What is the evidence that sound travels as 89k1nmw o:gc ea wave?

What is the evidence that soweuwev0ur* h0 p3t90 mund is a form of energy?

Children sometimes play with a homemade “telephone” by attjb6kv il.ok-3 aching 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 (Fig. 12–29). Explain clearly h.jl3 6bkkovi -ow the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you expect the frequency- yulro4kqsjm684oh)h69i jw or wavelength tom wk) 6yhjho6qir 8l- j4s4u9o change?

What evidence can you give that(- s977c5kteddxrdc h the speed of sound in air does not depend signifd (97s-ecrkh5d t7x cdicantly on frequency?

The voice of a person who has inhaled heax0c uu,4 3wbvk ke(uw-l if hka8)k;;lium sounds very high-pitched. Why?

How will the air temperature in a room affect the pib(gyfm * 85t0i2gj ymktch of organ pipes?

Explain how a tube mf u-w.n c;-bks *nkph2ight be used as a filter to reduce the amplitude of sounds in various .h -kc nws*-p;2b fnkufrequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced clq uv-qsi -55fdoser together as you move up the fingerboard to-q iu5vdsf5 q-ward the bridge?

A noisy truck approaches you from behind a building. Initially y0u,go+la4 wh7zer8y nou hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — w ,a4uoz07yre8 g +hnlyou 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,” whereas beats *cy4g ryf;l0ncan be said to bn0 fg;y*yc lr4e due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers werp, v yl(aa0m0de lowered, would the points D and C (where destructive and constructive interference occur) move farther0 ,aapl 0ydmv( apart or closer together?

Traditional methods of prottddry:sd+r)j qc b 8nmffj ;-ah7594i *sy ol:ecting the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise,yydalo5 r;cj nbm*9 :qd8dfi js-7+4t)h:sr f 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.h pp:ugn6nm9 ayk723 w 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in u96whpmp a3ng27:k nyFig. 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 sourcale a+v5bq2+i e and observer move in the same direction, with the samea5 el+a+ bvqi2 velocity? Explain.

If a wind is blowing, ws/i hp7 tf0ka7tf14mcill this alter the frequency of the sound heard by a person at rest with respect to the source? Ifkti47f/ ta mc1psh07s the wavelength or velocity changed?

Figure 12–32 shows variousg d5mpx 7ud0l6tj. q3nzx lm19 positions of a child in motion on a swing. A monitor is blowing a whistle in front of the child on the ground. Al6x u5dqj0 3m1d7l t. p9mzgnxt 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 lk44 rh-*fqbbe cwq v);-xr 3qwength of a lake by listening for the echo of her shout reflectek -he4qqw4 x3b rv ;-)wqcb*frd by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterlinkb(bl d,l)d7u, hiw9 be. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this poinh,lbbk 9 ubwild,(7d) t? 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 waveleng25bzu jksw5uo2f d ,y5ths 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 just above a school of tuna sz)/z5 ya, u+ -mfqicnon a foggy day. Without warning, an engium)zcn5qfy-a/ + iz ,sne 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 splashat5aac7h7 e s)ag8j1q it makes when striking the water below is heard )t5 e1q7ja8sgca7haa 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge -t,y5ckz7 i-j)qea rn)z2d*;xyaiu jstone strike the concrete pavement. A moment later two sounds are heard from the impactjj)kra;u z,iy7 ed*-c t)nq z5yxa2-i: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made oj86o*wa:eke*5hd j xx:j.di gver one mile of distance by the “5-second rule” for estimating the a:j8hijdd .ow j x:kg56e*x*e 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 lcj4safuo2fd4 .c/s+q a3k( ethe 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 ouva2ri *7ptr.:i8yq ey z,9zof a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of vs1 9r/+,ko rxt rl4cd)tv 9xh95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hx/, r14htvs d t9xcvr r9+)lkoint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally noisy w) uwo60ki* ovjet engines is experiencing a sound level bordering on pain, 120 dB. What sound lev6vo)iou w0kw *el would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise r3ry)i(jp y-; -tx; vsnelb s3gatio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities o(3-;rv yt-ls gxy3 i)epnbj ;sf the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person spc5 w1-dvsf;ur2as6yjeaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere c- d1us2sa;fywj6rv 5centered 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 es3c:cf:o hk7(zuhj wokni6 ;, ardrum whose area is $5 \times10^{ -5} m^2$ (a) How much energy is absorbed by the eardrum per second?    $ \times10^{-12}$W (b) At this rate, how long would it take your eardrum to receive a total energy of 1.0 J?   $ \times10^{ 3}$yr

  Expensive amplifier A is rated at 250 W, while the more modesq bux7e.au+1j, h. ft zj) hh8e.6bncxt amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connectedbhchbuau.nz ,qj. xe8 ) f1xe h+j.t67 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 inobem6ro ie:*ye+ (vdbna ;9j. front of a loudspeb*e (oednmivrjoe;:a+6 y. b9 aker 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 dq8b0uwrjraz2tl -4 4r B. What is the ratio of the amplitudes of two sounds whose levels differ by this amou2a r4jwltur r q8b0z4-nt? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intenh;;+ )u-pqt2*aulye io 6 wkepsity increase? Increase by klpuu*aiq;2+)h ewe 6y-t ;poa factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement npnb hd6t)a67 os0*sd amplitudes, but one has twice the frequency of the other. What is the rat)a*npsbd t6 d06 nosh7io of their intensities?   

  What would be the sound level (in dB) of a sound wave in ai v(knvczr0l4q ;fz:(( xgfg.er that corresponds to a displacement amplitude of vibrating air mo(fg;zfgl( cnvz4r e q0k. :vx(lecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem buyaho9,lg;)l e 0y7vas loud as a 100-Hz tone that has a 50-dB sound level? (Seeyl9,g;bvay eo7uh0)l Fig. 12–6.)    dB

What are the lowest and highest frerc n8at f64o8jtf;y( fquencies that an ear can detect when the sound levec64 fof8j( ;8 taytfnrl is 30 dB? (See Fig. 12–6.)

  Your auditory system can ahde ttv -qiszr(v0+w6d(/ i6qccommodate a huge range of sound levels. What is the ratio of highest to lowest intews/0i+- zre(tit6v (6 qdhqdvnsity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental frequency of tjfzi3 bov5.xl -v siz o;1o74440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension fz7 oj.l-31 i;45bsiotxvo vzmust the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental*t:r;h0oryo n y 0btfdlxd/ 28 and first three audible overtones 0odh /ofn*t l 0r8btry;:y dx2if 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 expzn q- tbvqj/.8ect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a cz8-. q/qbt jnvlosed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-tube pipes spanning the rangeloojul6c8;yz9 ur.3:3jmagq 3k 6qoc of human hearing (20 Hz to 20 kHz), what would be the range of the.ooy3 6r8zq jlkj6uc 9l cau:3;gqm3 o 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. Wr718re zj 8t0ucx 1gs) +zqwxmhat will be its fundamental frequency if r81e8s u7w1mzq czjt 0xgrx) +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 1t8 v1 mj6 b;0zoafwzbplay E above middle C (330 Hz). v0f 86;btwz1z jm1oab
(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 that4:-slrh1ey ox emits middle C (262 Hz) when the temperature is 21 osr:ye4h1l- x$^{\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 wa 6 sv,d(wz 96ba:h(nfmzh1a 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 t0oe4v wiud1i7he hole be that must be uncovered to play D ab4diw v eu7i10oove 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 resono+ oyq-kiwp6lrrs 5: 8ate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is a6ok8r5l:s-yri+pq w o n 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 bot0jim*uq ugj7 :l,w4uxh ends. It resonates at two successive harmonics of* u :m,4j7qxjlu0u wig frequencies 275 Hz and 330 Hz. What is
(a) the fundamental frequency,    Hz
(b) the speed of sound in the gas in the tube?$\approx$    $ \times10^{2 }$ m/s

  A pipe in air at 20 ziu v;dh+jb/v bol;m+9ex.e e(ez9 )v$^{\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 *7t rspntw1e9i0w4mb-m-long organ ps mibwr0w1ett 974p *nipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approxi,y/t g+;jo j yg0f3xfqmately 2.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of yourx+;jyo fj,3tfq/ 0gg y 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 two v1a6qh e0u qi8strings, one of which is sounding 440 Hz. How far off in 1qvi06 8 auhqefrequency is the other string? ±    Hz

  What is the beat frequency if middle C (262zcfx 6pf;j40 c 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 ope0y ji))md ;twe+wm 0bnrates at 23.5 kHz, while another (brand X) operates at an unknown +t0 )yj ;eww0mnmdi)b frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4; mh(ut9x /v:tz)cibb beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fori/uxvb ;t9)tzh ( bc:mk. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned 5x8, znoyl(an to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What zlxo8n5n,(a ywill be the 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 trun ppq9a2q0 5yy to play middle C (262 Hz), but one is at 5.0°C and the other at 25.n5q29ap 0 yupq0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, ae -8nukr/z*g fnd 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 frequencies are 8k-efru/ngz * 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 and*vurq9ealb 2zujr.( , 3.50,9vuu lrrqe*.j 2b(z a m from the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating at 132 Hz, but a piano tunalp5 e1: q1ncef;yg k;er hears three beats every 2.0 s when they are played together. (a) If one is viea;: 5cpgf n1yelqk1;brating 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 wav4 vxd2*d0 obryaj68cselengths 2.64 m and 2.76 m in air. How many beats per second will be h2*jsa4or6vb x 8dy0cdeard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a h.5l)dw* kmxa certain fire engine’s siren is 1550 Hz when at rest. What frequency do you d .mhaxk5l*)w 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 a fire engine whosl+5+.kubzhct 3ybs:.p0i q*mcozc/h e siren emits at 1550 Hz moves at a speed of 32 m/s /qm.0+ cstpih+5ucyk3zh*zbco .: bl
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz soe8 2d)4prn1ei9l e vbvurce is moving toward you at 15 m/s versus you movil e 4b2peen8d1v)9r ving 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 frequency horn. When ox 1omem 57ss(mne 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 emit? Assume T =mo1m(x ss m7e5 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receives a9k )f kiklhs ke)qy-5.v+d0c them returned from an object moving directly away from it at 25 m/s What is the received sound frequenfe5s+))y.qavkk-9 ihd0 kklc cy?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/sbfg,;:ig 857 rv+ q:-vc*rtuu p iuzky As it flies, the bat emits an ultrasigtzuv ;7q,c p-u+b:v yrrk*:iguf5 8onic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original 6a faz11 xnso0Doppler experiments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a spee106 aanxszo1f d of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measux kmx.kzrl08 ) x,c6vere 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 flowing in large leg arteries at 2z m)x.,vc 80ex r6lkxk cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonicq4mg 1u)irsn;)bj zoadgj +bq+i 1q5. waves of frequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emittwkg49oszl( 8 s sound of frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are located, z9(sl8tg ok4 wat rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if its speed at 20 (etenh u f620b$^{\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 sp6a3 qn1q,9xptkk5 k/.j (ufyny kts+jeed of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of (k 6y1s3pjkqn xufy/t+ na5q., tkk9jthe 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 atmosphere of a plane /jjj pd5pd r/di8)4let where the speed of sound is only about 3 5d jpei84dl/jjr /)dp5 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 t.fyett,z kzd, 1(,kgrmi t3v7 he shock wave angle it prodzdt ,3,rkttgimk, yev1z (f.7uces
(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 zj1+1 gv8qiouqz33 s/bpxv 2e $/theta$ 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 f15w fz,wp7 - .agpa.tbbn w4rzlying fasnta4 -bp75pg,fz wz..rw ba1wter 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. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device that sends 2pa epx- s -4..s7xxdgqx9nw g30,000-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 9.-p3xpgedn4asxw x.x s - g7qtime between pulses (in fresh water)?    s

  Approximately how many ocjihrs 98sy: d.taves are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a disprk51p6s*hxo 9 zuh tr,lay called a sewer pipe symphony. It consists of many plastic pipes of various len9pozk1ths5xu, h*r6r gths, 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 thresho6dk j)yii 2*xtld of human hearing (0 dB). What wij*x 2i6t )kyidll be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB soua:c fffb.f7e.nd and an 87-dB sound are heard simultaneou fc7f:b.aef. fsly?    dB

  The sound level 12.0 m from;rm(nd zj5.l pn w56cm a loudspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the speaker, assuming it radmm l 5 zjw6p.cn(;dr5niates equally in all directions?    W

  A stereo amplifier is rated 2pzvfpy320gpdr e2x/ at 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power oupypfx3z02v22 p dg e/rtput in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective . *ttanafgeqdg2;d9 , devices over their ears. Assume that the sotefdt,gg ;.nqd92aa* und 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 communicrpz/v6 :2pmun ojx8y / -iiy7mations 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 frequenc+z/nw rphm 6 -mqur 0mtjl91-hy 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 points with a fund4jb 7c-lg*5q5hf/v5i szrvy k sd.mw6amental frequency of7.m/gjchlw 5*5-qiz 4dfrysv5v b 6sk 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 int hm)kp5:hbr)io vibration above a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuninhkp b):ir5)hm g fork?   Hz

  A 75-cm-long guitar stcp ;x--awn) urring of mass 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 fundamental mode) with the third harmonic;rn paw -x)cu- in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resoqel i//xf/2nz tyu9- ynate 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 500–10c3qrp/l .o3r,o2q/hlzw ul *h00-Hz range coming from two sources. The sound is loudest at points equidistant from the two sources. To de/qr*2r qzl.puhocl l,who/33 termine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One tm7vzjy9a0 v+yrain is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequency whenv0 +zvjyay7m 9 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 if2ynobl ex(8veb(u-c 3 -h sg0s 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant ( s-bce2uyxb v(f 3-0en8golhvelocity)?    m/s

  At a race track, you can estimate the speed oik)mjd0s ;+k yf cars just by listening to the difference in pitch of the engine noise between approacks;0d) j +iykmhing and receding 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 11 Hz. The .m7lco ekwten i)8. +qshorter one is 2.40 m longewe.cl) okni+ m8q7. t. How long is the other?    m

Two loudspeakers are at opposite ends of a railroad car as it moves past a7 hjf ycpp*9j0 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 0*pj7 yp9fchj beat frequency heard by the observer when (a) he listens from the position A, in front of the car, (b) he is between the speakers, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in the aort(j qoj:5ib-ws*a5 flja 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 blood cells? Assume that the waves travel with ab*j: qi l5(j-jfaows5 speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at spee bh9jbqi4m ,c8nh9xj g16bop+d 6.5 m/s while the moth is flying toward the bat at speed 5 m/s The bat emits a sound wave of 5pcmbjo gn4xb,6j 8hb+q9h i911.35 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 sound puls*ok* xc wq(r4xes as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 mq*o*4 r cx(wkxs long. How far away can the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once r am2 bkcbzi.g83 ;c3cused to send 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 must be blown in such a way that only one of the overi3; 3cgr 2bz cc8ba.mktones 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 compromised bypeomq 28s,vu-gc 73l n1bn(fk 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 o1usfqemp 7n23vnl,b(k8g c-the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rvlt8arl-zb1 -/+vg (s t.rhub ods,” involves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emit a clear, loud, ringing soundth/r -l-8(lbba v+su1r gv. zt. 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 human ear at am zgwq/y;6 9nz frequency of about 1000 Hz9w /6y gqmn;zz 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 grouh qsg tw; -ad9;ck(ub.nd hears the sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s altitudh( sda;9.c wb q;tukg-e?    $ \times10^{4 }$ m

  The wake of a speedboat 40)nq( -+wzeg gl wydomqe (nfvo 6y//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