What is the evidence that sound travels as a wavqz/o*n4kv0+kyw z g 1ue?

What is the evidence thah 6v*fm8td-yvu bg1v1t sound is a form of energy?

Children sometimes play with a/er,2 pps:2zhmon 0waadu/d, 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 be heard at the other cup (Fig. 12–29). Explhw:ro,pdpn/a/0, m2 suzed a2ain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you expe0-hb m:82y25 r:dhray6 lhqn/ aivuwwct the frequency or wavelength to dh 5v8r0aiy - 6urn: qwbwh2l:/y2ahmchange?

What evidence can you give that the speed of sound in air does not depxf wa lkm1y//):h+skpend significantly on fxfs1: )h/ ak/wkl+mpyrequency?

The voice of a person who has inhaled helium sounds very high-pitched. Whyoiim )y7 * oj)81pwwsh?

How will the air temperature in a room affect the pitch of organ pipes?.:l:s7qkkhc4.hsnopppi 9 7k

Explain how a tube might be used as a filter to reduce thenm*ar1z40 8syme (ei 4eb,puk amplitude of sounds in various frequency ranges. (An example ie z*uei 1ey skp,a4 b8(4rmn0ms a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you moqj ;glun3*ksnm plfimp9 ae8a)i 46 *8ve up the fingerboard towgsq 864*n3n*j)8mklp lm;i ea9 uf aipard the bridge?

A noisy truck approaches you from behind a building. Initially you hearpahrpy2,qw: fv8nk/b m3 u9x0 it but cannot see it. When it emerges and you do see it, its sounf0qh x 3v,rn/8p:yk2m apu bw9d 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 “into0b29nn2rbyzo )o7r derference in space,” whereas beats can be said to be due to “int)zobon9 0n2r 7oryd2berference in time.” Explain.

In Fig. 12–16, if the frequency of the speakeri w; +-avchf7igvo40fs were lowered, would the points D and C (where destructive and constructive i oiif-ca4+wh 7vvf ;g0nterference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people w gkp 2)6f(ujs7g.y plvho work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise v( gj7y sf pp6).k2gullevels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves s,h511v5zzef 0ie cp kshown 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 thkpe0,s 55zf1c ve1zi he waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in the same direcwvo+rw53:j(szm- seition, with the same (ivs- wz esjr5m3w :o+velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound heard by a perwuj6g eg5,7/ol( eeh fngj,o2 son at rest with respect to the source? Is the wavelength or ve,ng5fhge ljw6o,72e eg /u(o jlocity changed?

Figure 12–32 shows various positions of a child in moaxhk q6- c2 +k64+ ox/aierlrrtion on a swing. A monitor is blo6a r+-lxr xq2 e4or/kh6ai c+kwing 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? Explain your reasoning.

  A hiker determines the length of a lake by listening r u7ff ez9k77vfor the echo of her shout reflected by a cliff at the far end of the lake. She hve77f7rz ku9f ears 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 beo,5;d ax8-hm z 5ybrddlow the waterline. He hears the echo of the sound reflected from the ocear5y o5bdm,dhzx8 -a ;dn floor directly below 2.5 s later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths dm:n ck-2lto; in air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is drifting just above a school o,g 9ladm4rl 4:,j+c c fzh*ermf tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfirejhm ,*efam4d,c4 lr+zlrcg :9 is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splas1*. qj ebcu.66 ejcc,hetd h.fh it makes when striking the water below is heard 3.5 s later. How high is the clif.jj qe.d 6e.hcfc e1 6,bhuc*tf?    m

  A person, with his ear to the ground, seesm7c39ws l(ymv a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the cw9my(s 3vm l7air 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 (. s/b3xlcm nierror made over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature mi.s l(b3 c/xnis (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of 4dpwiy d1)l s/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 i6ij;gvmt6j tbv *2h 1a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultanet:+ q94tyc wlgously at a certain place, what will be the souct tylg+4:qw9nd level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance fr5u x +okxw.2wheh 4lq(cxq4( mom an airplane 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, not dB’s.]x 4+ w5cluqomk h4x2qxwh( e.(    dB

  A cassette player is said to have a signal-to-noise ra q;521y h r(rkl(so8sztdepjfc,tb / +tio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the sign2cj8/td1fte(+orhs 5 krs zl;b(y pq,al 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 normal3s7v6mrp vol. conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the mor.p76 omlvv s3uth. $\approx$    $ \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 eardrum whose area ist:0/1qtirje i $5 \times10^{ -5} m^2$ (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, while the more modest ampq8:hhgnj*; kdlifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 h;k8q dn:hgj* 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 in frowrb1c+:4 1bg idd.dpjnt of a loudspeaker on the stage.pd1b+ .:4dr1cwbjg d i
(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 st 6 hn ny)fjn8wpn7h--ound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11)8nhn jfnn-y 6ptw7-h–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by wh a/xlze;/2pksvo24e*v/ ojdw at factor will the intensity increase? Increase by a factor oesv p*o/v2z4/ kwa j2 ed;lox/f    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, bhi qtw1q gb)7,ut one has twice the frequency of the othb,qtq)7g 1iw her. What is the ratio of their intensities?   

  What would be the soundrqu s50tp)9 fx level (in dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 300 5qspr9f0x )tu Hz?    dB

  A 6000-Hz tone must have what sound rw2jc ew-.2 x08-sgpfwjb5yh level to seem as loud as a 100-Hz tone that has a 50-dB sound level? (Sep 2x-wyhg j2rwb8sw. 0-ec5j fe Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear caiglosz78cy(dgrz5th6q d + +/n detect when the sound lev dtziy l7s8h(rczgo6d+5q/+g el is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is thewv6gu70i9- wui hi zg -rtr23o ratio of r 9hi-utz2w0g io37giv6ru-w 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 a fundamental frequency of 440 Hz. The ledw+h g0-umte0ngth of the vibrating portion is 32 cm,wd t0-+0ehmg u 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 ar t3uj zl 9f e,f5dcjt2-xq(k*re the fundamental and first three audible overtoneu25(t -c3*q jjffd,zrl 9xe kts if the pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you expect frocczsr8 b5;c-uik 3g 8nm blowing across the top of an empty soda bottle c 8zcn igs;-5ucbk 3r8that is 18 cm deep, if you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pipes spannihno(z awu 0.1eng the range of human hearing (20 Hz to 20 kHz), what would be0u(neo. azwh1 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 as it/os1hktfb4n*j x/k 9os third harmonic. What will be its fundamental frequency if it is fingered at a length of only oksb j4t1 /fx o*hk/9n60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and zqfh(gc/fwc6c3cn z8pr 1. .uvp)4ey is tuned to play E above middle C (33he cfp. fz)gn /z8v. u3wc1qc6(4 rpcy0 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 emicyuegev 1)c 6vzp:v8-ts middle C (262 Hz) when the temperatuye)-v ev zc p1:8cvu6gre 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 p+uvw495w thi$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the4tr.y oong 3l 6d(0 /khyvsqv0 flute in Example 12–10 should the hole be that must g4lvh./0 or0(3y ty6vnos kq dbe 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 ko)u e 1v3i8boat 264 Hz, 440 Hz, and 616 Hz, but not at any other f8vboi eo)k13 urequencies 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 both ends. It rene 4f tq(hbemaw c4124sonates at two success 2(ew4e4 qnbt4ach1mfive harmonics 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 fi d yvx7 +mcr/x g54yd*/bbx2$^{\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 prq bvng 4-)hp)l)yzrm/esent within the audible range for a 2.14-m-long organ pl/y)v gnr 4z )p)q-bmhipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. I /chy f(8k/ljht 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 wac8/fhk/ h( yljves 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 q1:p kujl3c 9xbeat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is:c1luxp3q 9jk the other string? ±    Hz

  What is the beat frequency if middle C a 2(s+wl4lxen(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 (bra*0a(hl ir/wiznd X) operates at an unknown frequency. If neither whistle can be heard by humans ir( zl*w0a/h iwhen played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-yck(v vg6f b8dy7kky7 -br8h9Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? 9 8fck7ydh7-b8kyv(gry6b vk Explain your reasoning.    Hz

  Two violin strings are tuned to thmsnfks-/afbh64 ;e) pe same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency hesf f 6k;hnseamb-) /p4ard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play middle us)j7,m14u n ))jsg f yl7 rmtllzjq8)C (262 Hz), but one is at 5.0°C and the uztsl gu7)jj)q)sm 1f,8mly 7)nr 4jl other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a fre8yq +uc 32 p00ewx.rurif)emo7o4hup quency 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 frequencp 8u0.xhieru 4)+2cpfu3 o0eoqrym7 wy 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 3.00 6qm726al4 oq4r gitrq.x we3ze +jk x*m from one speaker and 3.50 m from .el4q+ 26i*7 aqq3wxogzt erkrx64 mjthe 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 v qt-go tl(r/5iibrating at 132 Hz, but a piano tuner hears three bego(5/l -rqittats every 2.0 s when they are played together. (a) 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 wpm4 qfqbxkt 4;p(; (kcavelengths 2.64 m and 2.76 m in air. How many beats per second wil((pcbk;f4 kxqtpmq; 4l be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engigs tspy 1/m0n4ne’s siren is 1550 Hz when at rest. What frequency do you detec sm/nsy 104tgpt if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you dety;/s kmr-usevncgv084s14 joect if a fire engine whose siren emits at 1550 Hz moves at a speeogsr4m e-4cjn8 uv0y;kv/ ss1 d 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 nq- xbb4r wjckm5t*d4741li qmoving toward you at 171jbknq5rbqlxd4iwmtc * 44 -5 m/s versus you moving toward it at 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 one is 0c izmh5)qdx (w5u jupg7w1m+at rest and the other is moving toward the first at 15 m/s the driver at rest hear j5quigp d7+0xz15mw)w(h umcs 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 waven4qt1 ,aod)h ,r(cnnns at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the re1,n)q,noa(4rnn c htdceived sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it fit)m7azg g( 1slies, the bat emits an ultrasonicg tza)s 71(img sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was pwxkpjh+yew4u +mo1 /9layed 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 +e/o+hyw91 p xmuwkj4 the railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeds. comcam ; f5turf(;a4,Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound somft (mc,ru ;4a5;afoc urce?   Hz

  The Doppler effect using ultrasonic waves of f lcci. o,l - bf,e.4 jccvof1yf4l3b/jrequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequency 570 Hz. When the wind velocity ye) h -kuacm72i4p/gzis 12 m/s from the north, what frequency will observers hear who are located, at reszhc7 pm2uei/ya)- k4gt,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if its slhht at.xt1:* peed 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 Mach8. vk,lsbu*u- j7 pag ,ecuiasft-o97 2.3 where the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the directionpulagc j* st9 euos -k-,ufa7v,b.i7 8 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 thcplx 72:)yvwsin atmosphere of a planet where the speed of sound is only about 35 m/s s)cx2y:lvwp 7
(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. Determindh,y7c/pf ) 6vaycgf 0e the shock wave angle g f7d0hyvy 6/)cafc,pit produces
(a) in the air just before entering the ocean, $\approx$    (Round to the nearest integer)
(b) in the water just after entering.    $^{\circ} $
Assume T = 20 $^{\circ} $C

Show that the angle rsj9aqk,sdrc /rg a7j6u9: m+ $/theta$ 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 grou:2ii+hl4e8xb 3f wpulnd flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a hor iw :fl+ epib4xlh2u38izontal 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 sendheo) 7 :tzc)3dmb tyh4gp1g-us 20,000-Hz sound pulses downward from the bottom of the boat,dmhobgttcu7pzy)) h -41g:e3 and then detects echoes. If the maximum depth for which it is designed to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible range?n/ h,ng nu.fk/ $\approx$    octaves (Round to the nearest integer)

  A science museum has a display calletl3nb v707nf vu.b(lod a sewer pipe symphony. It consists of many plastic pipes of 3(vfo7.n0b7tlbvlun 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 .ja9zw7g0a-:mc s +q xhav-sb a sound close to the threshold of human hearing (0 dB). What wilaa0c.a-qj7gbs swhvz -+x9m : l be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level whv,su y5g7 /lgjw8 o7pgen an 82-dB sound and an 87-dB sound are heard ogsplyjwg 8/,v75 7ugsimultaneously?    dB

  The sound level 12.0 m from ar2f(ek:bms 7.ardp/4d qj s0y loudspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the speaker, assuming it radiates equally in all directions? s4:7sb(/rd0d f2eykm p.rjqa    W

  A stereo amplifier is rated at 150 W outdu kfx s-,xs 9w,lcb51n 4aem2put at 1000 Hz. The power output drops bywn5ex-scb41k2x ,f9,als um d 10 dB at 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over their t0qx) tk-kv,9xrz;;8 mrye 4n7u tkey ears. Assume that the sound levrn),yqx7ytt x;z eme; 89r4kkv -ut0k el 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 intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, the gaih,n,nf3-dg pn19 noi33zc peg zui4+mn, $\beta$ 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 8axlxrxys x+ a+ e,e3a-v; *xt+uda3n1$\frac{1}{2}$ 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 mdg /3vhc3 zv gp3ja0(b.+blb:m0q asis 32 cm long between fixed points with a fundamental frequency of 44003avbd0lqhgjbm+b (3vm/ pag3. :czs Hz and a mass 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 aistn4i/ z282/u qkanzbove a vertical open tube filled with water (Fig. 12–35). The water l/ 8ink nz2az2/tqsiu4 evel 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?   Hz

  A 75-cm-long guitar string of mass 2.10 g is near a tube that is open ao/pzg,4ca* ncl76cjv t one end and also 75 cm long. How much tension should be in 6p jzg4/ccl,*nv7 aoc 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 observed to resonate as one full g ;x::3ftp7l1 4lpc(ykty e neloop ($\frac{1}{2}\lambda$) 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 7fclmskh n9:;pkt 4:kf9tw b6-Hz range coming from two sources. The sound is loudest at points equidistant from the two sources kh f4t;m c nfw7k9:9t:bsklp6. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. Thev tr6u*mh ks1) conductor on the stationary train hears a 3.0-Hz beat frvsutr)h k m16*equency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approaches you is 538 Hz. Aftj u:;x)bbj7kier it passes you, its frequency is measured as 486 Hz. How fast was theji)u ;jk7:xb b train moving (assume constant velocity)?    m/s

  At a race track, you can esti9ru/imo i*cx,p9 b)zw mate 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 octave (frequency halved) as it goes by on the str 9mbc) uoxpi9zw,i/r *aightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11 sk3 r5fxade 4xa .cz99utp -*xHz. The shorter one is 2.40 m long. Hox-.p9fe 9ursax3 5xtzc*4 akdw long is the other?    m

Two loudspeakers are3+eoui,zd7j )yfcua 8t;gycmp7w 5o n3zn;d 0 at opposite ends of a railroad car as it moves past a stationary obsero 87ngtu0emyy7;wjcu z3fcod35)aip +z ,; nd ver at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listens from the position A, in front of the car, (b) he is between the speakers, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in the aorta is normally s fk.rdi;r0: (mnlt p+about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speedtif(d+ .nslmp:k0;rr of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s while theqt3 ;osjp 1ns+ 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 res; tp3qs+jon1 flects off the moth?    kHz

  A bat emits a series of high frequelcymvmn*r c/c0q -8.z*c cqa-ncy sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo mqcc. 0m y-anzr-8*cv*lcc /qfrom one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send sige311 g)pea qkol7 hmy)vq/7fwnals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create qy )f1 /kqhom a17elp)3vew 7gdeep 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 an open tube.

  Room acoustics for stereo listening can be compromised by the presence of s-xy:p44dnm*xzb ki cnsv uy 1..*fqq4tanding waves, which can cause acoustic “x qvf *yis: d4 4mb..ny-zcup4*kxqn1dead 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 standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, slender aluminu4e;i; b9mot tum 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 madt;euo b9 mit;4e 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 frequenc5hivf nj*2;iky of about 1000 Hz is n2 h jvii;*k5f$I_0$ = $1 \times10^{12 } W / m^2$ 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 hea0lvzqm5da+yp4 yboem.zc*8 5,abf n ,wkb 17qrs the sonic boom 1.5 min after the plaz +4m b,5.d f *0wbka,olyym8a7 vp15qbqcen zne passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 15 e 6sh/rfl- v 5 )kjij:*wm7crm csj)5h$^{\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