What is the evidence that s)vt(g uh+ q(ptound travels as a wave?

What is the evidence that soungxv ;lofpci +6l4c..m /x0oypxe ( m.rd is a form of energy?

Children sometimes play with a homemade “telephone” by a +/s7n6kwnxpzt e; zp8ttaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the p zs+knz8nwx;7 t/ 6peother cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave patc(op8j- v0 wqsses from air into water, do you expect the frequency or wavelength to cha0-wtjv c8opq( nge?

What evidence can you 07 7/-c :qkvk:j l esr 5)jpjks1phpsdgive that the speed of sound in air does not depend significantly on frequer0ec1 hp j5kd:jps7p /j slk7s-:qv)kncy?

The voice of a person who has inhaled heliuy e- l672lik)tp*646lrc obtgabv)b sm sounds very high-pitched. Why?

How will the air temperature in a room 3 0v w--dsn7k9wwqumg affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitud5)ub tk8;lrrje of sounds in various frequency ranges. (An example is a car muff)8 r ;u5ktjrlbler.)

Why are the frets on a guitar (Fig. 12–30) spac01d-v 3 k*ltqjo*b rjeed closer together as you move up the fingertbjlev10o**3 -dj qr kboard toward the bridge?

A noisy truck approaches you fromtt)1+seew qh5 behind a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the t1+qs ehwte 5)high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whereagy )x(g-0p rxvxj sv/-s beats can be said to be due to “interference in time.” Ex--x vv( )/yxxsgp g0jrplain.

In Fig. 12–16, if the frequency of the speakers were lowe ir fs6ti5gq86l2ajw*;lh 5gfred, would the points D and C (where destructive and constructive interference occur) move farthefjtf q2s6h w ;li a8r5ig*56glr apart or closer together?

Traditional methods of protecting the hearing of people i0pd+ db2 e5dfwho work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new tef2+ddd50bi e pchnology, 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 betteg8+i(x5 81g pjwx h thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18.tt81i+gx8 (p j5ghe xw In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the sourcewm5n kcf9w0 b/ and observer move in the same direction, 0knw5 9m/cfbwwith the same velocity? Explain.

If a wind is blowing, will this + qnhd/zb3+q jalter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocity changedj +n3qd/b qh+z?

Figure 12–32 shows various positions of a child in motion on a swing.0jvxy; swzh ww13o ;nm) yfx3o*97 vcr 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 whistle? Explaz7 w0rx3 ym1wwc9o fs;;y*h)ojx3v vn in your reasoning.

  A hiker determines the length of a lake by listening for t dk 1f0pgfy66ihe echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. p0y 6ifd6g1k f$\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He hkkb xi /;zjq m0m9yw2(ears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Tabley;/bqx9 wmzm( kkj2i0 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air atg t*dpqu))que (vx,5br6 /xqq 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 vu.7f +kb11deu twlilz9vb9vf 98x c( a school of tuna on a foggy day. Without warning, an engine bac.(79 l81ef kvx1bv vuw9uzd+9tiflbckfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The spl7f6g7o9p g0ivw,dye r6/z ol wash it makes when striking the water below is g,/w o9p6ew7v0 7fdry6 liozgheard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, see5mv9og n ;l/uts a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How ;ov95l/ug m tnfar away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one m8 3cz v+ wcqagnmuao81.u. k8gile of distance by the “5-second rule” for estimatincv.1no83gg.awquu k8 a zcm8+g the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity *m( s8,) 0ptobjktrmzof a sound 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 sound whose intensityv;lax (o q58.;ysghj g is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when firedx2d ycn-7wtm23l1poe simultaneously at a certain place, what will be xmd3wltyc272 n-1p eothe sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equaj8.m tc fm5d/r;h fz:glly noisy jet engines is experiencic8:f5.zh ;jt/d mmr gfng 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, not dB’s.]    dB

  A cassette player is said to have a sign7mg9 jjej- g; rmkx 0j)k+qoe2al-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background nok-2rgoq+0xjj9 eme7jm; jk) gise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the poweb)boxq +s6 bp 0pv0d3yr output of sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughl yvpo +b6 qxb0p)d0b3sy uniformly over a sphere centered on the mouth. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave strikes an g(mo b0jpdq20eardrum 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 ic .f yv*yotb/zw7p)d8s rated at 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a pointyypd/7cot )vz* 8.wfb 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 mjz0+ yp; mb5ygeter registered 130 dB when placed 2.8 m in front of a y5bg;0p myz +jloudspeaker on the stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound level of 2.0 dB. What0 ighznf h s1kzn4qp3q :r7.wj(9 f5db is the ratio of the a3fhdwkzjf s:5qhn ng 1qrz 790.b4p(implitudes 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 will7emas)cygc p8 lp *6p. the intensity 6a y )ceg 78s.p*plmpcincrease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplit idqr81*ia sug/o o*0eudes, but one has twice the frequency of the other. What is the ratio of their intensitie1ir* a/seoq8igdo*0 us?   

  What would be the sound level (in dB) of a sound wavez li//gcm**aw in air that corresponds to a displacement amplitude of vibrating air moleli/a/c g z*w*mcules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must hba 16n2ln0/r d+oh1ib/b kyrhave what sound level to seem as loud as a 100-Hz tone that has a 50-dB sound n+ab0 d1/ kby/12ilnrho hr6b level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencicbvlf0+ 3.(.u0 sftxghhoa9 +s5 jdcyes that an ear can detect when the sound level is 30 dB? (See Fig. 1t gb0. +oua hj 5ds.c0c3f(9fylhsvx+ 2–6.)

  Your auditory system can accommodate a huge *n (-loc9ijszps i w2 k;(:laerange of sound levels. What is the ratio oawcnsk iz lol se:-i *;j9p(2(f highest 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 4,1e b*n(sjccemlsp l;b3dr. a fundamental frequency of 440 Hz. The length of the vibrating portion i cd.eep3b1, cbrssnll4 ;m(*js 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 u q+3:dxfy: by/fkua ;zq9o0rare the fundamental and first three audible overtones if the9qu;:a/ 0uxfkd+3: rfo yqb zy 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 expect from blowing across pd5,fr uj hbnr0sq..; the top of an empty soda bottle that is 18 cm deep, if you assumed it was ufj.rnh;0p.rb5 s,qd a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pipes spanning the ran;z8cj 9wv( pin i7m q/zap4(ctge of human hearing (20 Hz to 20 kHz), what would be the 4p8(cct in;a m(z v7 wjpi9q/zrange of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third hrn:u o4i.m)h oarmonic. What will be its fundamental frequency if it is fingered at a length of n4i romoh u):.only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m1d):keganh)0p ncr d . long and is tuned to play E above middle C ( )p:aenncd)0r.1g dk h330 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 org 6.7 gegx,ittian pipe that emits middle C (262 Hz) when the ttgi 6gx.,ti 7eemperature 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 a84dxjyk, j g*mt 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in qpbr4m0i8 frs;ew j(9Example 12–10 should the hole be that must be uncovered to pl(pfwm4ri;bes q 09 8rjay 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 att rt8)lqf0qm( 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or a closed pi 8mqft(0l) rtqpe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at both ends. It resonat*1jzn w-v vt covp/h+(es at two successive harmonics of frequencies 2v-oc1(vv/pj* nw+z th75 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 q 46bj l cwjngu92y *f0uajj13$^{\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 fold8 az.g 8qdc*oaur 7/r a 2.14-m-long organ pipe a8 7* ugoalz daq/.c8drt 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal l5wy*yy *3kjnga+x en.px:j)is approximately 2.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves 3p*x+5 gyywy)jkan:.nj l*exin 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 sdcar:1 y lx owjtt(5e9bnm+(3hqk8.v when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other r e.b m t+tahv5qc(38ok( 19x: lwjdnystring? ±    Hz

  What is the beat frequency i*)e5q,nf /y8b-nb uu; gw8gwnml ke)hf 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 anothex s6( a: wr,co,*hoitzr (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X. ,t zowhi( :c*rx, aos6   kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork and u8aod 7ix7o/ l/xko3f9 beats/s when sound8d7kx7l/ o i/xu 3oafoed with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tune2gd9mdn nx (3pd 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 togethe (3 dndmxn9pg2r? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each oh3 6g p94fk 9yhl,oqqtry to play middle C (262 Hz), but ,pk6oh fql4h3og9 y9 qone is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and 3nib+rdq9y,fC. 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, tib9 3qy,fdn+rhe beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A person stands 3.05 e4bi v4 ubbcs u7dwx2us-;j)0 m from one speaker and 3.50e sucbu jibbv)2d-; sw5 4xu47 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 piano tuner h 1p2robbf h9;qmayv9mgc1:-l ears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, w19o-vqlb :b2 y;m cpr9fha1m ghat 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 andtv 7qjs,8,lqb 2.76 m in air. How many beats per second will be hear8 tqqb,l,7s vjd? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency *jgzbrnr;3)pof a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30 m/s )3;zgrb rp nj*
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequv:mn2jn.kg;mc8mu9 c+ btt/ vency do you detect if a fire engine whose siren emits atnnmv/ c2v+t89:b; kmtmc j.gu 1550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is os jav8hn+ s(81palh- moving toward you at 15 m/s versus you moving toward it atss h8-h(a +o na8ljv1p 15 m/s Are 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 os 1 l3ybyxi;wajb9q56ne is at resila1 wy3x 6y5bj9sb;q t 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? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz a/lse+-ieh8u and receives them returned from an object-ieuh/ae8sl + moving directly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed offvt,dy7x5py :*se d1m 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected waveepyds,fxy75 mdv :1t*?    $ \times10^{4}$ Hz

  In one of the original Doppler(wk7t lj dy22b experiments, 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 stationt7w(2yj2 bk ld. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measvbik 0 85x:i w6l(tllusheo9)xm9q5 cure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to oh5mlwiiscvt6l ) xb99u x :l(keq058be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic wav*r 0dgm+6 wzazsi7+a ves 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 thet ,r4m- vox*k (bd*xf q(abnt65 xzp/l6wz;d a wind velocity is 12 m/s from the north, w q5k bd(f/66rn* ,ox(wapt mv 4 xtda*xz;bl-zhat 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 movinsp v:09blhr(i xf4pz* g 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 3u 1mcut hxrt- n40ng4 5yjmp;+10 m/s (a) What is the angle the shock wave mak5ctpxmyhjn+u0mtu 1n4;g- r4 es with the direction of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmosphere of a planet where the speeda vb)ldm8x) 8y of sound is only ax)88 bmv)ayld bout 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 strikes the ocean. Determine the s02n gftd2-d*a; 0 keavbjnb-shock wave angle it prodd;gnt - 2a0dak* jbfs-n 0be2vuces
(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 jl + g-t(ub8 w5ym ffk0 g:bjjhk7o,u.$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a pl5.c, jvy yww7kmf lm9+k(us6wane exactly 1.5 km above the ground flying faster than the speed of sound. By the t 5 sc6wvu(jykmwm7. 9fkylw+,ime 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 niry rl )p)4fn95 c3rjsound pulses downward from the bottom of the boat, and then detects echoes. Ip fj4nr l)i59nyc)3rr f the maximum depth for which it is designed to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many(b2c. mft (d/vy) fbrs/ctk h)kbu)h9 octaves are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consist+qrh7s+r +5dl5 rvztes of many plastic pipes of various lengths, which are open on both5z+ t+ehsq7lr +5 dvrr 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 9enpti /ef0oap0f (hew3d* 0j the threshold of human hearing (0 dB). What will be the sound level of 10 0fp/ie atp e0*3eo9j0(dhwfn00 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB soundsggwn.q4s1;whou6z;m i y5p1 and an 87-dB sound are heard sim. swuz o6nh1; gpy415q;giswm ultaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in thvm. rxc 0(yzkr5xe/a(e open, is 105 dB. What is the acoustic power output (W) of the speaker, assuming it radiates equally ixkc/(mxy v (ra0. er5zn all directions?    W

  A stereo amplifier is rated al5 esg:ir+-qet 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power output in es5- qgli:+erwatts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devir b6 g; ompjw8bz*fvwy+-,zt8 ces over their ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the power interceptew8 b +;8w6f o-mvrtzb,ygp*zj d by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communicat rflqrqb8,7lx3zgx ;.z8 :ytf ions systems, the gain, $\beta$ in decibels is defined as
$\beta$ = 10log($\frac{P_{out}}{P_{in}}$)
where $P_{in}$ is the power input to the system and $P_{out}$ is the power output. A particular stereo amplifier puts out 100 W of power for an input of 1 mW. What is its gain in dB?   dB

  Each string on a violin i+cqm2)e +l z5as0 cpifs 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 cm long bequxf8 f)kegype/10a lt5 m ez ,d-37aatween fixed points with a fundamental frequency of 440 Hz and a ma 5m x3/qpf )ef81-ga l0ktuda,aeye7zss per unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration above a vertical open tube filled xibro zv-kb s1e)e7; ui)e.b2 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 ub;.b si))bkz v ier2x1e7-eothe 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.(fbntt3*u 5ogw(vaw ( (s7 mbd10 g is near a tube that is open at one end and asm ( w( td7(ub5abw vtofn*3g(lso 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 tube?    $ \times10^{ 2}$ N

A highway overpass was observe)byqxy5m -w q/d uudq6 taw8)5d to resonate as one full loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz range coming from two sourcesewax1iqr 80a wsd j6/1. The sound is loudest at points equidistant from the two sources. To determines6ww1jaar1 x8/0eqi d 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 whistlov8/vqiat luaa2xsf*r ; g +84es. 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 sper8q* v vxoi aat;/ lag2u8+f4sed of the moving train?   m/s

  The frequency of a steam traisjkw+uo .r6r *n whistle as it approaches you is 538 Hz. After it passes you, its frequency is measuredu js*w+r.6rko as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can es*w.u b34 lxlel*vk3qi;ap. xptimate the speed of cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full o;w .3l.ixu*3*4klbe q v aplpxctave (frequency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, prod;uzo 1wj7svmu4 8qyx+uce a beat frequency of 11 Hz. The short ;+u8w 1xuz4myjos7 qver one is 2.40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of a railroadsd* mqry)e,a ta+p(9m 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 thmaa(t* 9+pysdrq m)e,e 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 bloodl/4-ieak1i: x,k om*v/yn/oat1 cyv o flow in the aorta is normally about 0.32 m/s what beat frequency would yo/ik e 1:4ymtcvx-aykoi1v/,/al*on ou expect 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 muzjow 8 )3e*lnwuean1h kxx).n33 iv; /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 after that wave reflects off the mothwnh8neeu 13io3.3u) )* avxjl;zxwkn?    kHz

  A bat emits a series of high frequenb4 0o k9cdky9-hs6jxx cy sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apasb 9cokd0y9kx j h6-4xrt, 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 to send signals from on,q duo3zkmn 3dgnj; lyo*g+jlta* .k03 1lku /e 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 F sharp? (See Table 12–3.) Model as 3l g*k+l,0d.ol *n kz3mongk/ duq1u;ajytj 3 an open tube.

  Room acoustics for stereo listening can be compromised by the presence of sta lh+dq :(bt xm01xw+mlnding waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a livi(dtx++q b mwxlhml :10ng room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamental frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, slender alumi5z)(qa q: lgcdnum dg qc:5q)a(zl rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod,
(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 h p5pu6+8a5 eeh 2pidrpuman ear at a frequency of about 1006pp d85hper+u a2 5ipe0 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 Mac kdkf2 i6p*q/1:pu j7ul.c(p sc w.xxwh 2.0. An observer on the ground hears the sonic boom 1.5 min after the plane passes ddw:u7ixp/p cjpcq1 6 xwlks..f*u 2k(irectly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat i(x ( vu79(7iybkdm o.1r-zir(3u d yjrx0gzsrs 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