkiy tu+kch7x gm t “5-second rule” for estimating the distance from a lightning strike i u* k il ilkn+9* wxhwzm7t6;c05y)btgf the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity o v34wf qvsr8t-f 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 sound whose intensity isuhj+wd9zq* vd.g :h3f $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound fe10ln8 u bvv9level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is l v8nfv9e1u0bexploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an/rd3dwlvh6r9ux y4 x0 airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 12r v9w h6duy04/xld3r x0 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas for w(oaej/s0 yzfms1j58oq:2 b+fe(ylx a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise fbooem y( q50xfa sfjw2y+e s(18 /:lzjor each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking i- r kl59qt)jpo0f pa4j+zm.ic:gs: jin normal conversation. Use Table 12–2. Assume the sound spreads roujfopj:+k5pq)g0:cs4 tz .irimj a -9 lghly 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 eardrum whose a;*ofdg*y k:h ksdscj 6a 7r8z/rea 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 n-)qf9yzw*v vtqw 4;wf *rq( z250 W, while the more modest amplifier B is raq;twq f- znv9*q(f y*vrww4z)ted at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registered 130 dB when placed 2.8 m in 49c)+/tltuo z fd8np nd 54osdyo4sq5front of a loudspeaker on the stagelfd)58 4oy+onu nso9 4tzqst54pc/dd .
(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 bqdu29z+gv:p18lxhwg7r. hd level of 2.0 dB. What is the ratio of the amplitudes of twod. 7zh:rb 28p9u1lg+h xdvgqw sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is teux4y.fo.rw2ef v1 tt5fa6b/blk*s) ripled, (a) by what factor will the intensity ivfu ef b4lew o 2y.*t)t1abf 5kx.r6/sncrease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equ* * k vld*+9u-ysplhakal displacement amplitudes, but one has twice the frequency of thev-9**ls+ uhay pk*kdl other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of ai11qhn4p7 yj a,+ ,wucehupo9 sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm aah yi9+q,7 po4jph1unew c1u,t 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tone 1etkec ge/7 h,that has a kc,7g1eh /ee t50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencie+3mkjk)u c/h qs that an ear can detect when the sound level is 30 dB? (See Fh/mkj+c u3)qkig. 12–6.)

  Your auditory system y6bc yl eh*()q viz-:vcan accommodate a huge range of sound levels. What is the ratio of highq6z bc yv ()*e-l:hivyest to lowest intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental bg;;m02:t*josq- i e1xgdi q dfrequency of 440 Hz. The length of the vibrating portionixsde 2tob0m*q:; i1-g; jdqg is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first three audiblimnh lb0osz5b.p5 tf)b)s/8 qe overtones if the 8b)l bbzss)ot mh . iq0f5p5n/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;hgf (8 rolw10tm ;kxahe top of an empty soda bottle that h;r0a(woxml t8fg; 1kis 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 with open-tube pipes spanning the range of hwcw;( o(.i rffuman hearing (20 Hz to 20 kHz), what would be the range of the lengths of pi( (ircf w;fw.opes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency o1e )o c;t unrq7 7ogf/k;agm:bf 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its originaakobtc;u 7; 1e )fm:g/g7rnoql length?   Hz

  An unfingered guitar string is 0 pzp0fj-h) 8gc.73 m long and is tuned to play E above middle C (330 Hz).-z p)fh8 gpjc0
(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 ansp*(7ze(lmy hf)my qm3 jdk(6 open organ pipe that emits middle C (262 Hz) when the temperatum7s6mjyq(f hd(3y(m le p) k*zre 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-m14i7cv qpa n2w a-oi 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the fn.qctq9n rr8 7ce/j, wlute in Example 12–10 should the hole be that must be uncovered to play D abqrtw/nr, n98 .ejcqc7 ove middle C at 294 Hz?    m

  (a) At T = 20 $^{\circ} $C how long must an open organ pipe be to have a fundamental frequency of 294 Hz?    m
(b) If this pipe is filled with helium, what is its fundamental frequency?   Hz

  A particular organ pipe can resonwibws. gz * fby*7j4la22hpq3ate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or a 2sby.4f*3z h*jibapq7g2 wwl closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.8ftvpo0 5: hocw q 4f-l2c/am:g0 m long is open at both ends. It resonates at two successive harmocm2 :o0f4:opt5 gaqlh-wv/f cnics of frequencies 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 4m m+iphx sduo4)t(zl41 uth:$^{\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 fwfm;11ixt)p6rfn xl ,ar:d(range for a 2.14-m-long organ pipe at 20)xlxf:a (1 r1rt,; nf6f mwpdi $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximatef,ji,: 4gik0 09c(qilww ttjdly 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 information in the graph of wfg,tq( lc w4jjk:di,9t 0 i0iFig. 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 twoy8a ,q0hqynd+ (v,wy nkex 02u f12zzy strings, one of which is soundz02ydk,8+hqn x2(fu,a zyy0 qw vy1neing 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if3wi +la*pem 9hy6xmn4 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 Xblrk15f1n5sd1a e hf 2) operates at an unknown frequency. If neither whistle canf15bdkr s2fa 51en lh1 be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/wq .oiuq )y w(l(wp(ouy4t8* ds when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. Wha4luwqo )q (yp8u((ywtd.*owit is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tunlwz/kx6o z+:m ed to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequenl/m:wzk x6 zo+cy heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play midd6.ofsz; l c pb62a5cippevhh qq3e775tez .x7le C (262 Hz), but one is at 5.0°Ceospla z3 ph66b57hi x75 ce.7c ze .;tqv2qpf and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B7j6fwo u fu,8m, and C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possiblowuj8f,m6u 7fe 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 speaker an2izbq.e2;a w.5 vbekh d 3.50 m from the hv5a2w.z;qb .2ik eb eother.
(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 piano tuner he )xz,fi2eb1v mars three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the frequency z)bm12f x vi,eof 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 2.6xwwic4 wmjx;2775 ker4 m and 2.76 m in air. How many beats per second will be heard? (Assumee w jxw5 xc47i;rwk72m T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency +inp9mwcw.v0 mn j*qp:z) ;kh of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you mq pc)vh.0pnijw 9*+ n m:;wmzkove 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 whos.vzj j4plaj*0te3 ,6bz sc5pk e siren emits at 1zzvpl ejak 0p6jjt ,43*c .sb5550 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 movio:,8fdr* ag+jlrh )lsng toward you at 15 m/s versus you moving toward it at 15 mh s,r+j l8ldg)o:a*rf/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 witha szec;7*a-ma the same single frequency horn. When one is at rest and the other is moving toward7-*e;aam szc a 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 kHzx ,88l1cgevc n4o 7o go5tgza6 and receives them returned from an object moving directly away from it at 25 m/s What is the received o n 6gv,g17lgc 4zea5oto8x8c sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As inxlihem 9ce301 cdzzxg9 z708t flies, the bat emits an ultrasonic sound wave with frequencedc3zn gezi07 c mx109lh 8xz9y 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was pr 7s9ub du. 9o6)kvghblayed on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone while at rest in the railway station. What beat frequency was heard if the train car approached the s799kohdsgu b r v)b.u6tation at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound 03 nxnm/vfp2b 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 2 cm/s directly away from the sound sour0nx3n pv2/bf mce?   Hz

  The Doppler effect using ultrasonic waves of frequency ixelbd .)axg 0m9hih2z ,9 jz.$2.25 \times10^{ 6}$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 14.k tyld(qpr:l - a //gt5ktde2 m/s from the north, what frequency will observr./d:etl4ygd 5t/k qp-t ( lkaers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if its hotcx0i9gdd2 -.5tdwficf)6speed 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 y3udj 9 ulk1(pdckik7i/4t9 t (a) What is the angle the shock wave makes with the direction oikl3j p9u/tuick4 71dd(ty 9kf 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 ie;pe-(1+ y * vvtvywdhs on+p;1y v*(ety-w edvhv ly about 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 mumq1uzhbk*21 x:f 5wz/s strikes the ocean. Determine the shock wave angle it produces *h1zu bwzx mf215uk:q
(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 8b6k+d.cqc:*np f hnpc. gsws+jp78q$/theta$ 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 abo.q-hoyan+o+*8 o jaitve the ground flying faster than the speed of sound. By the time you hear tho8+ h-in ayo q*a.to+je sonic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 12–34. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device that sends 20,000-Hz p(:(f koyzk6t sound pulses downward from the bottom of the boat, and then detects echoes.(kkf:6(t po yz 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 are there in the human audiblehu.pf.bpyosg m nk0 *(*) o:k tvsv5d8 range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewxq 2:ll(whvq, 7qcl3ser pipe symphony. It consists of many plastic pipes of various lengths, whichvlwq,l lhqs32q(xc 7: 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 souia)zhm580 au(, mmqr:n r9eg wnd close to the threshold of human hearing (ge:z(rr 950a,a)8wumqimh nm 0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound , yqc*6s b*4z.xlbrftuzxk0 -l)o:j blevel when an 82-dB sound and an 87-dB sound are heard simultanetl)40 x. : bfo,yljqk -r*scu*6bxbzzously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is gzj 2qz*ey16g ,q88xt7 kw-yxhuye:k 105 dB. What is 8gwtkxe*ez q,1ug:y8-q7yk2 jy z h6xthe acoustic power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at8g1 lhm7os*l( i nq9lm 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power output in watsn79hlg (ll*1m o iq8mts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over their ears. A(0 e21l.nd iwfs0j9wce2 cp fissume 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 dw2(f. p d fsw0lcin1 ecije209istance of 30 m from a jet airplane engine?    W

  In audio and communications systems, th8 e5- v1.lyxldb wbinkx4 v9y1e 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 frequenc(a:i q 6gmu2swy 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 lonfzljon;9v 0 -jg between fixed points with a fundamental frequency of 440 Hz an0-zf;on9 ljj vd a mass per unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration above a vertical open tube fil+e *q;b .jav(s0umxclled 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 tu*alb;q.se+v jcmu0 (xning 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 ai1zlmf9f ivckue -u)kn*j7 +5t one end and also 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 1z k)knivef i-+7c*lujuf59m tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one full lootih,;e52h4ulx v h-lcp ($\frac{1}{2}\lambda$) 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 x c3ojgp sc/1hb u b;yi4l7/:h500–1000-Hz range coming from two sources. The sound is loudest at points equidistant from the two sources. To determine exactly 3hpu/jbx7g;y c:i 1cho/bs 4lwhat the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. icj e2q(rs5 w:One train is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequency when thesc 5re wqij(2: other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train pvby m7*- 7r :3w2m(lvjok nxuwhistle as it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train mojl(:y7km7 r3umb2w vn*o vpx-ving (assume constant velocity)?    m/s

  At a race track, you can es8 e 66atcva2gtcg0oe6timate the speed of cars just by listening to the difference in 6g8 e0te62 oacvt6ac gpitch 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 straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency 5**acw2 z1iea7 p kikkof 11 Hz. The shorter one is 2.40 m long*e7zkwap1i ackk *i52. How long is the other?    m

Two loudspeakers are at opposite ends of a railrbq(07 w .uwp 8 2txrl3koci1lroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listens from the position A, in front of the car, (b) he is between tt3px8i(ouq.r1r bl2k0cl w7w he 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 abounb 8sp;5u o8ynt 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and r by;8n onsu85peflected 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 fle7t y3pkwh0+l ying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency o tywl+h7e3p0kf 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 approaches du3v. anatmtfw 41scn5, u6w 72dak 4qa moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be af4 d 1u,twk3 a7vq . 5nmnws26taudc4detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signals from 3xyehlvls* phko* -,0 one Alpine village to anoh*yk-3e ,sxo 0 llpv*hther. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G 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 comp tur2uea4 9kg:romised 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, 4.0uk49u:r2 eagt 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 “singingjvitm+ek5c,, rods,” involves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod ikc+,e5i ,vjmts stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the threshold of hearing for the human ear at a kq gcqtxsh5;4x* 7gxzrpb.28frequency of about qg 7cz5txsb 24x;hxqrk p8.g *1000 Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on the ground hears the sonic fk z hvx in-6jzj3g* 0+/v*ucgboom 1.5 min after the plane passes directly overhead. What is the plane’s alk g z*chzixj603v+j/vnu-gf *titude?    $ \times10^{4 }$ m

  The wake of a speedb3 b3)zewk9qlqto 0y f 7q,cnd*oat 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