What is the evidence that soug5*cd o/ ok+d qe/a2 8yb;cenynd travels as a wave?

What is the evidence that ulk 34wbo1g o*vd5r5asound is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a str mud0o s2/p*qq6 slzf.ing to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the soupsmsl2.dzq*0 f6 ouq/ nd 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 a wet6 b byx9b:+wq*3jkn8gv*fir into water, do you expect the frequency or wavelength to+ nywwv:g jxb*9t6q b*e8f3kb change?

What evidence can you give that the speed ye+8c;vg ql xb7+9cwpof sound in air does not depend significantly on freqb +w+yvqe;87 pgcx9lc uency?

The voice of a person who has inhaled helium sounds very high-pitched. Whsdzbx9.;kz*r2(jfq s y?

How will the air temperature in a room affect thqf3h70ze fk 1je pitch of organ pipes?

Explain how a tube might y .fj;2unza s(:zv) fvbe used as a filter to reduce the amplitude of sounds in various frequency ranges. zsv v;u (fj)2:.ayfn z(An example is a car muffler.)

Why are the frets on a guitar (Fig. a lvmxe,l- ;t7qx+1 xxuvbn8-12–30) spaced closer together as you move up the fingerboard toward the bridgq1m;-x,ux av-x lt+8b 7xnleve?

A noisy truck approaches you from behind a bwq xb guhe);1d,c1l7suilding. 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 teh x bcw, 1l)u7;gsqd1he high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference inliqi /j in:.qa hn: 7)ykvq;d) space,” whereas beats can be said to be due to “interferen /a;in.::dvh k7)qinqi q )yljce in time.” Explain.

In Fig. 12–16, if the fr jurk* tk-vj78equency of the speakers were lowered, would the points D and C (where destructive and constructive interfereu78k*krt j- jvnce occur) move farther apart or closer together?

Traditional methods of protecting the j, eri*-mhst 9hearing of people who work in areas with very high noise levels have consisted mainimrs,t*9hj- ely 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 shown in Fig. 12–31. Each wave can be thought of as a h*l )nxf,bneyhyrgr-31n8,t:0om brsuperposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), ar3fyhbe yn *bn) tl,ghr m n,o08x-r:1re the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in tabw*z64x,b9ae5 cs ; /vf bzkihe same direction, with the same 45v9 aw;bzxe fb bizs6*a/c,kvelocity? Explain.

If a wind is blowing, wilk+uxt3w.h c j8l this alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocity 3j .8wcxt+huk changed?

Figure 12–32 shows various positions of a child in f lv4/kg( w(mkmotion 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 of the whistllfvw( 4(gkkm/e? Explain your reasoning.

  A hiker determines the length of a la((amv:r:c * zdsuoutpn4w)3 vke by listening for the echo of her shout reflected by a cliff at the far:c:aduz34o m sp(vnrv*w(u) t 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 sy(6dvd7zjg )4-xu7pu8 dwg s. He hears the echo o77d)6v j-y z4sdpxuwg g du8s(f 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 significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in ai i7p4-dmaq b(gqf f/a0r 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.vle2m8 jxlt00;vmhqw d03wa drifting just above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another ev ax02;hm0wlv3j.mwt l0d8q 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 ofd88ewejv*,j0pdtsu 2i) v/wc a cliff. The splash it makes when striking the water below is heard 3.5 s later. How high is w88)ud/ipjtv,2e dcj vs*ew0 the cliff?    m

  A person, with his ear to the gr6 ,3sqa.rwqb;+ku o k0yveg.8bsc1zsound, sees a huge stone strike the concrete pavemen8u;sc1,ve.ar3.kygq06wq s+kb o bs zt. 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 Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made ofhb;n8j2 ;u vover one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (a)h ;8n;2v buojf 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pai:qoyudo*. ot:a8tr8 tn 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 intens xz41,9 :-zbzgzefn wczi8xiv+ bfr0)ity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simu;h 8v-6n3 zjyjk 2hovsltaneously at a certain place, what will be the sound level if only one is exploded? njz2k -6h;3vvyosj8h[Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equallya98ev.gi2kp 6wvj7xv d..73(nlott bq t-vls noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if t7g t3v-l vx(wl ea.sbpq9t..o k8n26tv jv d7ihe 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 u *o5jkb,mgs .a CD player it is 95 dB. What is the ratio of intensities of the signag kj5b mo.s*u,l and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound b8lc(6d9-ou v ,n nxaxfrom a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphedoxnn9buv l- c 6,(ax8re 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 m(0i0ussy-c can 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 2)igm4jo4lp2 adqp ,4.:ro elz50 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the soundz,goeqplo42 j4p a) i:m l.d4r 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 registerecu0pe3 g- cc7kd 130 dB when placed 2.8 m in front of a l-upcgk3c0e 7c oudspeaker 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 dik( c:vyfge)36ys qn3nfference 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 n33)ky:6 ygevfqnsc( Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripledgpc,bqc ; r81dml.tavc :2l4x , (a) by what factor will the intensity increase? Incr d2x, 8tqbc1glcp;4al. cv rm:ease by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement am/pw 1 *9slv7)t smoicg2x5awxplitudes, but one has twice the frequency2ot7pxvg*a m1/ 5xswiws9)l c of the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that corresponds kr) a0d+c6 vflto a displacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz? k)+lfac06vdr    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tone that aav c5l oe 8 ipztup 2v;io/79-;yjm5khas a 50-dB soecva/7m ii-9; ;5a5pozklujo2 vy8t p und level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencij; f h, pvkv9xq8j2,vges that an ear can detect when the sound level is 30 dB? (See Fig. x;p vqv,g2v98,j hf jk12–6.)

  Your auditory system can accommodate a huge range of sound levels5q-g is4ds/mb2 at 4wo. What is the ratio of highest to lowest int52bd4q wo4-t mi/sgsaensity 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 length oflw sv* ikr cvuraz4mr- u5*3gz)2f 1n) the vibrating portion is 32 cm, and it has a massl4scr-w)n u1av zz5fruig )* r2v3k*m of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are thpj9;l0:9wkrel 5c y7v fk pxz8e fundamental and first three audible overt8zxwp59l:cfje;r vk 07 l pyk9ones 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 ivd l. s3.h7vka:i n:iyou expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tubekins. hvav: i3.7l:d i?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with yoc * b62zaa/oopen-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of thcza b*/oayo6 2e 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 tf.:qtcc 9m p.8lueh9k 0mh:w ohird harmonic. What will be its fundamental frequency if it is fineq.9 8mfl0wt9kpumc.o:hh: cgered at a length of only 60% of its original length?   Hz

  An unfingered guitar s(hl:w6:prc.uk x1 v uitring is 0.73 m long and is tuned to play E above middle C (330 Hz)c:r (:ipu1 wkuxl6v.h .
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that emits middle C (262 Hz)0,da 0.36qed ggfz2 .cvp oqqlsg2x+u when the temperature is 2sx.dq g+gc0.0f22vgeu6 dql3 pozqa, 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 at 20 2n)x,ap6:dv6p8z tq hyrg 3zbo(y0li $^{\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 pyi8 p u65u losp3oq5fmctr-6q2:oc312–10 should the hole be that must be uncovered to play D above midtc6cu5 8m5pqo32up-q6oypi :ofr3sldle 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, and6zf o7jl :ew7i 616 Hz, but not at any other frequencies in betwe6z: ief 7jw7olen. (a) Show why this is an open or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at both r 2yhm. 2ul/ghb82hwk ends. It resonates at two successive harmonics of frequencies 22/2b whgh.yrmk2 l 8uh75 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 +o qgve7 i0t3 8+ikaql. zkp.y$^{\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-m-lob:z: mqr6r)hf*/eb kang organ pipe at 20 bma6fz:r k q:r )*beh/$^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open to the out*ig2veok+d (jyzdv (.side and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves i e2v+vik(dg j*dz(.yon 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 two strings, ,d46qq nnt. o3.dbs xbone ot dx.qb6bs q.nn,o34 df which is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262*wch ;9o 7:gvleynie-e+n+in 8dbdt + 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 (/l- tp2lnbt cx7th0n ,brand X) operates at an unknown frequency. If neither whistle can be heard btb2pl0 -hnt7c,xl/nty 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 with a 350j fg8;qabk.,c )ic5 ci-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork ;i )ic gqck.8a,bfc5j. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tens 8b+ ebtkqcp6 3lm(pei8(kh)n ion in one string is then decreased by 2.08n()btm 8k eqi pe(lb6+c3h pk%. What will be the beat frequency 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 d06cabyx9y4g w 26z.bp 5dwp8w fw5g aplay middle C (262 Hzydcbga80dp5pw. y6f w9wzwagbx2546), but one is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 6++yk+ vphd9ox .ghqjco(e 04bzq6hw 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. Whath +k6vpqod hy.wq 4xcj9o6b +0eh( z+g 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 spea: x d+jod/ow4sker and 3.50 m frj 4 xddo:/so+wom the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating a 8sn1u-zj;u vi-a1;cj,lcwrw xq(9 zft 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132zj r s ;i,zf-vu ;j1x(cnwcwl9a q8u1- 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 w n+w5wixn,u c, n(d5rpavelengths 2.64 m and 2.76 m in air. How many beats per second will be heard? (Assumiwwdpn nr ,55n,+xcu (e T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant freque7gu ks7df7n89gmuqn5b5se o :ncy of a certain fire engine’s siren is 1550 Hz when at rest. What freskngs78buf eo m95 q:7 d5nu7gquency do you detect if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a fire engine whosejm 9( /so 5,/ufkmbkpr siren eopj //srmb ,kmuf9 (k5mits 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 f)rv1m9y* i liyrequency if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s lr iiy )y*9vm1Are the two frequencies exactly the same? Are they close? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with the samhh* 7 tz.(h )j8;l/ld9bb 6yekth sdgze 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 em9lylhb87k6 z*/dedzghhsthb.( ; j) t it? Assume T = 20 $^{\circ} $C    Hz

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  A bat flies toward a wall at a speed of 5 m/s As it flies, the bn 0l vc1 b9xn8ektmq:9at emits an ultrasonic sound wave with frequency 30.0 kHz. What frequencn n9c:em08tlkv1 x q9by does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a b;4qi( emy 9mutuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a speed of 19qi m;uemb( 4y0 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves tov+ay 49b+a :k fuxss+o 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 + xu4a +9saofy:+svbkthe 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 ulq6 d+sh11 aksetrasonic waves of frequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequency 57x7-f/x kdkqk 50 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are located, at rest,x5k-kk f7dq x/
(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 lhdx8flp2 p-j2and 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 whe0fy1 qj6ryn5 q5qz, tlre the speed of sound is 310 m/s (a) What is the angle the shock wave ma6qyl5y fqz5qt 1 0j,nrkes 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 qyba-goswnpyt-au 6. 4 .g6+ja planet where the speed of sound is only about 35 tu+- awg.. 4 y6asyop6n-gbjqm/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. Determ37gnxj. v;o zmyqy8)kine the shock wave angle iyy x.nzq)m8ko; 3 gv7jt produces
(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 ;:p- s xux- 18nkkvt*vjymrq4u +5huc$/theta$ 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 1.5g4z9omci+ m4 d km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal distan49 4zi+mgdmocce 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 pstsf -5478xfvfhvm +pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designevpt sx+m487sfv5h -ffd to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many oywy)o t3hfzj4nznf.i82e , )+uxwxw /ctaves are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphon 3cl2;zm xq:(imnn r(.hi:semy. It consists of many plastic ph;qz(( rmme.3 :xcms2n:li inipes 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 makes a sound close to the tr;ge/ p,vf;vf hreshold of human hearing (0 dB). What will be the sound level vfrv,ge/; fp; of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-dB sound are heai:np, lt 3f4q)b9qe zrrd simultaneouslbrt qp)4q :i,9n ezl3fy?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open,chssc mqvci0; 4jop5,wv z cq8xr94(8 is 105 dB. What is the acoustic , v(ih j 9c rc8;mp 8q4cx4o5vszscq0wpower output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 10005 l,-e)d p1n+znqajm e Hz. The power output drops byz-+a1dnqml5epn) ej, 10 dB at 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over thesbsy9gvoep 46ks :+j5s f 3/nhir ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average humbno/3+5 ev4ygssh ps6: kjf9san ear has an effective radius of 2.0 cm. What would be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, the gan;(h: 3 xuhiqu;*2o. br;qj vks4otrh in, $\beta$ 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 iscwvamk9j,/e/n3bez 0d mx 1 z. tuned 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 cm18yltb 9 6z) ksekp2ls7frb q:sy4m/n long between fixed points with a fundamental frequency of 440 Hz and a mass per unit llspqz mk:4ls e6yb8f7b/yr1t)n2s9 k ength 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 filled with waterkec 423m6g.2 o fwgyvh (Fig. 12–35). The water level is ayf2g2 v.3g4 ckem6ohwllowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of mass 2.10 g i80(mbxh gx.kes 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 resonance (in its fux ke0m.( 8hgxbndamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one full 8h9 t.m)p u7zxvnvr lkf-p+f9loop ($\frac{1}{2}\lambda$) 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 k9 zds6xp* pv(two sources. The sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequ(zkvd p xsp9*6ency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train yln,58 ev 5qabr5fu1:, xdhi pis stationary. The conductor on the stationary train hears a 3.0-Hz beat frequenci ux58,d 55v1:blaqphnre f ,yy when the 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. Afteou69 q -jpt wyf.w0a+zo fz/.vr it jfopz.t+ v0w/6- wu. fo9ayzqpasses you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed o2c3r be1 qp8r.8v qoshlh* 6 ox;q.csvf cars just by listening to the difference in pitch of the engine noise between approaching and receding carv .sqc1cp l vb8r.h*ro6;38s 2o qxheqs. 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, soonwf .+8u wlw+unding together, produce a beat frequency of 11 Hz. The shorter one is 2.40 m long. How long is the othef+w +8.wuwlnor?    m

Two loudspeakers are at opposite end54c(:7 .t;si 6qy-4zo*nlqxonmtb haf jw m9 as 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 fro 7:mq4xy ta(.l*iontca obsj4- 69n fhwqmz;5nt of the car, (b) he is between the speakers, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in the aorta is normally aboui*r pr93 -lyzumpoc5h7u +/wst 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? Assume that the waves /p*cmir57 uhzr - lop9w3uys+travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed ut a14s). k 0uvgll4zt6.5 m/s while 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 aft)z44ts1lu aulvk 0.tger that wave reflects off the moth?    kHz

  A bat emits a series of hood *8)ag jon:s6s7jjigh frequency sound 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 the moth be detected by the bat so that the echo*adng j7s): sjjo6 8oo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig.i(n0q6cs2 wkz 12–38) was once used to send signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is 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 (sk q0wczn2i6 F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for sth56sldfrott t*.s o0w3/pkz ; ereo listening can be compromised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundt/k wodls3sfht 50;r6pzt * .oamental frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, slender njbil1 ja:69vc3th+r aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. Winrjj 6 9+:a1t il3chbvth 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 they3q 9ab36 p nfsrf+v2w threshold of hearing for the human ear at a frequency of abo3fvnbrf2yq 3w+69pasut 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 oyxt .m6y3s (8pgo.nfdsow :0 the ground hears the sonic boom 1.5 min after the plane passes directly overhead. What is the plxostyd06o og :(fwm38p.. nsyane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboaty sg)tf r2.fskk y4v-s5yrh 70 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