What is the evidence that sound travels af e4sx41*-ekhcel + hus a wave?

What is the evidence that sound is p7v i t+j1/d,3/vyf4d uv xlija form of energy?

Children sometimes play with a homemade “telepy2dy dz js8zk v44kri8q7 70)z y3slkphone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be hearddj 2yk 7v8ks8lp y4 )70 4qzskiydz3zr 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 expect the f4 ,qpz1e qb819lqyqfk requency or wavelength to chak1p 4 eqz1q9yqq,8bf lnge?

What evidence can you give that the speed of sound in ai)8nt1hz (jxstr does not depend significantly on freque(tjzn t1s8hx )ncy?

The voice of a person who has inhaled heliumvefhtj t.er n-pa- 3(v; 6el,i sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of orm hok0*b o)be89d9kgggan pipes?

Explain how a tube might buyo2b5 8 . bxz*sdze)se used as a filter to reduce the amplitude of sounds in various frequency ranges. (An example is a car muffler s5e.8zo *x)usz2ybb d.)

Why are the frets on a guitar (Fig. 12–30) space)x9xqb uqo4l 9d closer together as you move up the fingerboard toward th 9bluq4o)x9q xe bridge?

A noisy truck approachetdp,1 f9r cr7vs you from behind a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is p7cr ,rdf19t vsuddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be dl:/5;t78qil mtqk b vtue to “interference in space,” whereas beats can betb:7i lt /k t;qm8qvl5 said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the pointunel1vp , qc)n7;o2iss D and C (where destructive and constructive int2i;v ,nenl uc)sq17poerference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people whv16om2rux i xf x.dy/2o 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 not block the ambient noise. Instead, a device is used which detects the noise, d1u.o ixvxy2 /6xrf2m 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. Eachc:,ck u rg9flpprpt *:al0q;1w xn w+* 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 (b), are the two nrp*wruckp1l0+g; walf q:p9,x:tc* component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and obs9wt/d s)4i 3,gvmkyoaerver move in the same direction, with the samemva3g/dis t k4 ,wyo9) velocity? Explain.

If a wind is blowing, wdd kov(8 -4ywkill this alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocity (8 d-voykwdk 4changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monito-/1s m9 brpexw 6sud4sr is blowing a whistle in front of the child on the grospwd x4/ bsse1r9u6-mund. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echo of her shouf1o sdx ).g-l2 s1,l3 glctyant reflected by .321 -c,yo 1ga)ss xllfdntgla cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He hears the e.:j :zf7d+ b.(xub /v womigffcho 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 7( fvjd:of:gz bwb/f+.i u.xmdoes not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the was 4gz8pij+ m 8l; jo*c3sdoc*xvelengths 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 araj9i( ;g q4olbove a school of tuna on a foggy day. Without warning, an engine backfire ocoir49 agjq l(;curs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. Theadbmzk .qusn/cg6,s(v:d- m0 splash it makes when striking the water below is hek( q bu0-m.,sz:6dgacnvdsm/ard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the co ow+7i wr+))kt2frg hhncrete pavement. A moment later two sounds are heard from tir ) h2rf+k 7o)twghw+he 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 over one mile of disrbj5p0k-negdq) 8u5ltance by the “5-second rule” for estimating the distance from a lightning strike if the t0 8ndgpq5kl u-bje5r)emperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a st0 2 iqfelyma50bb*u 6ound at the pain level of 120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of a h0+-y*h9gbkg vp.7oh6 etc nksound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level ofk zwx(-dvm q(2 95 dB when fired simultaneously at a certain place, what will be the sounkm(dqz- 2 x(vwd level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airpl h qy d67c8/dm0bh*- /ztihtw)za +iglane 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 one engine? [Hint: Add intensities,-zql/ 7t/iz 8 byg6hhwha )+ mdtc0di* not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas for6wui9lo7 m -pw a CD player it is 95 dB. W9 7wwim-6 uplohat is the ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in normalw;baze *p2m4 y conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered ow;yzb p4e* 2amn 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 eag1n /mzz hs.b1q 6.f*p t+cslmrdrum 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 rat x;jjow/1/njbryg1 e e0aj+5hed at 250 W, while the more modest amplifier B is ratnr jo;yj+/15hxge/w j a01j beed at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registered 130 dB when placed 2.8 mt i.757,4dtpqno(duxil / 0:e jrxhw b in front of a lo/7rhixi4ju5dt7.(:t wnxel o bd0q,pudspeaker 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 i2w:w2;0x2 .wy4vju uc hczdtbn sound level of 2.0 dB. What is twj cw2:zx2;bu0uyt4 . 2hvcwdhe ratio of the amplitudes 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 factor will the in ttsl kr85n p7ncda+58bl/i 2wp:u hb(tensity increase? lpbnlp t5+cn/(:sa 8t57h8wk ir ub d2Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacem .hrxj ) c))ubfafhw(50szj 1lent amplitudes, but one has twice the frequency of the other. Wha)rxbjf0 .c)jh law f )5suz1h(t is the ratio of their intensities?   

  What would be the sound level t,rn;jwa2+1 w4 nc.feg6nl uz(in dB) of a sound wave in air that corresponds to a displacement amplitude of vibratint an. fjn214cn,g+r;le6z uwwg air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound lev c*/8chw7 eytmdx5r2 +cyx kt9el to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See8ctw9 rytc+e7hcx* 5k y/mx2d Fig. 12–6.)    dB

What are the lowest and hikugqc1ae / m*2ghest frequencies that an ear can detect when the sound le2ga*c q/emku1vel is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels.lw.gkm ,u43g h What is the ratio of highest to lowest intensity at3m gw,l .hug4k
(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 of8)tsi/* r4) p vkhzdwl 440 Hz. The length of the vibrating portis rwld*i8)tv/h4) z kpon is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and firs x6xh,mh ar5b;t three audible overtones if the pipe,h a6mx; x5brh 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 frequenc 6ptx)0 hign0a4ni7spy would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tube?gtpp i0sh60a 7i4 x)nn    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 rang7e vm and2d86+rm7 xnfe of human hearing (2m na767x8d fnmv+edr2 0 Hz to 20 kHz), what would 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 cy01i-x/ nxsc as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of isx0xy-1/ c cnits original length?   Hz

  An unfingered guitar string is 0.73 m long and islu4q7c fmv2uw i7) /fy tuned to play E above middle C (330 Hz).) 7c42ywui lv ffq7/um
(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 emuzd; .eis613ov byk/mits middle C (262 Hz) when the tmz6dis.eub/voky1 3 ;emperature is 21 $^{\circ} $ C.    m
(b) What are the wavelength and frequency of the fundamental standing wave in the tube?    Hz    m
(c) What are $\lambda$ and $f$in the traveling sound wave produced in the outside air?    Hz    m

  An organ is in tune at 2 nw 7iwh yt7b4r*5* iajrjri+00 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Ex g)v6.hbsqjb) ample 12–10 should the hole be that must be uncovered to playj.hbsg)v q6)b 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 piaxi9vm 3zd xd,o21sr :pe can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any othez xv9a1:smddx r3i,o 2r 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 fx ud454u pno,is open at both ends. It resonates at two successive nfud 4p4xuo,5harmonics of frequencies 275 Hz and 330 Hz. What is
(a) the fundamental frequency,    Hz
(b) the speed of sound in the gas in the tube?$\approx$    $ \times10^{2 }$ m/s

  A pipe in air at 20 tcxty(6 p*etpjpq1x 1mj886 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 prlg qiy9(d o0u -mn ujr.-m*6vresent within the audible range for a 2.14-m-long organ pipe at jm(ov l .r0ung6dy- *im9 -uqr20 $^{\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 tc x4y;dv un;w(4kp,l j v8j5tmhe outside and is closed at the other end by the eardrum. Estimate the frequenciesyvx;4md c twk8uj5 ;p,v(ljn4 (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 two str *n+y;kv ch5c9iuzfq6ings, one of which is sounding 440 Hz. How far off in frequency is the other c*v+uk5 zqhc 6 ;n9yfistring? ±    Hz

  What is the beat frequw:k2- i0tmy zy)6azlmency if middle C (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while another (brand X;tqc/q;4m 1w w. zvjim) 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 sim1zqc4 jvmm; q/ww;i .tultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4zc 8 8a19rpl3hj6owef beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibration3efpl6rojcz8a w 8 h91al frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned01n+)0 2d1hazqwo1jey +kg)sasasql to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq.ze1l+0 s 1qo)skda+ 1ns2q) a0jwaghy 11–13.]    Hz

  How many beats will bd,l5,dt p k*use heard if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other at 25. 5d l*,pkstdu,0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C.njbw891vq/ md xm oree4zpdk33 ,+t* p Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are soundedzj83emnk *,drmp1p94ob wx /v 3d+ etq together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A person stands 3.00 m from one speaker and 3 7hef*f+kgznh bi5 l6(.5n*+75z hgle kh6 ifbf(0 m from the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating at 132 Hz, but a pianou:s 3a +azsy6bo7: vpi tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the b vaso67:y is+3paz u: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 inpimc+5am;*s0 sm c jks))3awu air. How many beats per second will be + jas0 *m )k5sscia3w ;mpc)muheard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of olx,/x in/ka .eh3 f/fa certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move w ,n/fxx3hi/.o/lekafith 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 whose sireks-v;/ .gj(jr.ub avb n emits at 1550 Hz moves at a speed of 3 a/r;u.(vjvbgjk -.bs2 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moelf522ku zau,xph 47 vving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frev7za5p 22 4x uuhlef,kquencies 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 wimf5t,rj+pi m.th 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? Asspf .mrt+5,mi jume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and :bhgmll hl bp85 :9cofc2-v27z ezmb-receives them returned from an object moving directly away from it at 25 m/s What is the received sound freo 2-c2 bzmzh-:gf9 l:vbpm7 c8h5b ellquency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the b* vohzq;2m 0exat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat heare2z*ov0 qmx;h in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on 58og6w z,n 4(qtdcy;m totue 9:sxe1m 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 beom1onde(8 :g qxy u6 4wmtzec,9 tts;5at frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound wave8l.hjcci6fk. 9g4qsus 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 scl.gc.98kjfui 6hq4 is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultr66pudg *lxv+ uasonic 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 570 Hz. When the*nf7h8y( irwx2.ju,by - vum fq) ylf;o6;tzr wind velocity is 12 m/s fqv;6wf h* x78jruf,)mzur.-n ;2 tyyily bo(from the north, what frequency will observers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object movin2 gcf;xymd, v5r,i +kh( :hpkog on 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 ofn) gdnh.:s(mvb*. fab sound is 310 m/s (a) What is the angle the shock wave makes with the direction of the airplane’s motifb.d *.m:a(g hvn bsn)on?    $^{\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 9nlbpq.r) 9 cecf.hn;v:8 oxethe thin atmosphere of a planet where the speed of sound is o9rc np;oevb.c 8hq.f9lne: )xnly about 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 mmmx+ p(-hay+m;d.x wf/s strikes the ocean. Determine the shock wave angle it p-wx f+y; x d+mp.m(hmaroduces
(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 -e +xe8m*oyk5pq g9cdu a-m r:$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a plane exactly 1.5 km above the ge vfbe3,g5o )fround flying faster than the spee bfv o5f3e,g)ed 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 device that sends 20,000-Hz sounhectbec7/p ; vp8b (,vd pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which;ppvv h/eecc7 t(b8 ,b it is designed to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many ot/29 hz7 ox amo09lhhwctaves are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pi,m5i )9lwfn l:**a,(istxk n()ed8ly y ld xbipe symphony. It consists of many plastic pipes of various l*m kn(any 9 ,i yxlb*,d)e5li(:lsd fiwl8)txengths, 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 fsqu zj+4cuk42ei 9j8(+ vkx-i9wot -sd qg /gqrom a person makes a sound close to the threshold of human hearing (0 dB). What will be the sound lg9 g 4uswqj(oti/s2kjiv9c +8z+kq4x-du-qeevel of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-dB sound are 6g y-lvp:xqkl lk14 p:heard s:llvyk l6 4pxqgp:1k-imultaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 2yzms8uj/zi,kk *r v3g b.s 7d105 dB. What is the .jdyzsg krms/z,2b7 3i* uk8v acoustic power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 10sw103xphti(. 0qahz vkov0/jcpy; * s00 Hz. The power output drops by 10 dB at 15 kHz. What is the power output in watts at 15 kHz? .*/1wqvt 0shcjz a s3;ohy(pv0xk0 ip    dB

  Workers around jet airca37v 2y duyh1 d79zv6hbdkvv3p k(x.braft typically 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. .vk dau33vk hy(dpy2167bbv x97zh vdWhat 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 gain, 1rjcp;9fuy r :$\beta$ 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 frequency 1 +r3zxu trp+ vh6-hre*dhw/i2$\frac{1}{2}$ 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 p ivhfm0v5q--v oints with a fundamental frequency of 440 Hz and a mass per unit lenhvq -v-m5 if0vgth 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)av)qha+c1er i rre u(y+t i/br8h7d6 filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning fork?)6h r )ih7 +a8rvy(e+tceqr1bui /ard    Hz

  A 75-cm-long guitar string ofi qnq jgw ,/8-5vl3vfe 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 resonance (in its fundamental mode) with 3j /eivlf8vq5n ,-wqg the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to*t d9y6g d7s3okzojk3 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 sourcea/*k in6hcv-hio0x p)s. 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 frequenoi 0h/cp hixk6-v*)a ncy of the sound?   Hz

  Two trains emit 424-Hz whcov16l(lq g(m964u g -vjwghnistles. One train is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of theq ug9m 1j (cnw4h6 lv-vgog6l( moving train?   m/s

  The frequency of a steam train whifak9x va0 :m-ael( a7 ze)b:rwstle as it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant velocitr: )fve alb7ame0awk(9a:x-zy)?    m/s

  At a race track, you can estimate the speed of cars just by l+/5 l: iuatry6-csu4hswb 4 lip( mjc7istening to the difference in pitch of the engine noise between approaching and receding cars. Suppose utm4jlc:5(/ +c7i6i4yw- p usrlas h bthe 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, p;6;qv p znxccbn-rd87 roduce a beat frequency of 11 Hz. The shorter one is 2.40 m long. How long -dxnp;n6rvzb ;8c7 c qis the other?    m

Two loudspeakers are at opposite et 8s9tyz*i 0vcs x.n4cnds 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 frequencyyv9 x.0 sti cnsct*4z8 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 fc m5 a31q0nbpulow in the aorta is normally about 0.32 m/s what beat frequency would you expecbcn5pm u 1a0q3t if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s :pu9ms43-f9 a vn(unh4ypcf z(k gs*cwhile the moth is flying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is thgnc 394(sma vp yf:n(f9p-4*kuh szcu e frequency of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequencj8) bsa6:pzfv y sound pulses as it approaches a moth. The ps8j6):fpbaz v ulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used tok*r: s ofx6wh0 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 frx6 hsr0o:w* kfequency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo lisn)ra7v 8la8 rptening 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 fundamental frequencies for the stanl aan78vrrp)8 ding waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involv9rwa zz x26w.ues 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, rina2zx .wur6wz9ging 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 uu qjppxjf6)9, g r3 2kuv1o5rhearing for the human ear at a frequency of ab,1 u5r 23 oj)ur69kxuqppfjg vout 1000 Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on the ground hears te2po -ktc5 ;p0iu6 hkthe sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s altitudkcup -ki tpo52;th 06ee?    $ \times10^{4 }$ m

  The wake of a speedboat xck1*n0b; mnykjy +b o5z2jk7is 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