What is the evidence that sound irfgf-);dbl2 ez i9 *stravels as a wave?

What is the evidence that sound is a form of energyun)n3a(dc)jws : ro) bst-tf(r6+nw i?

Children sometimes play with a homemade “telephone” by attach8ja,e0 maw .pring a string to the bottoms of two paper cups. When the string is stretched and a child spe a8w,0jp.er maaks 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, do you exphmbx4d.1a1hau n1lbf0: q3zlgpuh8/ ect the frequency or wavele z /hqdpblaa.01 h4uxb :g1u8l3h1mnfngth to change?

What evidence can you give that the speed of sound in air doe.j 8c ednqj;u7m2z,i vs not depend signifi78 .dj j,eqmic;v2 zuncantly on frequency?

The voice of a person who has inhaled helium soundsx2. f4nlf)veb 75 bvcv very high-pitched. Why?

How will the air temperature 31pw pixan2f x0 e8ff;in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude of sou97myo) 5fvzcv nds in varcmz 7v5 f9o)yvious frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer to b,u3d ;ghz/hdgether as you move up the fingerboard toward the bridg3d ;u/zhg,dbhe?

A noisy truck approaches you frjfy2 wn4wvi:ax5an iga2211 fjua8q 7om behind a building. 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-frequency noise. Explain. [Hint: See Section jfu75a 1a8q gyv1ij242:nw nia2xw fa11–15 on diffraction.]

Standing waves can be said to be due to “interference in smvfd8/go4 h x7q8k*gcgh 0r/upace,” whereas beats can be g4/uc0fmv 8d grh*8x o/kgqh7said to be due to “interference in time.” Explain.

In Fig. 12–16, if the fyn9y j03v i .cz;5mniqrequency of the speakers were lowered, would the points D and C (where destructive and constructive i;0 iczyinyj5 9.3mnvqnterference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who work x5hdqkue k.ne:a ):p 9in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sounk)dau:95.pe:q hnx k ed levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Eachp; ;5b niqn;im wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (bn;;i bp; 5qinm), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler swv jwq-ff6a5fz q .7v5hift if the source and observer move in the same direction, with the s-f5va vqzfq5 j7wf 6w.ame velocity? Explain.

If a wind is blowing, will this alter the q21af+x 8p lxfijy+ e2frequency of the sound heard by a person at rest with respect to the+yipeq+2xa21 flx fj8 source? Is the wavelength or velocity changed?

Figure 12–32 shows varioyv c (gubvx3/j/mj0p+: n i/ruus positions of a child in motion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, willm/x/j vb/ni c0:(3 u grvyp+ju the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines tyds( a) +ed9rnnj sg.2he length of a lake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo.n2ays(+) nergj dds9 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 hens2yk h3,3ohmars the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep ismy son,h3 k23h 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 wavelengtg: zx96(b1 z)xmx+wfjlswf .qhs 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 jushe8*whehn5 r .t above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boatw er*8h5.nehh 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 jz,l+v) az.x xwhen striking the water below is heard 3.5 s lat+jlv, x. azx)zer. How high is the cliff?    m

  A person, with his ear to thitx uxhp3ua))4lz/ a7e ground, 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/tza )3 pl 7)xuhai4xu s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent errorivgtuiui.q1.rk/8f1ctk)34vm ilx 5j fz-f7 made over one mile of distance by the “5-second rule” for estimaij7f851vc-lkqgz 4)urf f/ itim 3x. .ukitv1ting the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the p f g7m9lwa;cn2ain 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 ajd.t3v v;j+ zt sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB ehany3 ow px:r2v.ymic p;/8-when fired simultaneously at a certain place, what will be po2w v8yrna :p. ye x3ihc-/;mthe sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equal9nv(vsgql:eb yv 4nqh ,.iys1 v)b4w(ly 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 intensi9nvh.n)(v: s y,y 4qe1l (sgvw4vbbqities, not dB’s.]    dB

  A cassette player is said to ha,he.f9 ztl( yhve a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the 9zhe y,(h. tlfsignal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a pers:rk 1f+ ldxs*na8bh;won speaking in normal conversation. Use Ta 1h dx+ks 8awnr;*l:fbble 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 strikes an eardru):h4 hxyhd -hdfra0,ox a+u*i m 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, whi *.2gyy y(tghjle the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a louyty *.yh(2g gjdspeaker 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 metepku fp0-j 1+ytw2dx2q r registered 130 dB when placed 2.8 m in front of a loudspeaker t+fu p1- 2w2jxdyk0pqon the 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 de *hs3d:, bd)h7f 8g+ir- q hkrditdqe1tect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section qd ) dkrh8*dhrqds7f t -i:3+,ehg1i b11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (aheji 7f7rn 62ua.yul/qjf ,-c) by what factor will the intensity incre-f7yh6e liu cq /rj.2f 7jn,auase? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplit0d6cy h kvy.+iudes, but one has twice the frequency of the other. What is the ratio of their intensitieicydk0 y h+6.vs?   

  What would be the sound lev//3rpl +2w5ugkysmt z el (in dB) of a sound wave in air that corresponds to a displacement amplitudu/z 5g3+/ ykm2r wlstpe of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have whqm8s yo4 jqzs16e6iy8at sound level to seem as loud as a 100-Hz tone that has a 50-dB sound emoq6841 zsyysj68i qlevel? (See Fig. 12–6.)    dB

What are the lowest and highest frequencn1o)mqfud4 u q9ci+i9 ies that an ear can detect when the sound level is 30 dB? (Se 4d9)ncmq iuu9i1qf+oe Fig. 12–6.)

  Your auditory system can accxfz2.d4 cfv3c d9w3vx ommodate a huge range of sound levels. What is the ratio of highest to lw32fd. 9xfdxvz v 3c4cowest intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental frequency of 440 Hz. The llusf 1e e43voc17dosf)v8+ mnength of the vibrating portion is 32 cm, and it has eu7s8v meffo1 novc13 l)s4+da mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundafki:p+ n (vh6qmental and first three audible overton:6pi f+h v(knqes 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 frequ0u a z1lg;rci/d0h6jv 2c + lt.cosd4zency would you expect from blowing across the top of an empty soda bottle that is 18 cm deep+vaczlctj; d 4/61 o0h rzui 20l.sdgc, 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 hi ((ux zhi74pduman hearing (20 Hz to 20 kHz), what would uhxd(4iz7ip( be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmonic. +zrnp a7idsk 5f+7y)o What will be its fundamental frequenkn+s7a 7zi 5)p o+dryfcy if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0odww ny 1:;jedj4c 1 7fd(:va9wev zg5.73 m long and is tuned to play E above middle C (33wjdjcyz:ndwf1w( v;g d 4eva715:9 eo0 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 emit a:,y ;1(tjkxlq:gpxos middle C (262 Hz) when the temperature is 2qtl(y1ox::g x,jp;ak 1 $^{\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 v5x e 5vc7o-b.bpjtl : z8rw)oat 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 Example 12–10 should tf yfpg2p: +n)mhe hole be that must be :m2g p yp)fnf+uncovered to play D above middle C at 294 Hz?    m

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

  A particular organ pipe can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at a88o2m.4vbtukfll/+cls 3sb,x hr xb, nyo8 ubl f2vkbxrss. tl3,8lh c/,x+4m b other frequencies 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,tc1kdy2ev +u nkc8* p open at both ends. It resonates at two successive harmonics nv+ y8dk1kc*t ,e2cpuof 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 y.j8 4,ewom/vk). nwj we wl3r$^{\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 preseg7hymbr.h;9 cnt within the audible range for a 2.14-m-long organ pipe at 20hr mhg ;y79b.c $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is appro5idak+ada*nole gu9 c: 3.q3fximately 2.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate the frequenci9gc 3a:5qdla e*.kifoun 3+ ades (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 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 to8vmhzh)tc hh2 -.u (.0pxosg wo strings, one of which is sounding 440 Hm-( opst). hgzhvhxu2.c0oh 8 z. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if mijod6 bq;2p5tt/hqru o me3u/ :ddle 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 operatlcn * zk9*wft,es 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 simultaneo*ft *9 z,lnckwusly, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with ,r5hmlbo r- e7a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain yo7rhl,m -e rob5ur reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension in one:zp)os( h zgmuftr:+1 string is then decreased by 2.0%. What will be the beat frequency heard when the tw1rzsfut+:m oh( gp):zo strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutetw gya2;qg //ks each try to play middle C (262 Hz), but one is at 5.0°C and the other at 2wq; akty//gg25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B,h,f k,0c5 kjum and C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat f,cuk,0hkj f5 mrequency 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 possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A person stands 3.00 m from one spebc;ix+dis so.h*s :a w w:+h6raker and 3.50 m from t:h:oshir; +cw as6.ixsw+d*b he 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 ar iqbv)q5 e7b5de supposed to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibi bve 5b)q57dqrating 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 wavelgod sunxljwn.70j ag19 rd*1+ engths 2.64 m and 2.76 m in air. How many beats per second logj du*1n9rxsn0a+1d7. wjg will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s sii( ocvibv(dux9d,g n2k4 75pfren is 1550 Hz when at rest. What frequency do you detect if you move with a sf,4dogvicb d(5(2n i9k u7v pxpeed 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 fi(m*8jjp x9 yeore engine whose siren x(9jj* m pye8oemits at 1550 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-H4wom857gfvavj x kiw1wa() 7r z source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they close? ikvf5o a7mw(v 74w 1wxa)8gjr $f'_{source\,movine}$    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 /l0t4daq5sr39a9 kht4jfirq equipped with the same single frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assu3/ f0itlr4ha9dk4a 5qtrq sj 9me T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic so0nm-g7 7qhn32 gqb gr,fh3t jxund waves at 50.0 kHz and receives them returned from an object moving directly away from it n g 0f7,j7bhrmqgqtnhg -33x2at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall a*gvv-h)zz c - )jn(expt a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequ-zz-) cxe hg*vvj)p(nency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the originagl4y.,ov 5vo76 r-o9 opz yqdal Doppler experiments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a secoqoorgov d.95y ol76 p-va4,yznd 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 ulobveqbrhm)q h3- x+/zd 1ei :7trasound waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and th1o7v bmb i3 :qe-zerh/d+xhq)e 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 source?   Hz

  The Doppler effect using ultrasonic waves of frequencl3 8xe/n:jwdbn5g , 1f8nxg fky $2.25 \times10^{ 6}$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. Whenzub 1zhe ).k(br0km1n the wind velocity is 12 m/s from the north, what frequency will observers hear whm .0u(h1k bn1 kez)zbro 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 onh1zc:f. q7 ll//a0blx6qysvmm(5na q land if its speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where the speed of sound is 310 m/s (a) What /t cota1(i2szis the angle the shock wave makes with the dct s (/a12zitoirection 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 thioby;, +3touokh/wvcf1+;5mby dtt w- n atmosphere of a planet where the speed of sound is only about 3tdco ot/yw u- h tmvf1oy wbbk3+5+,;;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 shoyuchufzq 1vec8y )s u;2+6al/ck wave angle it produces 8u u )ql6 zac1 2+eh;/yvyfcus
(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 7 ml tg(jihn4 zh2s4j/$/theta$ 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 p-slo*;xp hw 11.5 km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled s;o* lw-1phpx 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 sound pulses downward fiy1,yfj u48f*j+x mugbx6r 5arom 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 tim+jy m ux,fgijf8r xyb1a4u*56e between pulses (in fresh water)?    s

  Approximately how many octaves ili2kn zjjb2w. kt3i 5*jm +y9tj/+f nare there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe sy* x4ruhobs. *lmphony. It consists of many4hsxbou .**lr plastic pipes of various lengths, which are open on both ends.
(a) If the pipes have lengths of 3.0 m, 2.5 m, 2.0 m, 1.5 m and 1.0 m, what frequencies will be heard by a visitor’s ear placed near the ends of the pipes?
$f_{3.0}$ =    Hz
$f_{2.5}$ =    Hz
$f_{2.0}$ =    Hz
$f_{1.5}$ $\approx$    Hz (Round to the nearest integer)
$f_{1.0}$ $\approx$    Hz (Round to the nearest integer)
(b) Why does this display work better on a noisy day than on a quiet day?

  A single mosquito 5.0 m from a person makew(mjce0e )( t0zm7a++xps tels a sound close to the threshold of human hearing (0 dB). What will be thxe 07el0s (mca)+e+tzp j( twme sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when d)qy +-foiiuk*h xk02e c9na7 an 82-dB sound and an 87-dB sound are heard simultc0qd-9nx + iu oyki2*ehkf)7aaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the o 69g7jhvj o4kte fco.5pen, is 105 dB. What is the acoustic power output (W) of the speaker, assuming it radifvh j4e67t.c9k o goj5ates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The power output drops; pemu3dnwm27gk1g u:k)4 cfz/ljog7 by 10 dB at 15 kHz. What is the power output in watts atg3:e7fk2dwm u/4 o mlp;)kcnzugjg71 15 kHz?    dB

  Workers around jet aircraft typicah:d lzi8j34z vlly wear protective devices over their ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the power intercepted by an unprotected ear at a dzzdv4 l:j8 h3iistance of 30 m from a jet airplane engine?    W

  In audio and communik .v :l- jqfum:pjonto7 (i(x1cations systems, the gain, $\beta$ in decibels is defined as
$\beta$ = 10log($\frac{P_{out}}{P_{in}}$)
where $P_{in}$ is the power input to the system and $P_{out}$ is the power output. A particular stereo amplifier puts out 100 W of power for an input of 1 mW. What is its gain in dB?   dB

  Each string on a violin is tun9cn v:ze7owt0 q1et)sed to a frequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long between fixed points with a f i*;9 pggptet+undamental frequency of 440 Ht*g tep 9pi;g+z 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 into vibratik87i/v )ihbyxon 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 fro hi7yi 8v/x)kbm 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.tl +kw+ 0 ,ar(-ebl0 2b,a2pltvqmyzf10 g is near a tube that is open at one end and also 75 ca+lm, (0fyle0t2a kbt vpqz-+rwl 2b,m long. How much tension should be in the string if it is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one full loo6 vn 92thy.o5sfn3 vwcknb1 4pp ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz range coming fuhqbhyca 2z4t *59,zhrom two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, u9,zb5cta2hy*4 qzhh 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. One train is stationary. The c y0qq b,7wwigxiv 2h:8onductor on the stationary train hears a 3.0-Hz beat frequency when t wh2qwy, 0v xi7i8bgq:he other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approaches you is 538 Hz. Afterlgx)2kzrpxdb- :s s2a:qf5i/ it passes you, iqx/s) l2 5:kg 2s-fad irx:bpzts 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 cars just by5fdg)8 +r.q1xvp.u v*f q bgsb listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the straightaway. How +qrf vb1x)bgfq u vgs..*p58dfast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frer4yx8 ( sro42n kzkmjb)-fio:g e0w6nquency of 11 Hz. The shorter one io0e b4w8gk) r64k -rfo yn(xiz:sn mj2s 2.40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of i8:0 hriraj,+:myvh i a railroad 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 i+ ia hrvr:8y,:mih0j frequency heard by the observer when (a) he listens from the position A, in front of the car, (b) he is between the speakers, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in the aorta ifd5* 7ahxc pi8 mgo:9gs normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow an9:i8cd*5hg pmxgaf7 od 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 whil/ qvt3*xv: fb5le+pt0 tslue2 e the moth is flying 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 tha +e0e bfv5tl3lv/t s2tup:x*q t wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound puwd6 , .;bubb6vzdo l/tlses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is ab/bztuv.b66l,w ddob ; out 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signals e oup;;,ns0 cm3safm1 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 i,mn1fup 3ase0scom; ;s 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 coeqr+ (:p.njk y,)y r .(pb.notn(jzg rmpromised by the presence of standing waves, whktn((rpz(rn:geo).q r +p.y j .j,ybnich can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamental frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involve r b q;dt.4y a(6vbziunh1.oo;s a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be madvq6 iz;h(o ;y 1 rdb.tnb.uao4e 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 ttm6g(* 3wjf0x rac.xrhe human ear at a frequency of about.wra x(6mfx3rgjc* 0 t 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 obser 6wzsdlgu(e61)rw zdr+ 1eyd)ver on the ground hears the sonic boom 1.5 min after the plane passes directly ovew)ry6 1zwrdl 6d+ 1 uegzed()srhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 15 a+l2 ojks2r/- f1273 rqql nqchmw ,2pyxm (nv$^{\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