What is the evidence that sound tra3yc1p6g l h:kvvels as a wave?

What is the evidence that sound is a fi(f,ci t pw(sw9. xq2yorm of energy?

Children sometimes play with a homemade “telephone” by azwrf ( xuaw2.,ttaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sor(2u . ,zafwxwund wave travels from one cup to the other.

When a sound wave passes fru2oqky1o txu 3 qx )/;a3r;k yh/0uyhuom air into water, do you expect the frequency or wavelength to t1aok;yr o/x) 0u kyh u323qyuhq;u/xchange?

What evidence can you give that the speed of sound in air does not 9 l hgpedtx*8mo/ k/(9c ucqb4depend significantly onlcut9ke(o9db q cx 4h8m/*g p/ frequency?

The voice of a person who has 0nzlq gid)o0- inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch o2 g8ppds8+njb6 b ,grhqbm 1z1f organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude of soundk;d ug-gj*fqyh*upd x0t*e */s in various frequhtd- *y*qexf* /*g0uk;jdpguency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer t6vxcu9m noc7)ogether as you move up the fingerboard toward the bri 79cnumvxc) o6dge?

A noisy truck approaches you from behg9)wv qi-gbx )ind a building. Initially you hear it but cannot see 9)q )gg ixvbw-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 diffraction.]

Standing waves can be said to be due to “interference in space,” whereah+ on.fi*gu9sd*e dq.s beats can be saii n9ge+uqh .. od*dsf*d to be due to “interference in time.” Explain.

In Fig. 12–16, if the fdw 5 7fxrxsl+3requency of the speakers were lowered, would the points D and C (where destructive and constructive interference occur) move farther apa wd5 sx+lr37fxrt or closer together?

Traditional methods of p,pg)pl.6fqkb rotecting the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do notlqg)fb .pkp6 , 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 am:a xam1+vkf 9qyhj 4yei sofd;;4r39s a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two cyadf 41rxmh94 kjfe: ys+ 3;qmva o;9iomponent frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observerebykh3i*4-pvig kp ee+5gw jk7 nrt.g4+7ug+ move in the same direction, withe. *5gyk p4-k+47 +iptge niu3j7rh bgv+k egw the same velocity? Explain.

If a wind is blowing, will this alter thet nh:4e1rybuo(16rsz z;y7 f*weg:mm frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or ve4wyyme zb1u::n6t(gom1* 7fr rh s ;ezlocity changed?

Figure 12–32 shows various pokta7er ; bfp)t+ k8jbjsb/17t sitions 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, will the child hear the highest frequency for the sound tsb8k;kr+f1j e b )tbjp7/ ta7of the whistle? Explain your reasoning.

  A hiker determines the /k2n v.fdt-xwois 2u ,/xx5delength 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 2.0 s after shouting. Estimate the le t/ nx.oix/u-dk2 , efw2vs5dxngth of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waoa1o)rd pc)v3c sy)5 kterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not 3o )rpy5a )c v1ks)docvary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the waveleng bsix-y 1k7m wcqpe(4:u70ry xths in air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is drifting just above a sc.l ,nhfvp/1rkhool of tuna on a foggy day. Wit /hrvlk1fn.,phout warning, 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 clh a:p zjh:/-ppiff. The splash it makes when striking the water belopjh/z ap-::h pw is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike th5c1y1.u0o f+wilfx ts,dnk+ke 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 Tabluof0fk1. +kxtl cs1 dyi 5,n+we 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent errpl nmm:fcz1b0506usx or made over one mile of distance by the “5-second rule” for estimating the dfnmz5c6:0 0bl upxms1istance 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 paats)n cw24w oa9v) ,bbin 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 sq78x 6oqq zc 99rlxv/sze) r3tound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneously atkdk1w5a 5nhb 0 a certain p akw150hbdk n5lace, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplanmoavzr/3w 3p -40,s/ge h ghjye with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but onegw-/a0sp 3 hy e,h/gz3vjor4m engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to halfxmbz1u 2t:u4. wdf3ve a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is1lfdwz3b t4u:u.2x fm 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 sj ydy ;aq6 .bomx(e/)bta (e4person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly y.md e6qebyxo(ja4();/s b at 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 + -upnr4*zemwx2 mq8xan 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 251jx 3n*s w,s fswkqflo6:edfe+31vn ,0 W, while 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 loudspeaker connekfn*s fwl1 s,s: efd13oxjwv+63,qn ected 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 front of mq8was f63u5-hqg5 plvs(qq4 a louds(gv 8sq5mq435s q6ahu l-fw qppeaker on 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 detect a difference in sound level of 2.0 dB. What ienwq4 -v t.5vwsq:n(ns the ratio of the am.qtn s4-vw5w :(neqn vplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factosjtvp; vo h)83r will the intensity increase? Increase by a facthts o)j;83pvv or of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twice t2z 0ud +,wewx:lrrn*i he frequency of the oiur x0w2+ld,*we z:n rther. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in ai:5 *h/x(n jwtka anv.vr that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm a(j vatwh/ .v n*kn:a5xt 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz i+/qapj gh4;o tone that has a 50-dB sound level? 4ajhpgo ;/ q+i(See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear 9o )vqzhtf.5iuc fa;)can detect when the sound level is 30 dB? (See Fig. 12–6.).qtf; v5)fuha9izc)o

  Your auditory system can accommodate a huge rang7, 7r(bkfr ov xkd;ydbez9e5+e of sound levels. What is the ratio of highest to lowest intensitd dk;f79ek5y +r,7 borbvze( xy 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 l,nk paqas6j9, ength of the vibrating portion aj p,a96,qnks 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 lon6 j3i8w lmpk;ag. What are the fundamental and first three audible over 3 ;alikwj86mptones if the pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you ei/j xc:mvh)+uxpect from blowing across the top of an emh:/mjv c i)x+upty soda bottle that is 18 cm deep, if you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe ory0mv.59 wv;bhw i z1vjgan with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what woulhbvzim 0wv 1jwy9 ;v.5d 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 ahy t i2ww aiy4l*(29)wo8;fr*xyoqh as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60lw o w a9 *4q)y(*2fahyoi ;2twryx8ih% of its original length?   Hz

  An unfingered guitar/of6(w7 xael4 lt)sx j string is 0.73 m long and is tuned to play E above middle C (x ol7/slfx(j t4)w6 ae330 Hz).
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that emits mixggksl0pb*ir,. /f/ dddle C (262 Hz) when the temperature ip x/k if l0/srgd*,b.gs 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 20 y4e/poll3,f 8hkx zw) $^{\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 the hole be 2,d-aaim.dx sg /q ot:that must be uncovsi.a:q, d -d o2/gtmaxered 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 pi3za8.x i ae 8*f-;ajbi(j de.hxwsiv3pe can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or 38djfa.-ex bi*; zwhj.eiav3i( asx8 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. It resonates atjr i 6mghyhb)pau+/*4 two successive harmonics of fr/bm+4jhiha* ) p6y gruequencies 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 v)uhrazm83o 6$^{\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 2.14-m0g*auyyzj1+ u+buvjts7+7k a-long organ pipe azuaty+ j7j*ub+ v1yk s70uag+t 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. I (6sn ouq.2tt .sjm9yli tl4(xt 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 isy tuo 6qits 9mnj.4(l.(tl2 xn 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-1k*c pks zp b1+qgjj2 when trying to adjust two strings, one of which is sounding 440 Hz. How farcp 1kk2 qp1- j+gzjs*b off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (2mn ydj .4x,((h 7po;gwer6psyq,g6b n62 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 another4o* a2.t2g fz u;swhrq (brand X) operates at an unknown frequency. If neither whistles w;42 of.tqaug*rzh2 can 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/s when sounded x,b o:uy4dv5r with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Expb4xy r douv,:5lain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 o0elu,b0gra 0;4qkpw2 . wufnHz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings0e.ouun4;wb0fa,prk02q g wl are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutefhlrxc9arq0) 8 .p n0ks each try to play middle C (2628lx9rkfh0a n rqp.0 c) Hz), but one is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, Aee wib 47:mgqtw ;b;1aqkgr-0, B, and C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is hearq egt ; qa;4e-ki:b17bwrmwg0d. 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 wbm:4e:3)5eola lcdj person stands 3.00 m from one speaker and 3.50 m from the 3dloe4 eb)::jmc5 wlaother.
(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 bce2/ (7e+ tny(axusd a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibr2 u/t+(bdsye(e7 xan cating 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 map:eeh(g;j784jqq xbany beats per second will be heard? (Assume T = 20 jj;bq 8q4e :peh(7xga$^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz when c+eb *mx k*/fkqm*)zsq;1nm g at rest. What frequency do you detect if you move with a spekm;f)** xs/ c+mqqg 1kbz* nemed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you gut 2,g6+ivkbr-ub: gdetect if a fire engine whose siren 2ggtb+ ,6ug-ikr uv:bemits 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-Hz source is moving to;voq *9ofpb2jward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Arejf;9* pbo o2qv 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 frequency horn. When one is gp 3rq+c5l/w gnpmp()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 m5p rcpwgql+3n/(g)p Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sou23bprot(l p5 yrn0 k+xnd waves at 50.0 kHz and receives them returned from an opxr5 t( 3 on+2rlbpky0bject moving directly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall agyr urr)05 fv*t a speed of 5 m/s As it flies, the bat emits an ultrasonic )*g urv50frry sound wave with frequency 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 played on a movdtf; rcn) cs(2ing flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone w2s;fd (c)ctrnhile 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 use4ht v32kw)e nqblb/h.y1yx9z s ultrasound 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) .vxnky/yhtzb q3w9b 4el12h sound source?   Hz

  The Doppler effect using ultrasonic lyjzr0jxdr1 o0:p ;z/ 2lfr6 iwaves 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 frequency 570 Hz. When the wind velocna-8bvfcg.9yt 1 a:ry:co1lxity is 12 m/s from the north, what frequency will observers hear who are located, xlfc c1avtar-:8:. 1bo9nyg y 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 k+ma(s: ;9ptbskfn*bif 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 )(b)k.yhvrox is the angle the shock wa .xbrv(y)h)k ove makes with the direction of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmosphere of a planet whks 8c .5 rw6xsya*j6eqz xc5g*ere the speed of sound is only about*c w*ke xrsxq5c6gy. 5z86sja 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s st)p 3+.fegwmg frikes the ocean. Determine the shock wave angle it producefg + p)m3.gwefs
(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 (l1ufhi 7wdds77 ,ryx6 sp.)z mmhca )$/theta$ 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 exaccar.b-u;b xv 9tly 1.5 km above the ground flying faster than 9a. bc-v xurb;the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 12–34. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar deuvxkj 56fc1:a5 il/u4 p)rfla 5)elr hvice that sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. Ir /5fcal5j)1: p5h) uafiull v64rxekf 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 audible range)53l9 tec op44 mgsp//qfmnwp? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. Itva(ba2f nr; s83h zyc+ consists of many plastic pipes of various lengths, which are open on both ends. bay(sznvf ;ch+ 2ar38
(a) If the pipes have lengths of 3.0 m, 2.5 m, 2.0 m, 1.5 m and 1.0 m, what frequencies will be heard by a visitor’s ear placed near the ends of the pipes?
$f_{3.0}$ =    Hz
$f_{2.5}$ =    Hz
$f_{2.0}$ =    Hz
$f_{1.5}$ $\approx$    Hz (Round to the nearest integer)
$f_{1.0}$ $\approx$    Hz (Round to the nearest integer)
(b) Why does this display work better on a noisy day than on a quiet day?

  A single mosquito 5.0 m from a person makes a sound close to the threshold of0* (tutcstol. human h.t cuo 0tl*ts(earing (0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sounab4q 08cqv:bwx 7c * fq+ob(,c/bq.nptm8 jdc d level when an 82-dB sound and an 87-dB sound are heard simultan,q/ :bo0q tb4 ax+fqw.vn*mc pjq(87b8 dccc beously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open(lx8 ,*p) hobv /ybqnr7yy ,gy, is 105 dB. What is the acoustic power output (W) of the speaker, a,p, x* ygyh8o(qb7lbv/yr)ynssuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz5- .hi qmel /a4lmkx)x. The power output drops by 10 dB at 15 kHz. What is the power output in watts at) ma-q.hmx5 4liexlk/ 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over their ear1x hl +wbvarj1+jf gzo,( e7+vs. 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 hae +jjv1v (glz +fo+1,xwrb7h as an effective radius of 2.0 cm. What would be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communiioj vc7;k:*6qngms( ncations 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 tuned to a frequ6 to xt)q4 qtfnis.1kjf:9.hv ency 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 sz)k as +4nxa(d pqts7q p,01tqq ce,4a fundamental frequency of 440 Hz and a ,+, s0 qx1qt)(4se7ctapqpzaq 4nsk dmass 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 vibrati: xsx r6nj7p/x )/tbmgon above a vertical open tube filled with water (Fig. 12–35). The water level is allowed nrbtx gpmx6/7)/:sj xto 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 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar strinq/:uunv6x-qmbd0z6cj.*o: ov -kdm rg of mass 2.10 g is near a tube that is open at one end and also 75 cm long. How much tension should be in the string if it is to produce resonav-o:dqu6on-/0mc 6. jbkm xzd qv*:u rnce (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observe ng9wj: lsk1r2mtoy9f w9+p,zd to resonate as one full loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz range coming from two sources+in-ib hnayer;-36c d. The sound is loudesy6- b+c3;dnh-nra iie t at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a 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.yhj*++5jy 1pb d8g.ewuii3vf One train is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other i+ji3*y 8.yjv bfu+wph51e dg train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approaches you is 9u + g y+cf/elhu6q.w6a.pan z538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train movl+y6 g .e9un6 u/+ .cphaawfzqing (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars just b8yv3v4+ ue v *ao*5 4 xhyit0hbvvtwv(y listening to the difference in pitch of the engine noise*vvw(y+*ot4 a ev hv y8v3x5h0bvtiu4 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,6jx9i 7pcb1 ;fnuvl 7v produce a beat frequency of 11 Hz. The shorter one is 2.40 m long. How long is the othe9pvf7cn jvb6xiu7 1; lr?    m

Two loudspeakers are ah/la)xj64f ubkpb z93t opposite ends of 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 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 hb)kbl f6 hzpax4uj/39ave passed him, at C?

  If the velocity of blood flow in the aorta is normally about 0.32 m/s what6 efqcpw *as.9z,p ,vo beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? A fcvpo 6,qz,a9wps.*e ssume 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 whilb egxqfg;8 4-1b(eszen g+i,re 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 that wave reflects off thn1( , +efsqb4gez 8rig-bx g;ee moth?    kHz

  A bat emits a series of high frequency so +2gpya +vl--uv1u1narrvss)und pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can tv u gla2+psr- uv)+- s1a1vrynhe 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 sigctdiv l-0u: r:nals 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 3.4 m long, and it is called the F sharp (or G flat) horn. What iiuv-d: c0l rt:s the fundamental frequency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be compromised by the presenc33cvqsmx7n z.e of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a livi73s3xqn c.m zvng 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, cnfx mbp( )*ujpw9:e,lalled “singing rods,” involves 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 made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod*9u(x l,fje pm):pwn b,
(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 thrkk**h5tn 5gf terq 2z8eshold of hearing for the human ear at a frequency of about 1000 Hz it ekr*kzf552tg8 qnh *s $I_0$ = $1 \times10^{12 } W / m^2$ 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 Ma4 (sq26gy qh:wcwmj3ach 2.0. An observer on the ground hears the sonic boom 1.5 min after the plane passes directlm cwhg2 j3q:(64ayqswy overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat ;v p)v xlwk1c0desik )-e7w y: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