What is the evidence that sb5 or,l u5o2r2opj/utound travels as a wave?

What is the evidence that sounhx v0byo62owm.ha -i. d is a form of energy?

Children sometimes play wjimf(p76 y0)rjyge, lith a homemade “telephone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be0(g 6l)rjj7pe, ymif y heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air intoz )fr -jg58wnl/ aev e s+m,mermk3z/5 water, do you expect the frequency or wavelengt 5mmze+z 3/v/,le-g)8wr5jr as nkmfe h to change?

What evidence can you give that the speed of sound in airt3u.ob +8u3t q/jr gvl does not depend significantly on freqt+uo3v.rut8lgjq 3b/ uency?

The voice of a person who has inhaled helium sounds very higqxly;h+/ d4f2bu 6vlv h-pitched. Why?

How will the air temperature in a room affect the pitch of t(eg/mrfy1 *zorgan pipes?

Explain how a tube might be us-o f5e7 hapuu.ed as a filter to reduce the amplitude of sounds in various frequency ranges. (An example is a car mf ua75 .uoeph-uffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer togeh,cl--(w dtj mther as you move up the fingerboard towach( -m,-twj dlrd the bridge?

A noisy truck approaches you from behind a building. Initif rcg z1er:tkp ,ad0:bv*: ry;ally you hear it but cannot see it. When it emergestkgc:ebzy;raf*: , vd 10pr:r 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,” whereas m,orefpp)eg 32gewvk5 95 ga4 beats can be said to be due to “interfeoaepg ,3gvmgr 2pef) 9e455w krence in time.” Explain.

In Fig. 12–16, if the 4:lu ob9ke/ (cy-xsz mfrequency of the speakers were lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or closu mb:c (z9lkyex4-/oser together?

Traditional methods of protecting2 mnw(uv *jz7e; 5rs6)u pdzmg 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 not block the ambient noise. Instead, a device is used which; mug( d7w ue6p5 rj2m*vnzzs) 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 *) qrzy rqw)n tr5o0u3shown in Fig. 12–31. Each 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 component fr oqr53w ))rrz tq*n0uyequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if ,:9w:azrwwmw the source and observer move in the same direction, with the9w:rzw : ,wmaw same velocity? Explain.

If a wind is blowing, will this alter the frequency of thgdg-rd xq+oq k a5:e i(nq,t;,e sound heard by a person at rest with respect to the source? Is the wavelength or velocity cgr5ton:e xqka dg+di,; -q (q,hanged?

Figure 12–32 shows various positions of a child in motion on a swrjn,3u fz/ v8king. 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 snj f3, 8kr/vuzound of the whistle? Explain your reasoning.

  A hiker determines the vdf (,qf hps:)f/ydn4length 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 2.0p ndfh :y/)(vfdfqs, 4 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side oy o(r h17jc)lrf his ship just below the waterline. 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? As)o 7rhyr1 (jclsume 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 eo3rp1) uf3/*voc xp) erfne1 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 scxnhuv-fi . p) zh/u.rb+f2d-; hb*zdjhool of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12– n-)+z;ufdjr .h*v-hz.xu/i p2hd bbf33). 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 topy.6 7-cd ; np3we(pp st )goyma,du(. u+mzqin of a cliff. The splash it makes when striking th.gydyz +up36apt 7 enc;,mpqwn)mso u ((id.-e water below 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 the con+7 3yxyi rxl 0,xu) qfelbw7c8crete 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 e7ib w lu8x0x+yqyrx3c)lf,7impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distan 6ix8ugnbo4 :tce by the “5-second rule :8bg4outn i6x” for estimating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at thpo pv/)z2tb(fe 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 bi1h eok f ,b:7jws46qa sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when firz)n caa06s*q421 py)m6ysko qp9ss e yed simultaneously at a certain place, what will be the sound level if only one iz oks) y2 s0ymqac49 s*6e)6ppq1syans exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally noiaw .z2 qsp/qej7. iz2psy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person ex.psq7 zq .eajw/pi z22perience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas for2vu5n+5q bwhia7 6xk ku3 c0pf a CD player ia065cu+3v7xpin2h uqf kw 5kb t is 95 dB. What 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 souu2 58n9b gc-bag6qjgnnd from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered a 5uqg9g8bcgbn6n2- jon 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 anqdzgl;mmp2 ; - 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 250 W/5wk9hg8ex pd*+kr cl , while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a poix ewp gdk/krc58 *h+l9nt 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registered 130 dB when placed 2.8 m h4g4v l en6hs*in front of a lou6*ng 4 hlvh4sedspeaker 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 typicallynnno(k fp *jfc(fjt15q9+qr tj;1 o6h detect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels dipn;(6tojjn o h9r*nf1f +f(jqc q15kt ffer by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intensic a2a :j+tie4c *pq3nbc+k1pqty increase? Increase by a factor oea2aic*cnpc+:j+43 1k qbp t qf    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal di h:6usbx v tzararc na50w;*7-splacement amplitudes, but one has twice the frequency of the other. What is the 5a76w -x bsrv:0r;t*achanzuratio of their intensities?   

  What would be the sound level (in dB) of a souo qv u-t*a:-hdnd wave in air that corresponds to a u h-at-*ov:q ddisplacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what soundpm;bt n3 :+ifj level to seem as loud as a 100-Hz tone that has a 50-dB sound n ;fpitb3:j+mlevel? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when tprb*su1 cq x..he sound level is 30 dB? (See Fig. q.c br1px *us.12–6.)

  Your auditory system can accommodate a huge range of sound un,l hrk/ ( ,xrt(plw7levels. What is the ratio of hi urhx/,n pwllt7(,kr(ghest to lowest intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental frequency of 440 Hz. The length l4ls* xta i43 -g25bh,zfyi ykof thlf-5 igkza h sy*4t x3b,24ylie vibrating portion 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 cm8hmrg qht* +d) g1ln3t long. What are the fundamental and first three audible overtones if t+tr3mln )hgg1q8td*h he 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 exmx*:3)cld: i th7mndw pect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it wmw nt mh i:*cldxd3:)7as a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pl adr31x qqjww ;7)fq+ipes spanning the range of human hearing (20 Hz to 20 kHz), what w;a wqql7jdx+wq) 3f1rould 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 freq9b k* /qw4ehl9qxgpf+uency of 540 Hz as its third harmonic. What will be its fundamental frequen q+g/9f4h 9lxek *pbqwcy if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E above middlb q:oq4c;puw: 1bk y1de C (3301 :y4p cbk;bq1u:dwo q 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 em1/f)tsg nerfcr75f) oits middle C (262 Hz) when the te7r 5fe frg/o)tsc1nf) mperature 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 20;rtekfhu8k 6n(0jl+s $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Examp2;r3fb7mevr/igi-f q d w,n1dle 12–10 should the hole be that must m;wi -27f eq/f dgbinvr,d1r3 be uncovered to play D above middle C at 294 Hz?    m

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

  A particular organ pipe can resonate at 264 Hz, 440 Hz, and 616 Hz, but not bydg8hu bmy:fj/pml5+(i5l m4*t 1nuat any other freq(b5fm+4 5l: y m gp8dyuhjt*/lu1nmibuencies in between. (a) Show why this is an open or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at borm0zpufl i +cdak- u;60;sx :kth ends. It resonates at two successive harmonics of frequenciedc am6:pfl+ iurku-xz; s0k0 ;s 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 * ys0e-fp/jr7k7n2atc8d tu j$^{\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 9 vqp:-y87qmio;alb gaudible range for a 2.14-m-long organ pipe at a p7-vqo89qmyilbg;: 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. I2-s2rf;+ftku krkx q47a mia(t is open to the outside and is closed at the other end by the eardru +tairf sxkq27 fu2k-k;ra4m(m. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when tryi ,e0packq+ wb7ng to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other string?c+qaekbp 7w ,0 ±    Hz

  What is the beat frequency if middle C (262 Hz)idp43bx3 :nj25tq7ry)dzncmjz0sw 8wafk 1/ 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;6l:qf4 v vufp, while another (brand X) operates at an unknown frequency.;:vup4f6q fvl If neither whistle 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/*n w 6/zfbdq7qs when sounded with a 350-Hz tuning fork and 9 beats/s b/f67w *zqqdn when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension inuof-yj cp yz7e9jm0 efw7a.85 one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Ef08azmcp5jf9je 7oy u. -ye7wq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each tu*z:cc 4k2 npna88,vlndha. hry to play middle C (262 Hz), but one is a2nhv8 u, a8d4 n:nczca*khp l.t 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 4glm qi29)pzoc x8 p(lphku6 1341 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 posg1xm 9)i 3h(pl86c2pquol pzksible 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 f4l7klcrc23w4c nusf , s3ol;i rom one speaker and 3.50 m fro 3 lk42wcl rsnc3o4f, is;clu7m 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 piano tuner hearn hug w.3w h o+z:y1/b7uakhx;s three beats every 2.0 s when they are played together. (a)wkgo ;u+nh bxu wa3h.zyh1/:7 If one is vibrating 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 smc 7;+(xjp djmany beats per second will be heard? (Assume T =7+ (pjjmd; scx 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz when at 9ewp t2g:hq;wmcs.. jrest. What frequency do you detect if you movec j w.;g9ethp .2sw:qm with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. W 6dgcv6e;i zj1hat frequency do you detect if a fire engine whose siren emjgz6ce i;6 1vdits 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 isvfq3 0k 9biels4z88z r moving toward you at 15 m/s versus you moving toward it at 15 m/s A0vrqfbz i3ek 948sz l8re 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 same single frequency horn. When cjdka6aeih9+ j. dwtf. ydfeo3l95+,one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequeneh +5o.9le,fjc. +9daitdj d 6f 3waykcy of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 5dmrs344eq80wf dqz n3 0.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is thzqdsm n8d4frqw3e0 3 4e received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wahzp e0owx-;i jm(h3bij;4/leso 4 )ccll at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave wij)j-04p4scxb iw; ol(moi;e/z 3ehch th frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler explg4in*ch,y zgn t )0y*eriments, a tuba 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 ch*)zyg,0*4gi nln tythe station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure bvj2cemp 38tc8lood-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 leg8p8tjm ec3 v2c arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of frequency 8rv7/woy. qkg$2.25 \times10^{ 6}$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. W*9qv)j ffzwqm1c 64fh hen the wind velocity is 12 m/s from the north, what frequency will observj4qch) f1fmz*6wqf9v ers 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 moviz d(q-ga/782 2za q/ javf4r o8yqkrtvng 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 of sound is 310 m/s (a) What isa5m8hbm 5,cks the angle the shock wave makes with the direction of the airs,mb hmca5k 85plane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmosphere of a planet where the speeri.6d7xby 9y an/(+r 7s tsplud of sound is only abou/.bxpt u(y 76yd7i+ 9lss rnart 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 stri obgq+ cmx; 9s+si((:u tzyrz6kes the ocean. Determine the shock wave angle it produces yq( ; xz scu(gsr+b6 zi9t:mo+
(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 0lis w6e bg.*e$/theta$ 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 exactl-1:g1 1yaw, cirxsmmd y 1.5 km above the ground flying faster thanry 1,md1:m-x a1i gcws 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 device that sends 20,000-Hz soui kra-ckagta x8)t(40nd pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 200 m, what is raga-(c ix0takt8k)4the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there iniv1(b8uhy+ nuf1e xy0 the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewe;z9q.-a zbjle r pipe symphony. It consists of many plastic pipes ofl9;zbz .ej-a q 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 cl0gwe2 /snms+ gs 6bx:hose to the threshold of human hearing (0 dB). What will be t6gn0h swb/gm+sse: x 2he sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level+ 6d;pzy4tnvm when an 82-dB sound and an 87-dB sound are heard simultaneously? vn d 4p6z;mt+y   dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 dB. Woqw,x/iuvlj/m. * dx:ovb 18o hat is the acous vm:d8*/ioo.q,bxulj / xv1wo tic power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rat1,xhc(xm d ( 9wh2efjled at 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kH(xec,1 djh(9m2hxl wfz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typicu jsfx);; amc.p3v(arally wear protective devices over their ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be tam)x s ;(vjcruapf.;3he power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, the g r7,w ef1bc izg(mdb04ain, $\beta$ 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 tun3k0vqw wz1sut)p7 /; r*z4l rovxcpe :ed to a frequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long between fixed points with a fucu7mbg92s -mr:wa2orfykk3r .o 4 m 4indamental frequency of 440 Hz and a mass per unit length ofsmiro44 b-yakrr 3c: 2mu 29wfmo7g.k $6.1 \times10^{-4 }$ 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 abtd4ectwxrmma +:h.8hy* vw-:ove a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resrth.4 h :a*yd:w -vxe +tcm8mwonate 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 strik-f4ll 8ll 81ndsjlm5,mzg)mng 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 resonance (in its fundamental mode) with the third harmonic in the t dllfn5ll8j1,m sm4 mg)zkl-8ube?    $ \times10^{ 2}$ N

A highway overpass was /m,7kza7 kucwygwr8sunrq xp-5m82( observed 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 500–100v 7; irjb-1esw0-Hz range coming from two sources. The sound is loudest at pirwb;s je7 1-voints 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 whistl-nuf okr w(u5/es. One train is stationary. The conductor on the stationary train hears f -5r kw/ouu(na 3.0-Hz beat frequency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train w(nq ejap)8 * hb,)gylvhistle as it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the traia)g* jlpne) (,8hq yvbn moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars just by listening to r zjnp8tm s857the difference in pitch of the engine nomptjn885 s7z rise 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 ty/j;0hmm 8iv 8n rath0ogether, produce a beat frequency of 11 Hz. The shorter one is 2.40 m long. 0h a m 8/0hi8tvnyjr;mHow long is the other?    m

Two loudspeakers are at opposite ends of a railroa(d:7yxc griu7 d 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 speakeg r x(i:7d7ucyrs after they have passed him, at C?

  If the velocity of boe y3thg4c;w*mc 13) ptk tk2slood flow in the aorta is normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ult c2hpgstwt *13eko4y3 ;c)m ktrasound 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 while the moth is 7vje 1i33lju:-w vldfflying toward the bat at speed 5 m/s The bat emits a sound 37ve 3vw-ij:lj1uf dlwave of 51.35 kHz. What is the frequency of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high fre r+vs1 qkjn 3ta0-0axwquency 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 theax 3-t10a v0s+nj wqrk echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signals from onc4d oww ldz8io87i fx5a*rfq5z:8e+we 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. Theac8e5:zi7f 4oz+wwlq8 5fwdo dx r 8*i most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundamental frequency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be compromisedbez yod0q 35qzu 58nqg7 .ipp2 by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5. qz qn.3 8p5eiydz7po0u2q gb50 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamental frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, sleb jpozvf0ga // 6uce*6nder aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practicbzga/06ve cu p6 j*/foe, the rod can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the threshold of hearing for the human ear at a frequen -w:2ict99 n l50xc4tdgflxc *dakcf 7q; 1eahcy of about 1*wgxcfh9e4: ; l dqt anxd95lc17c-f2a t ki0c000 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 t/pq4i mzadwag f-5j3(.k6 pushe sonic boom 1.5 min after the plane passes directly overhead. What is the pwp-zs5p4kfi(6aqum/da3 .j glane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 15vg01veohnq *-. k qx:8.s mhjc $^{\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