What is the evidence that sound t2. h7 .ddb+ljks yf6jiravels as a wave?

What is the evidence that sound is a ffssf9urlx,j(n 1 kc ,(orm of energy?

Children sometimes play with a homemade “telephone” by attacj66u mibu:evl o6pu,,hing a string to the bottoms of two paper cups. When the string is stretched and a child oe6,ujlm,6 :ui6bp vuspeaks 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 water, do you expect th3y c dd5+yk4m6aofig)u 0o7b h7qfpf7e frequency or wavelength +7goco7 5q4f d6ih)0a7kfub 3 ypymfdto change?

What evidence can you give that 14hsn +m1zm(cchk)va the speed of sound in air does not depend significantly on frequemsh(k1 a)zvn+ccmh14 ncy?

The voice of a person who has inhaled helium sounds very high-pitched. Wh0ig whk)n 0p.fy?

How will the air temperature in a room affect the5h)unu.oeyewwu2tlnj43 - u . pitch of organ pipes?

Explain how a tube migi 3m siai(a/f1ht be used as a filter to reduce the amplitude of sounds in various frequei(miiafs a31/ncy ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer toge5tn ,mz4x38s ;p*lv ein ujje:ther as you move up the fingerboard toward the bridpe*u8zv:sj;ni, j x4 m t35enlge?

A noisy truck approaches )/vuij ,+ne j8w o*lrpyou 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 hig+, unp *jw8rlijeo/v )h-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “intudss(, ,fe zsovv5lqc)4s1ft; l8 p+derference in space,” whereas beats can btvs4,d5usdl)f(lovf;sp1qc z+ s 8e ,e said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lower/gs md-e kdmb2xmkqm 3be(ts.ms+*24ed, would the points D and C (where destructive and constructive interference occur) move farther apa 2s*+4mkmbe2s mqe -(dx/mm tksb g.d3rt or closer together?

Traditional methods of protecting the hearing of people who work in areas witt 8tydb(q4rnt2. gfm*,g/hg- w *(mcmt: dbwsh 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 coqrmwtft g,*8g(bh.*(d t: g wbs 4mc-ymtn2/duld adding more noise reduce the sound levels reaching the ears?

Consider the two wavqx1- :bz3nw3.1 y7ikeb ka nzaes shown in Fig. 12–31. Each wave can be thought of as a supe waqeb1:ayiz 7kx.k33n1-z nbrposition 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 observe3abns*lm3 6qnr move in the same direction, with the same 6qsnbm3aln *3velocity? Explain.

If a wind is blowing, will this alter the frequency ohm sb/ a)/y6+(dbp s39zfy+ y;tiak ygf the sound heard by a person at rest with respect to the source? Ig/dbyt i(fbakp z+ y6yhas;m+9/ 3)sy s the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monitor l(4*d k6j bcweis blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your c4jkb ( 6dwe*lreasoning.

  A hiker determines the length of a lake by listening1s0sk)m 6 msooml5lau46l /o v for the echo of her shout reflected by a cliff at the far end of tolmssko/16mv4s) o5 l06m l uahe 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 hislq:u ixpzk +y;. pn43t ship just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep ypz+ tix n:.p;lu 3qk4is 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 in aiq ejbbs rvx 80z8b ;)uz:thj09r 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 drifepks tzui;fh9,1 r2h+xi 1 ur+ting just above a school of tuna on a foggy day. Without warning, an engine backfire occ+ ,si fkupzi1e1rr+ h9xh2u;t urs 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 splash it itm0bg dox4ch/w h(jb32f8i;makes when striking the water beloim0 ;b3i8 2 cxjgh(wotf/b4dhw is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear vo/j n jv:ez- pg/s,6fto the ground, sees a huge stone strike 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 apar:sen oj g z/fj,pv-v6/t. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-second rule x 5ta 9mv.r;h7p1kf5cbvhr- u” for estimati. x55a;p-rbkhvhmurf9 t1c7 vng the distance 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 1 lc tlfir0gj2yb125ppain 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 leb-gfwy.8zd x cx :yk ,neuj./c4)ck7yvel of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 9zs; vvjds6xe+1x j: a*5 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not;x jss xj6 +ea*:d1vvz dB’s.]    dB

  A person standing a certain distance ; ;zho. wr-ku; ltf1xqo6a1 hyfrom an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level wq ow;x -fh.zar ohy1kl6;t; 1uould 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 ratio of 58 d:c m;31::ugdzn p ka,yyi0*pxh, x9 e2mogulmB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signalzg;k3cy ,puogd*lhpmx yaem, nm u:1i2::x 09 and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sounos20g,wlm -av 8p/9 i2kai3,ychtp sc d from a person speaking in normal conversation. Use Table 12–2. Assume the sound sph,22ws,0ov/-aistgk 3c pp9acyml8 i reads 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 whose area iszz +* b,)goq,zoi4nos $5 \times10^{ -5} m^2$ (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 th ;)elgjl0gou -xx/x4+fh:i3 v1ip k5s, cana he more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you woulfaxl, cehh)ig n ukox5-3g/p4 al i0 s;+vjx:1d 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 regk o- pqp:q2ufl s)36ghistered 130 dB when placed 2.8 m in front of a lohkl fuq2g 6-so q)3:ppudspeaker 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. yd:cyo7(ny 8g0 dB. What is the ratio of the amplitudes of two(yg ny78:do cy sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor0;gu;* .v*j cp( ecz7t vervhi will the intensity increase? Increaset* 0 c;jvzi gcr*pu7.e h;e(vv by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement au,:7()9 tdqsxz ze;f2 qkkbcgmplitudes, but one has twice the frequency of the other. What is the ratio of thq,9tce2; )sq( :bgkx udfkz7zeir intensities?   

  What would be the soun9 rif:icwkx udiep4d ) *snb+7,x8+svd level (in dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating b 4r,se s:8id p+wni*7 d)ux+fkc9v ixair molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what ,9sw fdh gwb8k.7.tnhm8mf -.zxy h1dsound level to seem as loud as a 100-Hz tone that h-hywk,x 7f.z .1mgftb8h .w8n9mdd shas a 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest anzj( 0 t/;qiiphkz/ u8nd highest frequencies that an ear can detect when the sound level is 30 dB? (See h0z/8n zkq/jiu(it;p Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What iskf2xmtj 01d b8 the ratio of highest to lowest intensitykmf08j1btd x2 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 fundam hj;9 -mjoqaj,n8avx 8q9 .qnzental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under ;qa89xm.nj q,- hq v9 zjaj8nowhat tension must the string be placed?    N

  An organ pipe is 112 cm lyl9cjbz9 /fgh1 3pl 2jong. What are the fundamental and first three audible overtones if the pipepfjz 9 gh32clj1/ylb 9 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 top ofgwz9tsyr4m olpwwi0 1 kz+:qf 5 lg579 v)wg8c an empty soda bottle that is 18 cm deep, if you assumed it8ggsp mw495rwq yw lt +7 o5k:gwfi)zl019cvz was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pipes spanning abtji z wy:30/ -df-sathe range of humaj yda 3zf/--wst0:aib n hearing (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 has a frequency of 540 Hz as its third harmonic. Whm3b-m3r fbz5z d( ttv4d rx15iat will be its fundamental frequency ifi 5mb zvr3t bzdd45(tmr1 3f-x it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.731:6prxo ta8 uk m long and is tuned to play E above middle C :6rk p ta18oxu(330 Hz).
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that emits middle C (2ri)+o*/p-o)ecsup * v dv1f,zn )k:ctb ihq9w62 Hz) when the ted) n,i9c-ozv* ) oswf:rt/ qppb k1* )uceih+vmperature 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 atga4n ,v;qoey ykro 280 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the fluob*2.dz z;lzite in Example 12–10 should the hole be that must be uncovered to play D above middle C i.*2d;o bzzlz 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 b:8vaz7p ( ;jwim(thi 264 Hz, 440 Hz, and 616 Hz, but not at a: 8z;wh(ji vpa7b(timny other frequencies 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 l75 v f9al*uxwwkadkn+jx /+4 both ends. It resonates at two successive harmonics of frequenc 4au l wfwk+x9l/*kjvx7and+5 ies 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 .ij slc9 ;w.jw(ey7dco*;z fi$^{\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-jt g;a b,*u;kv kft*mr h:c-9 6ihst2zz0 r6salong organ pipe a-0 mb jai,hk;hk:a6z*sr ut rz c;f6vt*sgt 92t 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately v1jmn xvq9djb/r1 6bj4 (fi*k2.5 cm long. It is open to the outside and is closed at the other end by xvd /9ikqbv1n41 6jj frj(*mbthe 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 too5vpo tcpui(6iw0 1gv g7*/qb adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the othq cg/b 0upvoo7 *t1vigp6wi (5er string? ±    Hz

  What is the beat frequenc7 v(dx n3tt -p7bdguy1y 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, while another (brandbv4sh w 5vk0,c X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately,hwk4v b v50cs, 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 a*b z; cnno4qjt+lr41krm 1 clkf21y:350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What i1 qznml*tky2rn4:;fa41 l bok+cc rj 1s the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings arjk +509j,/xvz( dkv fxpyjp, ie 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 t vjkv9ppdy5xzj( xk,+ if/j,0wo 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*vh*n;,aup rtiddle C (262 Hz), but one is at 5.0°C and the other *rhnu;,pa t*vat 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency tuajkp65b r48of 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 frequencies are possibleapr648kb utj5 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 fr.o1qmkk2gw/t+lkx7vi 1 e*gaom one speaker and 3.50 m from the other.kgetx g .1 /l2mvq7awk io*k1+
(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 bet /*cd32renfn9ml oo7 vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibc*n7ntr o9 / dom2fle3rating 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 c pn/n s+(8ohhmta4s-wavelengths 2.64 m and 2.76 m in air. How many beats per second will be heard? (A+8mhsn a t-c(s/n4ho pssume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 15rvqt o d;/1/gj50 Hz when at rest.;1 //r gqjdvot What frequency do you detect if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if spby2b 36yjt6whn/5u a fire engine whose siren emits at 1550 Hz moves at a speed of 32 5 p thu62w yn63bj/ysbm/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz so wry/*vgl23lsurce is moving toward you at 15 m/s versus you movingys/ *rlgwl 3v2 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 t nz)x,4 s8 ,w lmqz51vg3nxpewhe same single frequency horn. When one is at rest and the other is moving toward the first at 1v w53npg,)4nw8zx1ms zql,x e 5 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and r.ata8aj-,v qlxmawxrfh*n b)2 h;:, x eceives them returned from an object moving directly away from it at 25 m/s What is the received sound frequenc-aalbnh 2 qv;m8,:a,fa xxw *.rxh)tjy?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat ojbt(ik5g w e,p7z++u emits an ultrasonic sound wave with frequen e wiztj+ ug,ko7(p+5bcy 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a ttd 4di( )cguy:uba was played on a moving flat train car at a frequency of : tgidu) d(4cy75 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 ultrasounrk(fat*5m l 68l.riiv x25 zvpd waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is takav lrtplm652i kr8x( 5vfiz .*en 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 wgovij f(x7yx0r* x ,jtg26xz8 aves 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. When the wiy3d8( w3 e*p jwfurn*ind velocity is 12 m/s from the north, what frequency will observers hear who are located, at ryer(*dwp 3w3ujf 8 *niest,
(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 landfaifq4(p9 e y0 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 Macwp1:/xw -y yt -.(iswg5r, ymrl7uhksh 2.3 where the speed of sound is 310 m/s (a) What is the angle the shock wave magms-wtr:hxw- y wy/ .(,5lir1ys 7 ukpkes 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 t; ofai1 n/r8gahin atmosphere of a planet where the speed of sound is only about;1 gi8anrof/a 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 850092v-30pmujf.j g ext.h 7hfgg m/s strikes the ocean. Determine the shock wave angle it prj-7.m.0x hjft h vfge2g9pgu3oduces
(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 b)u8:yz,twxnes5b( n vkepe:d79 1. yk-e sze$/theta$ 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 fly lweh5hz; (gdw3f9 1zzing faster than 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. D(wfgd;zh lzwze 5h1 39etermine
(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 sg6lnt2783uxaykrb ( monar 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 to work is 200 m, what is the minimum ti3 kn762g8matlby r( xume between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible *h(+pfetu r:rrange? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists o+hv*ix sd,jd l) coeg)1b1c)qf many plastic pipes of various lengths, which are open on both ends. ecdb* is1 j))hgdx v1+,o)lqc
(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 from88q7ck0ax un3 jz0n5k crh;ej a person makes a sound close to the threshold of human hearing (0 dB). What will be the sound level of 1000 such mosquit nq3akujh75ec08n z8j 0rk;x coes?    dB

  What is the resultant sound level when p(0 3lo;) q lmy rr8-ioopw+lwan 82-dB sound and an 87-dB sound are heard 0( 8p3mroi+polwloywr q;)l- simultaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is uqdq 7zbk 5845xsiq*qpx m3oqxq+5w 7105 dB. What is the acoustic 8oxqkz74qubp5w q smdx+x3* 57 qqiq 5power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W v -emj)5wkfe)output at 1000 Hz. The power output drops by 10 dB aevke) w-mj )f5t 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over their e-tzog ff(if 6 fq7ye+1ars. Assumeo ftyfg(67e -+izf1f q 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 the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, th to12)u90 d3gy- vr gqdht5hrxe 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 violinyey z 0 rlm4ku(0 h7psyzrtz 6s .ofpp889r,y: is tuned to a 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 b e+0n b7agjit3oy mu5,*wyx9 zetween fixed points with a fundamental frequency +zae 9o3um yitwx nbg7,y50*j of 440 Hz and a mass per unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration above a vertical open tubezlpte 6cumr8cr+av3b( q;5- z 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 tuvc5 tzqrb c8z;-per+3 6(mlahe 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 m 8mh,rm7eew u3ass 2.10 g is near a tube that is open at one end and also 75 cm long. How much tension should be in the string if it is to produce resonance (in its fundamentar8 ,7mmw3 uheel mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as on;; gyc9i jvxqh81k2n -d5 osjne 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 com rs+uas(k co/+,x:oz ming from two sources. 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 level is minimal at a point 0.34 m farther from one source th+o +zc:urk,xa/ sso( man the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary.vc ,ebk+f(aq 4(n-gm o The conductor on the stationary train hears a 3.g f-km cn,4abev( +(qo0-Hz beat frequency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a stefn0 viw *km-- m.joan5am train whistle as it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving (assanmnk-.wfm -0j5 o*vi ume constant velocity)?    m/s

  At a race track, you can estimate the spexgmp xz4*k9y+3w wzf2ed 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 straightaway. How3fxpywgz m 2k *+4xz9w fast is it going?    m/s

  Two open organ pipes, sounding together, pruh.p+lh 3 n0nvoduce a beat frequency of 11 Hz. The shorter one is 2.40 m lu.hv3h npn l0+ong. How long is the other?    m

Two loudspeakers are at opw;chw x*fmy k5ot e (-indk855posite ends of a railroad car as it moves past a stationary observer at 10 m/s as shown in Fig. 12–37. If the speakers have identical sound frequencies of 212 Hz, what is the beat frequency heard by the observ 5cdmt(nw55ikkoh; fye8-*x wer 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 yb,1sgc2 in fm,w :n/kaorta is normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed alowb n:n,,1/gicf ms yk2ng 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 the moth is flying toward the bkubn nn l22( uo*z*r2nat 2 *b2lnzo *kn2n(rnuuat speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency soun0fq:je-/c1 r6 i0qikbme2gxj d pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long.c 0 e -/gi1qbk6xjmr:e 2fjiq0 How far away can the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to zkgqd 581m t/wy u;kt4send signals from one 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 m8/w1kt4 d tq5gyzku;must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundamental frequency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be c4+/i*hbt gmw ink(j4t ompromised 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 2.8 m high. Calculate the fundamental frequencies for ttj*( b i+i/w kmth4n4ghe standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” z :ian1o2cvui/0d6ddaj+ o 6z involves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, loud, roca0ii/av6+ z6 o:dd 21ndzujinging sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the threshold of hearing for the huma,erah f+r :jj :og9y/un ear at a frequency of abo 9/+r:eo, :ujf yjagrhut 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 Ma)o +ub, ea6jkvch 2.0. An observer on the ground hears the sonic boom 1.5 min after the plane passes directly a6juob+ek) v,overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat i+pko/g3-g,k n ioaes8s 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