What is the evidence tgg ;lu77y/5:xwwh 9cnc e.lxy hat sound travels as a wave?

What is the evidence that soun6i s xon n+r1/m ys21xfb(3gbfd is a form of energy?

Children sometimes play with a homemade ,t3y;dz;s-,c / l5b142c w4pysc e k uieaxvyr“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 z4bk a;it5cey u,swy c sv214,/-edryc ;l3pxthe other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you expect *; g f1lmjuurcec(2*rthe frequency or wavelenj*lr(mce; u u*f g12rcgth to change?

What evidence can you give that the speg .p3cf6lde 0ned of sound in air does not depend significantly on frequency?gfld np63c .0e

The voice of a person who has inhaled helium sounds vl95tr 14nwyhu*: fekwbz zygq. 2q26yery high-pitched. Why?

How will the air temperature in a room affect the pitch -2c +6le jumzrdom; /5tz8uox of organ pipes?

Explain how a tube might be used(3o *pmygb9q wr lgklj1z* +4d as a filter to reduce the amplitude of sounds in various frequency rang4 3rgyp gq 9jl1*(m *lzbw+dokes. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together agvw/,d hmj( e/s you move up the fingerboard t(//j,egh dwvmoward the bridge?

A noisy truck approaches you from fh 1/xhm *n9(wis-uhs1yqn g1behind 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 q 9hng*hfnyu1-s m1(sx /iw1hthe high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whereas beai9rak)n g9hs0( j ec)lch -9myts can be said to be due to “interfe)icyhlc 0kr(h9 99ejs)m -ga nrence in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, wouldpzb)r4)betvc si z099 xje4yadm7s2 : 8vv 8rk the points D and C (where destructive and constructive interference occur) move farther apart or closer togercb8z 7b2v sv sjd8p9tkyv)eim:4r 9 xza 4)0ether?

Traditional methods of protecting the hearing of pe2vtehs+ 0jue46 l2 qtjople 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 detects the noise, inverts it electronically, then feeds i s6 42jvtehlqu+ jet02t to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be n-k6m, 1k kiqt1wtr;p 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 it116q m;wkpn -krt,k frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source 3jv -wg glub4c, bq;2:vs sxa5and observer move in the same direction, with the same vgb j:bu52 q4slw;,-a3vxv cg selocity? Explain.

If a wind is blowing, will this alter the frequency of theg4up;b nk2tle /bwldid2 6,f+s1 bh m3 sound heard by a person a2d+6,s k/ul4 bmbd2n1iw3lhp;g ebf tt rest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on s x)gaipxa7q*sx4e69a swing. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explai q*sx9ig)ap47s xxa6e n your reasoning.

  A hiker determines the length of wjfzsg84 h): ma lake by listening for the echo of her shout reflected by a cliff at th fj)z: s8gwm4he far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below /5 cshl/n9dep y w/m2rthe 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? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significa/h /y c9n/drl5pem2wsntly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air at a xsm5li0/ni (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 dr,oak+f8f :oi cifting just above a school of 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 backfire is heard:a ,fk8io c+fo (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a clj ;ix)ptathlk7h19v1 iff. The splash it makes when striking the water below is heard 3h)l7ti91p xt ; akj1hv.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the coluh5ei rm 3gi, 3,:c,g lk .ptbq55k.fxuiq,bncrete 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:3i3i,,tlr . pfe,kq h5 qlxikgb5.bu5umgc, the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent ehp y8lq+gi1crn (c /:jrror made over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the l gijpcy cr18n+q/(:htemperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensitcq2g; 7 1agaroy of 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 0xw5x4l 3 fvc5a 2qeifyejb39 of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound levqawpftsk+h w/k5y6 / 0a;rob2el of 95 dB when fired simultaneously at a certain plhry fwa5kts6//bw2;0+ kpo a qace, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane4m1 )ddbnhq ;8 qcyx:i9p tn2oez5.ls 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,qo.e41slb x yh; dtmq zn5d89)n ip:2c not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whersmo fth512a9z lp,y6xcv at-6 lv)d: yeas for a CD player it is 95 dB. What is the ratio of intensities of the signal al -potv 6z619lh)25 y,mvx:dt cfysaand the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the powe mexf3 6m;o-fyr output of sound from a person speaking in normal conversation. Use Table 12–2. Asf 3mexmf6-y ;osume the sound spreads roughly 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 u8l wh33tfkwg42wfu6f 1sw7d an 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, while the more modest amplifier B ;g3 ;+ jd gyexcn- i6sy)tav3iis rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.-+3;c njvsa g3 )ex;yi digty6$I_{250}$ =    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 dkz:fs/ rkh v.ry xy*(9B when placed 2.8 m in front of a loudspeakes(y.: ry* v/z9kkfh rxr 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 difdhew+i ierp:ai5t(1,8qhp o3 ference in sound level of 2.0 dB. What is the ratio of the amplite:ih pi 5iraphw+q e(3, 1od8tudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is trk axk ;e15f*qku sgat3bx+4 e9ipled, (a) by what factor will the intensity xgft4 uke5ebakx3 ks1*q; 9+a increase? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one 1jal h1 f;i*m2c a6befhas twice the frequency of the othhe*m i af21cba; 6l1fjer. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air ,w 03-5nh1nhdt 86qyqnmi sgmthat corresponds to a displacement amplituymihdmw-6nns3q 580 g nt,hq1 de of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what s3 xb 3i+uoe( ak)cdi.ibz x:w/ound level to seem as loud as a 100-Hz tone that has a 50-dB sound leo.z /b kidbx3:+3iicxa) (wuevel? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detecmk;a vp 6ghe1 s0(3 (y/pnh)c wuwf,sat when the sound levvgauc6eap n/pw0mw((13;yhfh s ,sk)el is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is t xdw m 9j6j.wwk;+hx;8kr* tzqhe ratio of highew9*mwxr ;.tqd; 6h8k+xzj wjkst 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 44rq u lh.kr)+;xoa6 xy30 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be plauqx o . kahr;r63+y)xlced?    N

  An organ pipe is 112 cm long. Whzf n62 -1qngdwat are the fundamental and first three audible overtones2q-dn6 fzn w1g 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 expe,9 r5f(srv;3na3u pityyidr-ktfc3 (hi- 6 slct from blowing across the top of an empty soda bottle that is 18s-fs9t 3,6 p;y3-churvi ikindry(a(5rf 3tl 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 spanning the rangevkt2c70rd3z0 vw dpt77 ovk(kp ew00t of human hearing (20 Hz to 20 kHz), what pe3 kt0k0tvdzo0d 7pvc02wrt7(7w kv would be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its: )sr90xifolc tba9 g,+e pv;e third harmonic. What will be its fundamental frequency ia9 r ;vp:e fgbxt+ o,0els9)cif it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m lo07*p vkkb3eey u qsk(;ng and is tuned to play E above middle C(k ;vup q 0e*kb3ey7sk (330 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 pi6 ,ygl mwszy+v7vpm 697nkf.bpe that emits middle C (262 Hz) when the temperature is 21n7zg 6l pyvk6 +mf7 w.9vyms,b $^{\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 k icwb1xp *l;ay 0d6k520 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Example 12–10 should the hole be t.e:r6lat k9vcpz d7 d;hat must be uncovered to play D abov6k . dlr apvz79:etcd;e 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 wj f9l ;bc ;e8)q1kvg/bvsk3enot at any other frequencies in between. (a) Show why this is an open or8)vjg3 ee;bv/ bk slw ;qcfk19 a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m lsf-9k yrs3rji/*gpts * vh:0eong is open at both ends. It resonates at two successive harmonics of frequencies 275 Hz anjhgefr-v/ :0 stk s*ips93*yrd 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 ok8s 3vy jt .e7ccj5k($^{\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 audibl ;v)j0iq9qxw qmyt:2r e range for a 2.14-m-long organ pipe a ;r9ywq)qvqji0:xm2 tt 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is avl( (c1ja jt8.f;cb v/bkw tj6pproximately 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 in the ear canal. What is the relationship of your answer to the information ic vbfa;(wt6 /.j( kt 1jcbjl8vn the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every,n jpuglt :0o/ 2.0 s when trying to adjust two strings, one of which isgn0 tplo/, u:j sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle ;4gr7 ph cmlesx1d97 oC (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 anothep/rgg, r)(d* y;xl.-mhu wbyc l6 u b+ysf0p3pr (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 arewu lcr- hg3xg;py)+ l,d.*ufsyb(/p6 mprb0y played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork y dk7 .9yeopre2+w or9and 9 beats/s when sounded with a 355-Hz tuning fork. kero 2ow79 9dy.+pery What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. t9 xks8uhw8(dThe tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played toget8t9dshkx u(8 wher? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if tw 1+ lnqp v)6:v7fgeayho identical flutes each try to play middle C (262 Hz), but one is at 5.0°C a6)g 1 nhap+7lyvvf q:end the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 44+qkpn; * ,wo:qm.bxp mds8 s5k1 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are .n;qmkkm5 +xpqs:8 p,dosw*bsounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are 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 persh5rff82swcwqc;qa )2 on stands 3.00 m from one speaker and 3.50 m from the other.a5rf 2cqh2f q8 wsw);c
(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 pizo 3um2blcn; qg43dm1ano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what b1 qg3udcl;m o2 nm34zmust 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 (wr 4wuj,sl3s wavelengths 2.64 m and 2.76 m in air. How many beats per seconsrl, 3(4 juswwd will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a vgpbee ;-8pe) certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect iee );vpbe- gp8f 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 dg)w;x.okw u4 ketect if a fire engine whose siren emits at 1550 Hz moves .gox 4u;wwk)kat 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 moving towaszk-,c0 sfwa-6t: xi5 ktbd s*rd you at 15 m/s versus you moving toward it at 15 m/s ts ,wf *sk -ib-zcstd06:5axkAre 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:13wsl 9i 69d/oj ,ainqmenuj the same single frequency horn. When one is at rest and the other is moving toward the first at 15 m/sj:3ao/u isi6mn w9jq, dl91ne 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 ultrasonic6762 r/jdm g jsc1wutn sound waves at 50.0 kHz and receives them returned from an object moving directly 21w dru67ng mts/ jc6jaway from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat emitxp*o5) 8xs v3ebzt3 yg9x ya1zs an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave? p83ze1xxt9bg3y zyvs a *ox5)   $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving flat 7 c,*fi*;6pwivkkdft 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 approachefw7*6 k d;fpiv,* ctikd the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flo k6r wlsr(kw-7w 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 (rw-k7lr ws k6leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of frequency i+ao)3 w7uaz+a * uipu$2.25 \times10^{ 6}$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 emitsh)g4byd grai + ;.ph y:w-cu6s sound of frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are located, agw.-ra4+ cp )u 6iy;dybghsh:t 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 moving on lajise4vu hx ,1n,qgv*bs./w 7t5 zf8land 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 s *h p;-;*y5xdxy0;rr:zp0rp pwqhqe eound is 310 m/s (a) What is the angle the shock wave makes with the direction of thx- h *r;:ppqhyzqepy0rw; d;*50xrep e 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/ kadyu+n5t 4hsh9-nh o n8re6 thin atmosphere of a planet where the speed of sound is only o4 8urkdh/ny6nsh5-htan 9+e about 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s strikes the ocean. Determine1m4, xkrfrvrth yd..fg- wm mq4h*3; n the shock wave angle i rf ,trwxdm;.r4g*kh34. q-mv 1hnfmyt 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 dtzb/; 2y (nax$/theta$ 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. oz/yo:poeefq )u+ c9ubn*d* km above the ground flying faster than the speed of sound. By the time yo p/.neufo dy oe):9q*obc+u*z u 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; i3ba rob-u9dmh e)7rp/7; lyp bekn--Hz sound pulses downward from the bottom of the boat, and then detects echoes. If -3m7)nu /b9d i pepb bholk;7;eryr a-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 ranbm ypoq ..acphv5r:1*ge? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called(gdl1oqe7 a fe)srq y .bo5u-9 a sewer pipe symphony. It consists of many plastic pipes of various lengths, which are qf1y uod7aesgeq9-obrl) .5( 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 ay 0 me1yul0pr*- sb92q;yfj0h / s+hfvpccfm2 sound close to the threshold of human hearing (0 dB). What will be thesfp f2ym ;hyvbfu 90m 1+h 02 lcj-yqsp0ec/r* sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when anjxaupb(v/jrm w 7 ;h21 82-dB sound and an 87-dB sound are heard simultaneously? 7mjp/b uva(;hr1wx2j   dB

  The sound level 12.0 m from a low2wp/gvni .z:x/nr,b y7ojp / udspeaker, placed in the open, is 105 dB. What is the acoz/ pnyrxwwg7/:ibv/ p2 no ,.justic power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 100s yysk-0meu9qb.- pkyf8 m9t00 Hz. The power output drops by 10 dB at 15 y me 0k .fu-yk0pstqs mb-9y89kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over tydw tr e(2u4l.7 -atqyheir 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 radu y4wtdat.ye7l2( -rqius 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, t hzlob( 61x3ophe 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 is tuned to a f+wq9i-7u*s 8+be4eqhpuemc pfy3 tfxq 0 . d.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 q* xijuw;,,osa*k7e /9khzg :p rli,i32 cm long between fixed points with a fundamental frequenc9iu,kilgq 7r;ak * iz/jwo h:xes,,*py of 440 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 in;k;*e3nws yas:0b+en-mryf w to vibration above a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly.ar;0ys kw+bsn*mef-3yew ;n : 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 w4lnt 2phtc93 that is open at one end and also 75 cmlp2c4th 9w n3t 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 observed to2 cz 4tek4 1wfc e;kq4t(nd6uz 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 purtav inco:62sg k:)07ykfj, p se tone in the 500–1000-Hz range coming from two sources. The sound is loudest at points equidip)a:vi oj7 0y:ks n2 tgk6,fcsstant 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 whistles. One traf2qxi r hsk*s; o36hg4in is stationary. The conductor on the stationar *6 2ho3x kg4;fsirhqsy train hears a 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 whistle as it approaches you is 5q l4r4lp +)vil pl-jsxjeue7k6r3 5t838 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train movire6j8llk3 75q l4uxter -)+pvlpsj 4ing (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of c cxc8*;a cea/3f2af8 awwmkt0 ars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose ax 8ak a*0cfcwwmec2/;3 at8fthe 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 togeth r:nwq m+bnr1g;+ztx-,ex2m+r ij+ lwer, produce a beat frequency of 11 Hz. The shorter one is 2.40 m long. How long is th :r2n1;rw ln wjm,tx -+mibz+qe+g+xre other?    m

Two loudspeakers are at4 9t/n* x :uwjrqkgl2k opposite ends of a railroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listen9njk24qwr /:kt*xugl s 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 nkpr24y 2dxu-yormally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflecteyry2k-p2d 4u xd 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 9m8j du8ttw7pog 7e;cqz/e 5fwhile 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/d7u5jecz 788po eqtgfmw t9; bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound pulses as it approa;usj -kt f;dm5ches a moth. The pulses are approximately 70.0 ms apart, and each is aboj;utk d;-m fs5ut 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 one Av9 r boei:3dpi9qh4 4rimp 4*clpine 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 ri ib43qph rc*p994 div4me:othe 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 compromisrurb14r b c,g*)g *rhued by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nod*)rr 1,gr rcg*bb4 huues. 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 w a3bxvr9 ;-emhlm h+/rods,” involves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, loud, ringing sound. For a 9r+xha-/wl;3ehmv b 9m0-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 - t; lm.v-xcn6ovwpv u5/lwh- at a frequency of about 1000 hvo tv5./n -mcuw6p vll;--xw 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 Mazf b)p dcn85cv)1 k;xsch 2.0. An observer on the ground hears the sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s altitude ;px))c8zfcnb15kv d s?    $ \times10^{4 }$ m

  The wake of a speedboat isff:vwp;jjmyr e y+ *-0 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