What is the evidence that sound travels as a w:q88febkm2pivf z 6ak i2gugdl08nn7+h h0 :wave?

What is the evidence that soundp0dt-bf/1cditvx* m hh:)8 zb is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a string to 9 0dhc8cp,i zkxsp3m 0(ibi,qthe 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 k h9xc iq(pi p8bsz00,c3dmi,(Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave pass4,lgjo )ff tj4df/k) fes from air into water, do you expect the frequency or wavelength tfl,4)jj4f f fogd k)t/o change?

What evidence can you gig75of(vh7s;8jlzy2uh k.nf- bbwn , mve that the speed of sound in air does not depend significantly on frequencyh s5uz7g,ffyn2mnv8; (bjk.- l7 bhow?

The voice of a person who has inhaled helium sounds verrc9u 0k0mdz2 jv)qks4y high-pitched. Why?

How will the air temperatu(uty(13orc aire in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the ampl , b3+rcxqajninog7 ,x*ni3 x7itude of sounds inbi +r7igxo a*,3 ,37nxqnxj cn various frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar *1 kl)u bz k7elh,r2mh(Fig. 12–30) spaced closer together as you move up the fingerboard toward *)h khbz12kru l ,elm7the bridge?

A noisy truck approaches you from behind a building. Initially you heay 5guchw)6ty+ q09c rtr it but cannot see it. When yc0)5+yt w6 q9hrtcgu it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due mp xi8sz )0xd1to “interference in space,” whereas beats can xp)xd1z8i 0smbe said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, wouldzp n;r2;ev/f7jap 9fe the points D and C (where destructive/jzp vfn;9a7p re f;2e and constructive interference occur) move farther apart or closer together?

Traditional methods of proted+ g)jyq,c)kscting the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it d+gqj,sc)ky) 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 i czr sd75(isv/v:u.a on Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (7:a szdv5c.(vui r/sob), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if t n acpo-13/o4 /iscgfqfb; 2iz9c,ylqhe source and observer move in the same direction, with the same veloc 2yic f/gb/c3ocqfl 9q1-z i,s;op4an ity? Explain.

If a wind is blowing, will this a wf 0b zae/j4wp,w)h)wlter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or v wa))w0fpjww4z hb,e/ elocity changed?

Figure 12–32 shows various positiof+fr9kpw 6i7ieau *y-ns of a child in motion on a 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 fi i6kwf-e ruyaf*7+9p requency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening f46 8grulg 0dcwic co.ydgrg nt721.y+ or the echo of her shout refleclyr.g w 6+iugddrtc8g 7yc210oc.g n4ted 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. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterl )wqc4d+s.tn tine. 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 do tt)ws4cnd.q+ es not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air at 20 *3 bxm*m(zfsh$^{\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 of tuna on a foggy day. W c3afu+5mtboqc,qi 416 uzgq6ithout warning, an engine backfire occurs on anothe5+4 1 36i6ta,coq zb cmququgfr 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 fra,;nm uamfg-)k:stv1sqop 8 )om the top of a cliff. The splash it makes when striking the water below is heard 3.5 s later. How high is;ft8:)v-q)umaampgsk, o 1 n s the cliff?    m

  A person, with his ear to the ground, sees a huge stonehst;0z-vo;2wk7q.yi nayn ,gxx(5 pq strike the concrete pavement. A moment later tw-n5pnqiazx ;h7 ;v(,y o2x . sg0kyqtwo sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error mademsuo68m1w2+uf *) o n5hc rtqx over one mile of distance by the “5-second rule” for estimating the distance from a lightning 5tm)hu mw* 6 +q12 cuxf8nroosstrike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a soun+k rzrr*l/ )idd 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 in/tz2gja ql4mr i4 e;c/tensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneouf t9oo1(qz 1kg23o x7oc:x 71ymiachcsly at a certain place, what will be the sound level if only one oax:tcoyic g3h7o2 f11c79k q1mo(xz is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a cer f-98oobs)ni atain distance from an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB.98 )-aobnoisf 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 signal-to-noise rax+ n 5gb7oi,r fiz(0datio of 58 dB, whereas for a CD player it is 95 dB. What is nx r(0i,5 gozdi7+bafthe ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power rxwdo b*ykq 0p/ c6 )dy(sv3:qoutput of sound from a person speaking in normal conversation. Use Table 12–2. Assume the souq (*sy) w0kq6vxd r do:yp3b/cnd 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 an eardrum whoseesdn/;6y1 o49a)ys: tzy:;wefujr z j /hm ph9 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, whildtphnz9qy++d l1 x-pwwbf5 00e the more modest amplifier B is rated at 40 W. (a) Estimate the sound level i+1qzn- b dxl h5t0dfp0pw yw+9n decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registered 130 dBe-o2nllm d d9ud, rj2, when placed 2.8 m in front of a loudspeaker on the st,e9d2r mlddlj n u,o-2age.
(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 ode9 sr7mvs96qyc9ow z k.u6 5sf 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels diffvy6mku97o5sw9 z.qr9scd 6 s eer by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what facto( ;.8htyy6d kuk ls0aqr will the intensity increase? Increase by a factok(. l6;d0qykthu8aysr of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has u4c9iw,*ynjhu a s0; ztwice the frequency of the otheru s 0cwi n4z,;9ujahy*. What is the ratio of their intensities?   

  What would be the sound level (inpgj48 w5mvf dtchon3m*1- /sh dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz? 5fm 1sh4-woc3 tmdp jh/vn8* g   dB

  A 6000-Hz tone must have what sound level to seemkgh 3n8wo5c1zz2n.wi as loud as a 100-Hz tone that has a 55kin.zc8wz2 w1no g3h 0-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detec,;b6/skf jpx kh/jhz5t when the sound level is/bk/ xsj ,5fkz6phh;j 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is th13cwmrybgco8m(u h t93 oey+n+r.1pze ratio of highest m8w9o3bo m+1y(3gerrhyc1 nct+zp . u 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. Tvfcee)s ,u1d 5ci0 ii7he length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tes e1ecid,5uc i07f)i vnsion must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and fir7 0uxn. uc-ldbrqb.x4 st three audible overtonru b4 .cx7q. -0ludxnbes 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 from blowing across the x:6 bl*z sis+ktop of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tube?sbk:iz *6 sxl+    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-pigfvyrz v*5 lc/; i7 ww4pn+4tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would fn7w*+zc iw4v i /4rp yg;lpv5be 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 y/qfk7ypa de+4vn98(u h* 3p dogvw,xs third harmonic. What will be its fundamental frequency ify9pw vo8dfq/4x (3*ka dveyphgn + ,7u it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E above midd z/fwk;/b n3kvle C (330 Hz). f vz/ /w3k;nkb
(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 tihskuh /286j iomg/0open organ pipe that emits middle C (262 Hz) when the tih 2k8tsmju/h6/ iog0emperature 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 2mi (;eylgs6 p,w*,vy h0 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flutuf*ok.-nqt/w7 gt:hzkdy a/ 3e in Example 12–10 should the hole be that must be uncovered to play D above middle yk* ko3zt a-: gnu7 f/d.qht/wC 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 no-2(w5 fu 4gcnt ce.tj;83ailews7vrdt at any other frequed3ttgve i 5rwjs(lufa4w.27; -encc8ncies 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 resu0g+:8d2qf u zw.smva onates at two successiv8.0w2sfg zmud:qu+a ve 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 gvj5)y dzj3 97s vpo9dwt.bv/ $^{\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 pre nq) .47)oejqk0 qrd gtps/vs8sent within the audible range for a 2.14-m-long organ pipe n7)8pjgqs0srvk 4q e)t/d qo.at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximiex 0r7d(g4x hately 2.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimad74r h(egx i0xte the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s brg a2pm t7v6m bi35,uwhen trying to adjust two strings, one of which is sounding 440 Hz. How far off in freque bt ba72r,um6m3p5 vigncy is the other string? ±    Hz

  What is the beat freqg0w8e / . xp0;ydvipx0iaz7g buency if middle C (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, whi pa1s4 +6,m 6ukwjbivule another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans 64+ svpj1buu6ai,mwk when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork andz* .7 * 6trgzmdcobfv0 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the stringbm* rgz tf7czvo*0.6d? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, xmw mx.m:4cx(294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall xw(mm:.4cm xx Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes ,m*11jz u0 npv, d+k8qvhklxheach try to play middle C (262 Hz), but one is at 5.0°C and the, 0lduzkv jnmkhv1 ,ph*x1+q 8 other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks dscw9 j0w9 ynv0m3a4cbmj6h3 , A, B, and C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequenciesj3943m9jmh bdc ywvc0nsa6 w 0 of A and C? What beat frequencies are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A person stands 3.00 m ftlwmzw60t4c /0 ghy3 grom one speaker and 3.50 m f0/ twty gz3mhc064lwgrom 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 be4sn i csb9 z9wpq+wq/4 vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are plapqq/ +s949 iwb4swzn cyed 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 wavelengths 2uuu75 b+1sirz .64 m and 2.76 m in air. How many beats per second will be heari5 7 1u+brzsuud? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a cer qb zg.8z+9udgub6b kvsm;y//q )gw*rtain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move witmqv/;.*bbwzq d gbu+sgzy)k/u8 gr 69h a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a fire engine whose sirekqd -uj24-yfd0j5p h kmfbj1 2n emits at 1550 Hz moves at a speed of 3yd0k4j2 hbdm j-qjf 1f-p2u 5k2 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift ,rt) yrp2c* fhin frequency if a 2000-Hz source is moving toward you at 15 m/s versus) fhy *,ptrcr2 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 equ p qpt/ht3e,8 vhy*4bqipped with the same single frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency tttp3ebqvqh4 h*y /,p8 he horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receives 02/ cny+7e2itsvq9hw, 5tf h3sna zrb them returned from an object moving directly away from it at 25 n /h27n,wfats+tcqybsrz ei hv 50329m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5nv ,y: rztq2v4 m/s As it flies, the bat emits an ultr,r2ztvnq y v:4asonic 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 tubt:/jle-o klq0a was played on a moving flat train car at a j q /olktle0:-frequency of 75 Hz, and a second identical tuba played the same tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-asx 44rl+g v o2o0a5kaflow 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 bl0a4s oaro5g vlxk4+2aood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrau)(x lc7ma+me wj6tmn*qu ;xj ,pb b:*sonic waves of frequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequencyb;sfdn tm7 ) 9./ fw8qetdkpnucx *-w* 570 Hz. When the wind velocity is 12 m/s from the north, what w.9u 7* nfd8t)-dbqp*;sencmwkfx/t 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 moving on land if its speed at 2n4c:a-ah .wjg0 $^{\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 isq 58/:o;lx:bqhqqe bg 310 m/s (a) What is the angle the shock wave makes with the direction of the airboeb l 5q/g:q;qhq8:x plane’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 at *ty p2kfxfc*4jv1b)9x -peth mosphere of a planet where the speed of sound is only about 35v*t fp b-jy29 ft hxk1px4e)c* 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. Determine51t uymh n;3ri the shock wave angle 5t1;nhu 3rymi it 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 lv5zn;l t4u 994 mywbh$/theta$ 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 exachqmj 9f,5 hv+0ulcycg74.f sztly 1.5 km above the ground flying faster th 7hs,h l z.gv c9yc4mf5uj0fq+an the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 12–34. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device t/yqsii6 lkvs qf 3, qm(5c3qz e9r9(nehat sends 20,000-Hz sound pulses downward from the bottom of th/i(f q3 zv,qs 9qr36csi5q9 (nmyleke e boat, 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 octhb1m 4m56 ur-1gjmmd/ kev2o+h /7r0chk h rpkaves are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a 7a0ap6 eeszw( display called a sewer pipe symphony. It consists of many plastic pipes of various lengths, which are(0epas6zaw 7e 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 o4y) q2oevks1rn+gtsf(qko3 t;j.w0 1bl.hqa sound close to the threshold of human hearing (0 dB). What will be the sonfgh(v1st l+qwkoy24.)boq.; ekj0otr3q1 s und level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-dB so7 vgqzv6 dt:)fund are heard siz:6g7f )q vdvtmultaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 1+ bd ezpr3+t5i05 dB. What is the acoustic power output (W) of the speaker, assuming it radiates equally in all directions? z + b3tr+5iedp   W

  A stereo amplifier is rated at 150 W output at 1000 H w ht)o*ip8n (vg.3enu9tdm t*z. The power output drops by 10 dB at 15 kHz. dg9 t(o*u)htmt *vi. 3 wpenn8What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices o;,j5n5mhoad:tgq ;n*lo vtsa8pq i 69ver 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. m atj55:i ;86n;nt9,a qv lqop*ghsodWhat would be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communica xbac7 .d*c/xstions 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 is tuned to a frequency 1.ds*n6lsof et p) 3q;nzw +l8h$\frac{1}{2}$ 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 lonxd:zgom kn5 -is + ,-,equt3xag between fixed points with a fundamental frequency oxunka, -oz + ime- s,:tgd53xqf 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 into vibi1d4);l2 bylzn *+h ci cfib5yt6v ui*ration above a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.392 *iv ib+d 4 fhnt6;5by1uci)l*c zliy5 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of mass 2.1m0b+g.ftb2/ o;v.nzlns8 txd 0 g is near a tube that is open at one end and also 75 cm lonxb 2 +/g n.l;tdfnmv8s0.botzg. 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 to resonate as onz6owwyk6uw t)fgh c*uoe8 80*e 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 sources. Thfg.dz/hr+ +cge sound is loudest at points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than thfdg.chr/z+ g +e other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. bap.+npgoh, 5One train is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequency whenngbh p+ po5.,a the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam trau98o0d 9iceu. /iyyh kin whistle as it approaches you is 538 Hz. After it pa di/ o0iycey 989hu.uksses you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars just byc9wq2ikopy*1 t4a(p k 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 (fre29i41c qwk * apkyp(otquency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce t0jtjn-j4. jc a beat frequency of 11 Hz. The shorter jt cjt j.jn-04one is 2.40 m long. How long is the other?    m

Two loudspeakers are at / kw+t r7o.leyopposite 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 sotw+ky/ l7ro .eund 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 about 0.32 m/, wpy), svtr7cs what beat frequency would you expect if 5.5wty, rp)c,v 7s0-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 moth4-h tmm4esy/( tdv+j 6f*w4jzrx-ko s at speed 6.5 m/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 themoy4 /w jr-tv*smfe64s+ d(k ht-x4zj wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound n.93h q( jsxfgpulses 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 t3x9j qgh(.s nfhe 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 seja1/8 ;c.mp wt: phro;xo1h xend signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, lon/1axxoh.c p1wh :;t ero;j8 pmg 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 an open tube.

  Room acoustics for stereo listening co (jnf9kwqcyo5 dm3 j+/*r/3gxx5 kt lan be compromised by the presence of standing waves, which can cause acou5/*xojfmwd39 jtxk 3 +qkco5r g(y/lnstic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamental frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, slends8f 8u,jk*x*l(qun bder 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 “siqjx*(b k*8ufu8l ,sndng,” 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 (gi*qc u9dlbg8 u8tl7 for the human ear at a frequency of about 1000 Hzibg8q8 9tcudu7*llg( is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on tcwx cq1.uqo: 9he ground hears the sonic boom 1.5 min after the plane passes directly overheadw:cx oqc.uq9 1. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat 6vmh:m2l: ceeis 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