What is the evidence that sound t:rs .un vx 2pwm7e;rbj4+ee8lravels as a wave?

What is the evidence that soj : 1z7 wpw*(/ef oe3+ydyfbqmund is a form of energy?

Children sometimes play with a *z3ck j(vbz1zfc2fr )homemade “telephone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (F zkvb2 (jz3* rz)c1fcfig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passe8ow8d ndn ci61 avq9yv6no3 l9s from air into water, do you expect the frequency or wavelength to change?yv6o9 1v9wn8ci8l63nd oaqn d

What evidence can you give that the sp9ufgw r rpey+c 458na+vje- 4yah2 2ybeed of sound in air does not depend signifi+yev-caau r2ryhw2p4 y4b e598gfn+ jcantly on frequency?

The voice of a person who has inhaled he g3)) (x+iwtj tlqtwd,lium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of organ piji( a0cem+:i qpes?

Explain how a tube might beei*5tu 2x rc mxa1p,z/ used as a filter to reduce the amplitude of sounds in various frequenup*r x/tca21xm,eiz 5cy ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you move rcn j- f3uw:ftv,-ih6uptvj iw:r-,f n3f-6 cuh the fingerboard toward the bridge?

A noisy truck approache :j,+ns a8md8upsoda0ic (t1ls you from behind a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffm o al ds80(+:i8untc,jasd1praction.]

Standing waves can be said to :9u2-on:vjl a bx l8uxry.4tx be due to “interference in space,” whereas beats can be said to be due to “interferenc:u .a9lylv out-r8xjxn2 :b x4e in time.” Explain.

In Fig. 12–16, if the frequency of the speaq /fqjrnk:+ssa 9g f29kers were lowered, would the points D and C (where destructive and constructive interference occur) move farther apar fsg92a:9q/qnrj kfs+t or closer together?

Traditional methods of protecting the hearing of people k)wlt)t ,ja 26a *uvoqmpnq6 4who 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 to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levelq6k m,laa6 w2u)tjp4n)qtov* s reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thugq;e.xu8 v 6c7ao5t qought of as a superpositi;e 8 u q.v5q7ogxt6cauon 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 frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in the samj ptl7jz-ow c9+2x0e8be uo n5vnz 24ae direction, with the same velocity? nw2o ojbt4 579zp8ceu- vz2aelj 0n+ xExplain.

If a wind is blowing, will this alter the frequency of the snws , zw/v9lr:ound heard by a person at rest with respect to the so: wwv/,s9zlrn urce? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child inzf8 2 *wg*rldvn ax 0gqb9uj+. motion on a swing. A monitor is blowing a whistle in front of the ch *g *bzra f+jwqx8 0nvu9g.2ldild 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 leng j;by +t(a8wz1yqm.qpth of a lake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length +q; qy z1aym.bw 8p(jtof the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He hears the evghj nyl3e1yney39ns 9v j+6 1cho of the sound reflected from the ocean floor directly below 2.5evse9ljnyy3y116g+h jv 93nn s later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths inqj vq6pk.47,rvn3p)71qj l 8 mdlpl vn air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is drifting just above a school of tuna on a fq;e( ogcmu ,6e 3:3pgj0lk qtfoggy day. With3mu :q(l6qtpj0kgg3ec ; eo ,fout 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) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a c-t:9z bv oz0g jlfs7 qb-5cak6liff. The splash it makes when striking the water below is heard 3jqv -:a6cg9 ozs0b-flbz5 t7 k.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone str02q/mg soy i7eike 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 a0m2i/ 7es ygoqway did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile ofx:z1hhx9g sz- distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (g: xz-1z9hshxa) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound ayggw1l rtubk(4(gp 3 7t 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 ned68by( rhbms 4m w6qi1s* v;whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound z.5 nir, zjt-ails)u8 level of 95 dB when fired simultaneously at a certain place, what will be the)itl.i-sanuz z5jr , 8 sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certaxz6 h*df( ao3ain distance from an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but 6dxz*ah(aof 3one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to2*e3h en 3rpkl have a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the *23ep3r e hknlbackground noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from cj ey3zgo:hay, *q )q2a person speaking in normal conversation. Use Table 12–2. Ass ejoqzq3*ca2 )ygh:, yume 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 an eardrum wh:j9nhky t8um g,9f- qvose 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, whileg 4: y7r86 t rxe+u1(tu*eqcf gw-htue the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3e g7r(ty4 eufu g8w+6x rt:*-euth1cq.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 2.8n9w7wgniee(:cy : ; ejl,qb p+ m in front of a loudspeaker on the stagepnw :inbl+ ey,w9(:c7ej;qe g.
(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 detectz.uu fu77a ea1m r3qo(4bucrh 5h ot0. a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two soue u.cmu3.51z7 b04uar t(fhoouqh7a r nds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound njl6d m))8xf n,3xmxu wave is tripled, (a) by what factor will the intensity increase? Inc)8jdxnnmu , 3x 6lm)fxrease 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 twicm 5c. 9 usor(4jda6czkl 4ju,ogxl21s e the frequency of the other. What is the ratio of their intensitie odsszlcg19 ( 4 x,a5ruj6c .umo4klj2s?   

  What would be the sound level (in dB) of a soaau .5ka .n+lkund wave in air that corresponds to a displacement amplitude of vibrating air moleculka n.k+a5. luaes of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what s (p.q h5(uv0s /cnppmvound level to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig( (pv5p/ qnm.uvshpc0. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when the sor:b 2d5qg:z de mf0zytr 1b/t1a:w4deund leveldzb: z50qf:1 aetrr1 b2dt:/yedg 4 mw is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range oi 1 lnv(glqkob66t p:2odfbfj3kj535 f sound levels. What is the ratio of highestpgl(n b53 :l15tj 2qk6f3kjo fbdov6i 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 fundament.+u41 dev6to3 2)icy fcdlii g u/r/dval frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension musc6/tde lv+/dgidc i 3uf)o12. yriv4u t the string be placed?    N

  An organ pipe is 112 cm long. What are4-p lj* kj68. nizbpmn the fundamental and first three audible overtones izm n*k nj6lip-4jb8 .pf 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 frxzwqafu(k+. 9om blowing across the top of an emfxau+z. 9 wkq(pty soda bottle that is 18 cm deep, if you assumed it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with op8q.ia.5c dstg/iwni * en-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths i85. t.wgnc *diqai/s of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmonic)ey24 .dfk diy. What will be its fundamental frequency if it is fingered at a li4yk. deyf d2)ength of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long t1x97fy mlyd p87t h+kand is tuned to play E above middle C (330 Hd7mx 1 9k7y+lfyt ph8tz).
(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 pipe1dqacu8 m ygmtg2;dfl/.-(xr that emits middle C (262 Hz) when the temper 8mr g- m/yl f1d(ut.daqgc;2xature 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 ,6ghe3v/z 0q+0u 26jttju w mmnfti1eat 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Example 12–10 should the holkc2h(2+hz58)o mkfl .mwryap e be that must be uncovered toa).c( mkplyz 2h 2+k8mwrh of5 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, 440 Hz, and djy+vl x y-e6qob5plc.wkow1u2 b r by6+-)t4616 Hz, but not at any other frequencies in between. (a) Show why this is an open or a closed c -+y krobd+) y6uleq.tbw oy45jbv 6-xlw 2p1pipe. ----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 resonates at two succ7vk 0 lrambzgjrt36(-,q8e dcessive harmonics of frequencies 275 vb dt(8rezjck63,a l q7mg0r- 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 e9bj826iep3sfr (q kkh qz)8m$^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are present within the audible range for a 2.14-m-loch d /)o s5 tf3l*sar:czkb2vsos 1;z:ng organ pipe at 20 bo:r; o 1zzfh l s5s3/2dsst*va)c c:k$^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximatel c . br*xg1sntpe*8d2li4dwy7y 2.5 cm long. It is open to the outside and isyc8 g2npertw*lxid1 *. d 74bs 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 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 adjust tjy75. ;k xhoat0hbbc8wo strings, one of which is sounding 440 Hz. How far off in frequency is tho 0.ayjhbx ;tkb8 c57he other string? ±    Hz

  What is the beat frequency if middle C (262 Hz8a vmhsv8 i in;fzn;ij0ccw)m2;l1 s() 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+lr8l(ch u1 onrqk+ axxy-(, b at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine oxly-cq+ u(8, a(r+ o xrhkbln1f 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 fl9qhv3 f i)avt73r z,with a 350-Hz tuning fork and 9 beats/s when sounded with a 355- vi) lthf,397fqrvaz 3Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tenqs17 sr n u bqnr8obum-h:0i),sion in one string is then decreased by 2.0%. What will be hosq r8:n m -n)rui71 qu0,bsbthe beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play m njd5)jtkd.,.s5m dp ziddle C (262 Hz), but one is at 5.0°C and the othek 5d5.sdj.m ntdjzp,)r at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A,j0f7xb b9u7( suqs 6k1p + q:lpfe3cez 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 lp7 67(s9fep1 xqjcbk0fbqzs 3ue :+ uof 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 perk(/reew ei 09g5)hp rqr:xn 5gson stands 3.00 m from one speaker and 3.50 m from the other9igrnpqre)ge kr:xh/ w5e (05.
(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 9 x(iz3p tx:umlk+t9 1bl;.nx8rq.xzre9bxjsupposed 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 vi.1m lknt;q+ 9tu rjx.e bx b3xp:99(z x8zlirxbrating 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 2.64 m and 2.76 m in air. How many beats p,mfw1ep0:cn per second wilnmp 0:c1,epw fl be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s sir 9*t,d-xw2q5tmlfh 0a ;y zueeen is 1550 Hz when at rest. What frequency do you detect if you move m-lat* uxwh5ytze20,d; fe9qwith a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. W. m+ w2sb/iq:kbemb0 3jo)lmy hat frequency do you detect if a fire engine whose siren emits at 1550 Hz moves ye:i3m0 bkjos l2).qbwmb/+m at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequenc7s 3x9ngfhg8epfyv5+ y if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they x7f5n9sypeggf3vh 8+ 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 equipp,q d t u qflsex7o 686jz3vx1.uv3 fv)8o4dogjed 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 the horns evuug.3j3qo68vfdx4qf7s jlx, e)1zood 8vt 6mit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out e)k43; b dy*y j56jyha :0iqcnlkvci9g p(we;ultrasonic sound waves at 50.0 kHz and receives them returned frompc;n(y ely;ji)0gk9dic ah v6w5y:e 4j3qk*b an object moving directly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wal58j*v,c3vgz g* hafcml at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the rf*, v8 3c*zvhm5j ggcaeflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments,95ei7xejocjfv 0 w; trx3 47xs a tuba was played on a moving flat trr 54ewif 93vo tj7ec 7x;0jsxxain 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 approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasoundlhbtx,n(l-i7 qunpn2n e;2w- waves to measure blood-flow 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 flnh wt -72n,qbx-;2line( ulpnowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of frh 2h;1h5w4 (-ektc( qxaipmj/.c ict uequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequency 570 Hz. When the wind velocitydtoopo(1+gmuhc 1ug(m; ,ni 0 is 12 m/s from the north, what frequency will observg1p1;+(gtoumc 0 h don,(mo uiers 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 movin+ rf6en w-*lkkg on land if its speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where the speed of sound is ;73qu9xj amvj310 m/s (a) What is the angle the shock wave makes wja37j9 umq;vx ith 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 atmosp w5qx,nk:djp0iwniden/ 0; c) here of a planet where the speed of sound is only ab5q:c0ii ,wk n/d)pn jn0;dx weout 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s strikes the ocean. Determine the shock wave a4 0s99i kur*cmp byq,nngle it producesc9s,i 4bn mup q9ryk*0
(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 bo/u rzblwi; xb5 y858$/theta$ 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 -33oja tlb9 mqxc:q d,above the ground flying faster than the speed of sound. By the doqxq-jamb 3tc 3,l:9 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 that :kh eda* /oes1sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects ec1skeh*ea/ :d ohoes. 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 ma6odm2qjrad;1h yl 2yjl017bj 3 nbpu +ny octaves are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists of manypd43y*oymujul fl/a,v xv1dw0 0r.n3 plastic pipes of vdwj ,lpdxua3r 04*ufoy/.01 y vnvl3 marious lengths, which are open on both ends.
(a) If the pipes have lengths of 3.0 m, 2.5 m, 2.0 m, 1.5 m and 1.0 m, what frequencies will be heard by a visitor’s ear placed near the ends of the pipes?
$f_{3.0}$ =    Hz
$f_{2.5}$ =    Hz
$f_{2.0}$ =    Hz
$f_{1.5}$ $\approx$    Hz (Round to the nearest integer)
$f_{1.0}$ $\approx$    Hz (Round to the nearest integer)
(b) Why does this display work better on a noisy day than on a quiet day?

  A single mosquito 5.0 m from a person makes a sound close to the threshold of hj-5xe7 jimqw l 2 rbo/y/)wdd/u ij/e2xo wj ml/)-/q7dw y5rdbman 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 87-dh ;fh g0lt1 u (rnptfsq/;41yx1n sww3B sound are heard simultaneouslyuq p11wrnnh 01;yw;4fxh/3 gst(f lts?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 dB. What icdu6;fdy b h6 1yz*vc1 1l(kbhs the acoustic pobyd1f *u6lbk;c cvy 1hh(d61zwer output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rate pe2wy7wi+ dy1 9v2zqyd at 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power output in w pq7+ydv2wzewyi y 192atts at 15 kHz?    dB

  Workers around jet aircraft typiqsxbp /l/,x04ul m3y 8 /xzbqxcally wear protective devices over their ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 d,q / xqls4xbuxlm3/xzy0 8 p/bB, and that the average human ear has an effective radius of 2.0 cm. What would be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, the gain,dupn1e696k eq zjj zbkq42z 46 $\beta$ 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 fl;fblfu- .ua21 cvxlr* 8yo. frequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long betweenm,0vml 3iz tjw5w9+du fixed points with a fundamental frequency of 4400w vm9im,+ t5zudwlj3 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 vibrz2; 7xj+r7 qtmi 5qdnhation 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 wheh7zd2jxr m;+ q n57tqin 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(3u2lc)mqbpg is open at one end and also 7(pcqb32um l g)5 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 observed 9skyu , e jv/)o2cwx+s0 wx3jvto 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 sou)1i. t.e 3-+wopvzjielo m8kvrces. The sound is louwzk.ee3 o jv1l-. t8m+) iipovdest 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 the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz w rm cb6nu j4g3du/)j2hhistles. One train is stationary. The conductor on the stationary train ug)bu4d2cjnr63m / hjhears 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 538 Hz. jcrj /(dqp- 3oAfter it passes you, its frequency is measured dq- o3jp( /jrcas 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimatq2xg 8xgtz7: re the speed of cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the strtgq2 rx87gxz :aightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11 H iyo;53 )modf1t(k aowz. The shorter one is 2.40 m long. How long is the otheram kow()yfot; di5o13 ?    m

Two loudspeakers are at opposite ends of ak j4qn,s+qgs2 v5 qso2 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 sqvs 2j2,n soq+45gkq (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 inhgy; beg(,5a; s-zt br the aorta is normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red e,- z5 ;rahbgtyb( g;sblood 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 whix2pcx c+ip4 gm;5wr)e le the moth is flying toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz.p cgre+mxi45px w2;c ) What is the frequency of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound pulses as it approaches a moth. Theru)c/od/(acz e:xq; g pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. Hoorgeu:)(d;c q/x/ cazw 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 onsl(harc. q 3z;mxu, +ke Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundamental frequency of this horn, and which overtone is rsau ck,qhl;m+(z.x 3 close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo lis zg6bn;gv60 zntening can be compromised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, and 2zzvnbg n;g 606.8 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 “sinb /cddu -xbd( dj76hy6-y )gzkging rods,” involves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other h d bxj- dyd6-7c/ky)z6d gu(hband. With a little practice, the rod can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the threshold of hearing fo5s82fc (9ihrpou0ch:7u e unmr the human ear at a frequency of about 9n hpc8huu(:s750oef c2 rumi1000 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 ground hears 4enl- s+q;ib+ mtc :axthe sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s+:;st iam4x+ne-lq cb altitude?    $ \times10^{4 }$ m

  The wake of a speedboao,3 m xm3sjll;t 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