What is the evidence that sound travels as ars+ocl x:atgk *7o .myvg r/+6na1,gs wave?

What is the evidence that sound is a form of energy?wkcf9hi e6o97zoa 8b zf:wjsm/en, )yn8 n s07

Children sometimes play with a homemade “telephone” by attaching d1im* a r xf8:h9ft9l ,cdn3kxa string to the ,fk3 h9ldcmft d:98r *inaxx1bottoms 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). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into wategzai8inp q;vq c;bcp.:8 np4:r, do you expect the frequency or wav pqipn;zn 88a :icbqgv:;4cp. elength to change?

What evidence can you ycz9ml9 zg7* zjt9(vo41 kw vlgive that the speed of sound in air does not depend significal4lg 9zy9wc z17kv o tvj*m9(zntly on frequency?

The voice of a person who has inhali4yg0 ,zi v2h.tktw8a;d d x3bed helium sounds very high-pitched. Why?

How will the air temperature in a room affect the 6q vji ry6nl pagcr7+ld7 *+v0pitch of organ pipes?

Explain how a tube might be used as a filter to red4 kppxvw 59cbuqo9g9*uce the amplitude of sounds in various frequency rp9g u9xwcpv5*4 okb9 qanges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) sot-u b-)cl( y z*;bpwtpaced closer together as you move up the fingerboard toward the bc *o-p )ztyu t(wbb;l-ridge?

A noisy truck approaches you from 2 fg0r1n h2cwibehind a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is sudde21ri 0fw2cnhgnly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whe/z7 grs1kwd o3reas beats can be said to be due to “interference in t g1wkrds3 z7/oime.” Explain.

In Fig. 12–16, if the frequency of the speakers were loww4fxzzq7ly*.q-mvo k l- u9 2wered, would the points D and C (where destructive and constructive interference occur) move farther apart o9lm-qzz * -uql24x.w koyfvw7r closer together?

Traditional methods of protecting the hearing of people who wox) 7jhirrx28stt*3v8gv) o wv rk in areas with ve)txo vs 8rv*2i7)8 tx3vrgwj hry 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 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 wavey0fw67rs 9vir22jied8ako*u can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two v2jdof08k *uyr wa 769eiir s2component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and tbz2olgq(d o/64 o)q q:d2zca d5 xe,sobserver move in the same direction, with the same velocity? q6) bdqqat( /dsg2,e xdoz2o4o:c5 zlExplain.

If a wind is blowing, wil4; grh9 frh5fwl this alter the frequency of the sound heard by a person at rest with respect toh4rr f9;5w fgh the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positiona lg;u8( m*adls of a child in motion on a swing. A monitor is blowing a whistle in f ml*;dg8l(u aaront 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 for the echo ofo :/ey2es apfn591psit -dcd / her shout reflected by a cliff at the-ay/sc29oet p:1s5 nddie pf/ 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 waterline. He hears p*u.fws8 . biqh7:sodthe echo of the sound reflected from the ocean floor directly below 2i :8u qsd7who* s..pfb.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 wave0di eq yn3asygu,/.7q lengths 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 jusq, h p78 t jyhxwdj 22j-+yz)hjp1v*0-zkagt kt above a school of tuna on a foggy day. Without warni yvz+kz jjy*a7hp0h, 8qw-)tp j hj d2t21xg-kng, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The swhohxq.e:ogp 1 2.ow, plash it makes when striking the water below is heard 3.5 s later. :.o1ooh p2hwe x.gwq,How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone striknk e .,ujj1os9z.o*nde the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away 9sod onn e*z.j1j. ,ukdid the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made ovnyuf-xlz4+ tz4xt,jek)4* y je n;,cqer one mile of distance by the “5-second rule” for estimating the distancfq4je cj,yztu x*z,y-4 e t4)k;nl+nx e from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain x gmb98i2peo; y w(-utlevel 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 ne:d/ (4ket1ol2r;( aad:l 2y apsntfwhose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simul.*v2eni,js y,shgq *itaneously at a certain place, what will be th hv2 ys,*,es*n.j iqgie sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane w/4fo+6uv ff m.*iwjhaith 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 mjvhf.f/ 6f4aw+u*oi shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas for pi-8eff6yu4z ,w wb3 fg4p6hma CD player it is 95 dB. What is the ratio of intensities of thf zh46yp fpwm3ib ,4f8uwg6 -ee signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound frokb jtlv74 m v:9xm3o:yq)2e0n6dnky om a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centerkdtj67mmble:24v ynoq 9v k0 o:)n xy3ed 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 whose area is7*t/6dw ) i7cm muijiyyf3gp /5vy,gf $5 \times10^{ -5} m^2$ (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 thewozvi/tf8ad7 s uf*iygoqx1 ,h2 y6,- more modest amplifier B is rated at 40 W. (a) Estimate the sound le62aq x1gyth,,sd-7/*yw izfvifo o u8vel in 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 dB when placed 2.8 m in front of,3 bs/9 he j2b5magjhl a loudspea, 5m ha/ej2sg9blbj h3ker on the stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound level of 2.0 dB. Wh50fk ssi6q j9vzm*)mw1 a:jwa)ppo+ yat is the ratio of the amplitudes of two so o)pj16 j w*ivywqa+ 5m)9 0kszfpsm:aunds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the ie6h1f5i(f+:gur6lsel+z d y m)k l 6buntensity (6gf16+l5 sldlyi 6e: e z+rh)ukbfum 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 has twice thei3jaub4 /77qc otr )veule5dw t;c4;x frequency of the other. What is the ratio od iuu 7c) 5etvrexo44ajt;7w/b c; 3lqf their intensities?   

  What would be the sound level (in dB) of a sound wa-p; 1f r5 : /za(rar.hhfgi1 cxyux:vxve in air that corresponds to a displacement amplitude of i5.fv:prcf 1hhx/;yxgrauxar -(z:1vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must hay, lyev1qd721 metju0,oo w8hve what sound level to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig.1y2 e7 hdv0,o,8uy1ewlotmjq 12–6.)    dB

What are the lowest and highest frequenciesd ;u:ul ylgu*+eba7 i9 that an ear can detect when the sound level is 30 dB? (See Fig. 12–6.:y7eu 9b*gudi l+lau;)

  Your auditory system can accommodate a huge1w sc+gd hu65lfs 68n2)vp 6feejn9no range of sound levels. What is the ratio of highest to lowest inv p86n9n2df6hc5wog 16lfsns +e)j eu tensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has d;ca(rel :0 ly m4hs1fa fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass o(4: fsah m 1lcer;ly0df 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What pbgj*ei8 eh-3 are the fundamental and first three audible overtonesgjh3p -ieb8e* 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 expecpjpc)b tl 21a)t from blowing across the top of an empty soda bottle that is 18 cm deep, if you appat c2bj)1 )lssumed 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 witnu3t.yxm-o)d e 23uuwa0h8j xh open-tube pipes spanning the range of human ndom2.- 0ehwxyj3 ut u8au)3xhearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string hamc6fmi6owy1 z t+rz9-s a frequency of 540 Hz as its third harmonic. What will be its ft cr-of 9wy+66z m1mizundamental frequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to 0:w242ilujfotlx 8a lplay E above middle C (8l:a2lwoj20ul itf 4 x330 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 b2m6 uknkd.+ps x)2rpxjp m,* an open organ pipe that emits middle C (262 Hz) when the tmjk*r. b2)pd2,u+k x s 6pnmpxemperature 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 dpl. nm.9dsmr( vn56q8yo a s020 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiec)ljk.gkbf-jx 9m rk50e of the flute in Example 12–10 should the hole be that must be uncovererk0b.k x5k 9fg )-jlmjd to play D above middle C at 294 Hz?    m

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

  A particular organ pipe can resonate at 264 Hz, 44 0yz z.)jk-.cch4fv pf0 Hz, and 616 Hz, but not at any other frf)jyh .k4c0- .pfvczz equencies 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 h uoob 8n5cmk v-/lgxk8a+k0,both ends. It resonates at two successive harmonics of frequencies 275 Hz v5n,8 kho-o0/kg8bal+ mukx cand 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 qxejcn-e8c-e ,a0o4y $^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are present within the audible range7/jxe+s r8hh87v ogx8a+4b. o aksanl for a 2.14-m-long organ pipe a+.8/+va 4asn7oxlbho7s8xg8hjr ke a t 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. c 8cx8: --t/tv pmnvucIt is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the a:c-8c/v vu c x-ttpmn8udible range) of the standing waves in the ear canal. What is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to 5wzoin*j:dt4q s gd*e tfmv: 1-/su;eadjust two strings, one of which is sounding 440 Hz. How far off in frequency is the oth mug:4ofwez/eq;-int: *vd1t djs5s *er string? ±    Hz

  What is the beat frequency iw n i3n: w g+zvv;a/ug467ef xtge.ud)f middle C (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while anothp(mnl. . td0ymo3 v2f+3l gqyver (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 .+pgv ytvqn.(f 2md 30lmlyo3 are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/.x p, xvt,gh+vs when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning f , .g,vh+xxptvork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings ar0im kx+1.xzzg e tuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hintikg0+x zz1mx .: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play middle C (. a7.ppf9myok qb7 zu q5h3*sh262 Hz), but one 97qbp3 us7.y.m a5phfz k*h qois at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A,fb)q ltpn i5a28u t0+n 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 frequencies of A and C? What beat fu5n)+qiatnbpl f280 trequencies 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 from one speaker yx0mhnt -t;oo5z 3t ehcn/8* wand 3.50 m from the other. 3e*8-t th0/n xytzo nh5 c;wom
(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 suppog18j)lajdu7tlej7j fz4zpm z p64z:5sed to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what ml)j a8z546mppejf4j zglt1 zz77 :ju dust be the frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound of wavelengths 2.ux., vxw9/bnt 6p)l 2t2w ldum64 m and 2.76 m in air. How many beats per second will be hear wpl26 )w.ubm9dvtux l/nxt,2d? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s sirenq3.9-lv d*ggpz ma9v g is 1550 Hz when at rest. What frequency do you detect if you move with a s*q.vz ggg- padm3v9l9peed 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 whov a8 :,n.fe:u.cztln4zy sel(ru 4 +hese siren nv4tl . z:lyfu8ce arh+e:n(.e,zsu4 emits at 1550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 20q0ux 9dcfg+ l400-Hz source is moving toward you at 15 m/s versus you f40 xgdc9 luq+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 fre -qxw:.g:g xzzg/ux2ycue6sy j0)/a r quency 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 freqz):yx r. gwcx/:qu a-/g2zsyjxue60 guency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends outy nv)zm1d ajvu 9l9+zsg3)1 pw ultrasonic sound waves at 50.0 kHz and receives them returned from an 3 )+j py sdmvu1lvz19zgwa)9nobject moving directly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As i xpd2 ;4/qu-ghegjdz ;t flies, the bat emits an ultrasonic sound wave with frequency 30.0 x ;dd p2jg4eguq/;-zh kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experimegp zx8x.ax0i )..vg 3 qoxy*bcnts, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a secony8*x x.3b.av c0pxioxg.)gzq d 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-flow speiu m+s()2 jnnjeds. Suppose the demn(j )j+ is2nuvice 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 source?   Hz

  The Doppler effect using ultrasonic waveskcz c m9x87dd0;dy: rc of frequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequency 570 Hz. Whe0bd/nml b/d 45mjj:pfn the wind velocity is 12 m/s from the north, what frequency will observers hear who are located, at rnfbd/dm: bj l/0p4 5mjest,
(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 f:jflx nb.z vb *+v9:pvutc6+ 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 sr(*ru1btrg d1z;w ; a*hwse-ba3d 8gpound is 310 m/s (a) What is the angle the d;*ut zr8g* ;h(1wdsr3-rag1b be apw shock wave makes with the direction of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmosjjnq/ vs6vssbwei).,rb 6qy k.+o5u. phere of a planet where the speed of sound is only abou.sqju ibv5onwqs/ )yr,. b+e6.j6ksv t 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 str11phcdvto 1v*.m7e.z 0en ln(1co kf xikes the ocean. Determine the shock wave angle it prnzof701evv1om e d1(n*x c1 clp.tk.hoduces
(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 sp1i,v y ,c+x- s;h bo3xprqc .d/iqug58osu($/theta$ 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 ground f v+e(r-zbmva7d n;b (50qcuxllying faster than the speed of sound. By the time you hear the sonic boom, cl(bx-veq(vu;a+dbr5 0zn m 7the 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 ams-awo-; vlf* sonar device that sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed -lf-v saom;w* to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are e 5zjw5y2p+fothere in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It ;yluxga2o3*ii9u*im 5fo x 0m consists of many plastic pipes of various lengta0 xu5i3ofxii*m*9 g ;m2olyuhs, which are open on both ends.
(a) If the pipes have lengths of 3.0 m, 2.5 m, 2.0 m, 1.5 m and 1.0 m, what frequencies will be heard by a visitor’s ear placed near the ends of the pipes?
$f_{3.0}$ =    Hz
$f_{2.5}$ =    Hz
$f_{2.0}$ =    Hz
$f_{1.5}$ $\approx$    Hz (Round to the nearest integer)
$f_{1.0}$ $\approx$    Hz (Round to the nearest integer)
(b) Why does this display work better on a noisy day than on a quiet day?

  A single mosquito 5.0 m from a person makes a sound close to the threshold of hfj,a fq-a+9 maumana +fmj,q9a a-f hearing (0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an i k+) +hmwvyn887-dB sound are heard simultaneo+kn mwyi+8 )vhusly?    dB

  The sound level 12.0 m from a loudspeaker, placed in the ope(x:9 oh 0f:yekpn /wecn, is 105 dB. What i::e0opkcfe hw( y9 nx/s the acoustic power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The l 7idxcf/g4qdf6h )l6power output drops by 10 dB at d/ihl4 c6q)fg76 xlfd15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aj, s.yu6 1kzzvircraft typically wear protective devices over their ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be thezk vj6,zu1 ys. power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communicatiofo*ohew*q 9/ ons 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 fr(, ;seo+v u 9jahmz;zgb; y,rwequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long between fixed wy,dijfij ol 2yve39*k *6lt7 points with a fundamental frequency o96t fyiydokwel23, *ij l 7*vjf 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 vibration a x)xwk8 v*4jcwbove 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 thxcwj k8 v*4x)we 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 y5vi5 +p6cuug at one end and also 75u+p6g5ucy5 i v cm long. How much tension should be in the string if it is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was ob:w)hhj)7eja yj 1j 8ci87mwnaserved to resonate as one full loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz range coming from two sourcepb,pp v.pxh60s. The 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 lev0pb6 pv,pp.xhel 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-Hzwl4q3 ybs1 g2 ,gnncl6 whistles. One train is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of q6c431 lbl yswg2g,nn the moving train?   m/s

  The frequency of a steam train z,x -b,ua,fwewhistle as it approaches you is 538 Hz. After it passes you, its frequency is ,z-xaw bf,ue,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 by listening to the difa4,qn3c+1 mamogr/1g g5qw rs ference in pitch of the engine noise between approaching and recedins +4qcnarm/ m3 , wog1ag1rq5gg cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 1e 5ns9zb.)qw,b 8kfqm5j byq31 Hz. The shorter one is 2.40 m long. Hobmqjb)swq 5f b9 qzk.y5 8ne3,w long is the other?    m

Two loudspeakers are at opposite ends of a railroad qi,ts:yrl +5+ ioa 6i*p)ws rqcar as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observer when (a) he listens from the position A, in front of the car, (b) he is between the speakers, at B, and (c) he hears the speakers after they have passed him, at Cp,ilq+qao*i 6:tsr5 y+) wsi r?

  If the velocity of blood flow in the aorta is normallyvjx( y a/qm7*jzd3/dke*fxl:ng* ji- about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasoun/ *fxlz jm3:-n*a7 *gjky(x v qijded/d waves were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s while u md od 7 13p6ja,-v1asdsry s1j7f;hcthe 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 thj jr 3v -,6s1hdcdaaumo71psy1;7sdfe bat after that wave reflects off the moth?    kHz

  A bat emits a seriesp8 vz3lyva(j1 2 ry3xo of high frequency 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 awayr v33pjv lx1 y(o2z8ya 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 Al2xjzwj 9r skpm ;8ry:6u)u4cgpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called tc 2 prs4m)w8 u6jr:; kgjuzxy9he 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 standirok*jgsk kjaj 2u5 //:ng waves, which can cause acoustic “dead spots” at the locations of thj :ojksk/jk u2/5g*r ae 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,prt03lc4kjgcg9 / :x i” involves a long, slender aluminum rod held inck4 jc0tig glx 9p3r/: the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the threshold ol2nz 0*mylt.mf hearing for the human ear at a frequency of abz *tl.2nlm 0ymout 1000 Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on the grounzyqpz v. he1+0d hears the sonic boom 1.5 vyhe0 +qz 1.pzmin after the plane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat )ts d kkzp8xce5rg(+;is 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