What is the evidence that sound travels as a wa:5by;p qtuxgt.x g1 4xve?

What is the evidence that sound is a form of energy5 z zbf70eu)tfe9iz(phz g22 v?

Children sometimes play with a homemade “telephone” by attachin9k17dfek :lncg a string to the bottoms of two paper cups. When the string is stre kedlk: ncf197tched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into wn: a ./mebl9qks pn16gater, do you expect the frequency or wavelength9bng:qk/ lampsn 16 .e to change?

What evidence can you give that the speed of sog,ggrj:8p g hqzwkf :/( ( d gsxvyfa;,yf5j03und in air does not depend significantly on freque jw0gsxvgjgy3afd:gf:/f z(yq5; ,rg 8, ( pkhncy?

The voice of a person who has inhaled h-/vfr8 ti 1e ywf8kvr3y+g,arelium sounds very high-pitched. Why?

How will the air temperature in a room affect the pit r/px0kx8a m8ich of organ pipes?

Explain how a tube migeqryuz ar*/j8 (xed) 3ht be used as a filter to reduce the amplitude of sounds in various frequency ran dee3(/ar ryu 8qxzj)*ges. (An example is a car muffler.)

Why are the frets on a l4 lv0scjs, 8yguitar (Fig. 12–30) spaced closer together as you move up the fingervsy llsc8, 04jboard toward the bridge?

A noisy truck approaches you from behind a y l-ceg 2q6n5hbuilding. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “qnhye c-562lgbrighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be (y wh6fzx*v3j kk*2zxdue to “interference in space,” whereas beats can be said to be due to “interference in x*y3jz*k kh2x wv6zf (time.” Explain.

In Fig. 12–16, if the frequency of the speakerwqcu( f dc)a90s were lowered, would the points D and C (where destructive and constructive interference occur) md0aw(9 qf)c ucove farther apart or closer together?

Traditional methods of protecting the hearing of people who work in a5fj+dg7a z s;creas 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 levels j;saz57c gfd+reaching the ears?

Consider the two waves shown in Fig. 12–31.db bp,q:1szc0 Each wave can be thought of as a superposition of two sound waves with slightly different frequenpd0z1,qs:cb bcies, 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 same directio g-tnah 44mlakm-j,6 zn, with the s4mh ma- zj ktng-l46,aame velocity? Explain.

If a wind is blowing, will this alter the frequency of the sounnu h hi7ay79sl j*.tfy),) kykd heard by a person at rest with respect to the source? Is the wavelength or velocik7, *yikyf auth)j9l7h n.)ysty changed?

Figure 12–32 shows various positions ob3tjs0v1-y bnf a child in motion on a swing. A monitor is blowing a whistle in front of the child on the ground.3-bbv st 0jn1y At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the *ipwoq13vgj .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 of thip3w.v1 qgo*j e lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his shipg7 tlt+q9ekt0o k 3lb4 just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 g 3b ko4lkq0+tte7tl9s 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 wada z :np5gangm(0x ):fvelengths 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 9ab/ rzssl enw.,qv-vm01+jv just above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). Ho/,-vaes v j9mblr.wz+1qvsn 0w much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the trh /ydu h8 evgs5k1txj.1-mg2op of a cliff. The splash it makes when striking the water below is heard 3.5 s later. How high is jdte2u58ry-h1.1 mhsg vx/ gk the cliff?    m

  A person, with his ear to the ground,wlb 79*d* zdgxdrox0* 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 thd0dzx9gdw **bx r* ol7e 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 over one mile of distance by theuto ;:em.sbg 4vkf:o 8 “5-second rule” for estimating the diskf.84mvu esbg;o :ot :tance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity ca,jp5vg. v-udm,mf o3m :2iuof a sound at the pain level of 120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of6wp5qz101jgs.ea2berzcl + z a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fire/s+3wvribzluql1wt0: ) mi1 m d simultaneously at a certain place, what will be0q u3w/b:tmvrw i+ 1mll)si1z the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from a5a n,2bw1o1wzcnjg9 nn airplane with four equally noisy jet engines is experiencing a sound level bordering on pcn5 jn b aoz9gnww112,ain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-nov+h; dd ofg50ub*.ivh ise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background bh. vugf5 0d dvhio;*+noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of soune 9n: lv)yi6(tq7gxl. bvj k :-vze5dzd from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads rtkq: bgv.z(7yd- l6nzel 5i ):ve xvj9oughly 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 stj,u/cj3s 0 akt ;jd1xmrikes an eardrum 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 25o)ak ct9piwlgp/w 0480 W, while the more modest 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 lot)cwl0k 89o/paw gp i4udspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registered 130 dB when placed 2.8 m in front bbxy -zs p,+-psg814w5udb fh5gcz:v of a loud pvd8+1z-xzu5:p-bbyshf , g cbg 4w5sspeaker 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 typicallyyok g f/+-ln4j detect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sjg + -/kf4loynounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a)hqh4fdd-l9w ttx./ b fdg/60e by what factor will the intensity increase? Increase by a fat.6 qblgx-hd4hfd/0ew/f 9tdctor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but b+ ,*p i9k42vv 1jggvqldn )ayfne5 6eone has twice the frequency of the other. Wn 6p ek9 2g,5d+nevlviyvjf4)g q1 ba*hat is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that correspo,wcco* yuw( qtb)5./ (-8cvvhlzaa1)stbpc znds to a displacement amplitude of vibrating air molecules of l c(caw,s-/81achv ) vcpwzqt)*uo.(tb y zb5 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tpqzz :1dq) ;gho.sfd0ejr: ;none that has a 50-dBq1 g;z 0 :dsn)fz heoq;p.:jrd sound level? (See Fig. 12–6.)    dB

What are the lowest and highest freq0upv 9id3vv182w5.8y tfr7aflyfxwluencies that an ear can detect when the sound level is 30 dB? (See Fig. 12–68lv 5.it8ffa2wuy1r790ypdv l vx wf3.)

  Your auditory system can a,vdck6 po- 3skoh.2dcfi os9 8ccommodate a huge range of sound levels. What is the ratio of highest to lowedkco9csk.vsh od-8 p3,i6fo 2 st intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental fr 5m8a 7,ia6 pa,qcnvgaequency of 440 Hz. The length of the vibrating p,a5n, a aai7vgp 8m6qcortion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the c.x s5:3brid(uf6p ytfundamental and first three audible odxcbp6y (5:fr.s iu3tvertones if the pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you elj wlxbv/ 1a:(cb e*c9xpect from blowing across the top of an empty b el (al/xcvj :*1c9wbsoda 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 open-tube p.q.l3pvo q6w wir0(d+1jciu z0tpg e- ipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the ran6 g3l(j +0r qvew -tiu.o p1qc.pzid0wge 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 s,5;2 k4x2tf1c wze h1s dghbp3ee o7pthird harmonic. What will be its fundamental frequency if it is fingered at a length of onlhd 7ws ee1s p,go2pz34;e chbk215x fty 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long anu4s1uft-1xohyn .f 8f d is tuned to play E above middle C (330 Hz)x1 h81yton4fus f -.fu.
(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 emi kqi9e/1,yljz6 xzlrr- :+vihts middle C (262 Hz) when t6erjh1/iizqxy+- ,l 9 klrzv:he temperature 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 lqyf+klm-7dpi+ yb;)at 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 1c934 ey 5hd iqgq(6weo2–10 should the hole be that must be uncovered to play D above middle C at 294 Hegy(c659q oieqhwd3 4z?    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 pipe4) pnp-os1kug can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or a clo1)s ng4u pkp-osed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at both ends. It-j / 0crvu1ttt resonates at two successive harmonics of frequencies 275 Hz and 330 Hzt-1jtvru 0/ct. 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 o n-05r:wejq* db.inz1ru d)o$^{\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 prese3a zx 9oyqtr1:nt within the audible range for a 2.14-m-long organ pitox39a yqz:r 1pe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long.9 v4ex q7iskch*gy*1a 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 your answer to the informatio*x7*keh1c9 yavqi g4s n in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one +bviqj c0e374 twa8 pwlymo 9(beat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far4l(w qpicb+tva8j30e9 7 omwy off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz) an6d e;3xe6yg t p+z+frvd $C^＃$ (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+ktu .2u0o.+cx sb3fun 4rnxi at 23.5 kHz, while another (brand X) operates at an unknown frequency. If n2n.nifx4b+.ks cuu0x r+ u ot3either 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 beats/s when sounded with a 350-Hz tuning fork any)/5w.d5 b z6kqsjqi8kuh i.sd 9 b./dssy.k w b6qqk5i5 jui8h z)eats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the sayq:.,n oak.oj me frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–j n.,k y:q.aoo13.]    Hz

  How many beats will be heardqpvc1,-.: uislfgzo bd/ pl18 if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the oth lpq p1 soidzuvb .lc1f8g-/,:er at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks x1c: vhlq7dcb( e/e;r, A, B, and C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are sounded together?7h;x:e lqcrc(1dv b/ e$f_A$ =    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 mq3 zgbms n;i1: from one speaker and 3.50 m frog nbq3m ;:zi1sm 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 vibradgjuhl- :45u,s8xr2 0 o3jdpjq(gm upting at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must u-s5 md (ug2g3p jdjul0x,qo p:rhj 48be 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 zfy4 r a140pjeand 2.76 m in air. How many beats per second will be hearjp404e yfaz1rd? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s sir p*iqu31 otr*jen is 1550 Hz when at rest. What frequency do you detect if you mipr 3q *otj1u*ove 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 who 6 p kc:td;yht0*rwa0e+ +bwtwse siren emits at 1550 Hz moves at a speed of pawctt +br0k *y whd;tew06: +32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving5s;dz+q/huual 3*8t stn:r gynui+8 d toward you at 15 m/s versus you moving toward i;lq:/53iugrdu8sh u t+ sa+ndn8y*tz t 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. Whevbzm , drhv0 ip(o3),wn one is at rest and the other is moving toward the first aw)3m r(v id0hp,o z,bvt 15 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 a ahdytn: u/5m:nd receives them returned from an object moving directly away framnd5 yt:: /uhom it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat emits an ultr a )na7db)w. g1e0ywogasonic sound wave with frequency 30.0 kHz. What freque ny)begw) .aag 1w07doncy does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba w o87exjttr, 2ras 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 tht7to errj,x28 e railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeds. Suppoctc2a ;ucdq -09 uzls1se the device emits sound l0a92 1cucusq -;td zcat 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonil/9a0 alnym3 d;axiz7it 4 e.mc waves of frequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequency 570 Hz. When the wind velocity is 12me)j x,h8h87c3vxn : nde8jza m/s from the northaxnx,h e mj 8n3 d)h7:jcz8v8e, what frequency will observers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land wtdoaa0 46ca -ibe/:t 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 sw 5gr):7 j/mqzudav4 opeed of sound is 310 m/s (a) What is the angle the shocvmz/ a5 4u)g7jw roqd:k wave makes with the direction of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmosphere o tveh*sv5 7q8nf a planet where the speed of sound is on5esq tn vv8h*7ly about 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/y3v*z i0ka+yd s strikes the ocean. Determine the shock wave angle iyz0adk3vy*i +t produces
(a) in the air just before entering the ocean, $\approx$    (Round to the nearest integer)
(b) in the water just after entering.    $^{\circ} $
Assume T = 20 $^{\circ} $C

Show that the angle )x0im+4hv nbysrgb dt gsrz::4g+(m *$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and seea ii4s2h ey.e(6 8zapq a plane exactly 1.5 km above the ground flying faster than the speed of soa h8esz(i p2q6i .yae4und. 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 th w-q)f4xcb-gg at 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 tc-f)bwgq4- xg he minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible rangk ::*/- b-k tmdk*aj5jyhfub5rh d i4le? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pip() pgj 5-:vuvw nd ::gpste)pze symphony. It consists of many plastic pipes of variv - np5)( e:t:jpzpg:g duv)wsous 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 thw i8pat,t n2j9reshold of human hearing (0 dB). What will be ,w i2a t8t9pjnthe sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-d.ntve(/s. - bdt8z eunB sound and an 87-dB sound are heard simultaneouslyeb nezdt /n-(.t8u s.v?    dB

  The sound level 12.0 m from a loudspeaker, placed in the opv b);)v ppcct,en, is 105 dB. What is the acoustic power output (W) of the speaker, assuming it radiates bc);p,vt p)v cequally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The poyvk g-z3n xc:c5k. qdw i01yp(wer output drops by 10 dB3xvky1.y-5qkd(p0 n:c c wigz at 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over their earia:i -cl7x ix7y b*g4uxx9 sg5s. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the power ingxbl:g9 xy7i 74uc axs5*iix- tercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communicve(dfny(s(t m n-2hdai64 ae0ations 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 violi hb0xubz 3 ;h lu00ri5/hmi1rsn 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 ii -ji/m*kzx *ts 32 cm long between fixed points with a fundamental frequency of 440 Hz and a mass pez**jmi i -/xktr 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 agw7v1haaqqk b+ -(w*rbove a vertical open tube filled with water (Fig. 12–35). The waterw- + wkq(q*hbrag7av1 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 tuning fork?   Hz

  A 75-cm-long guitar string of mass 2.10 g is near a tube that is open at ork1 l:knwg235v:vio-vzk )g*ea pfx8ne 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 igl3e:p5 r 2z fx: k va)gvk*vnio-8k1wn the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one full lo 7yp wwq0jo ge;ozd4l*fqg0ba*3s t. .op ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz range coming from two sources. Thkct (t1 uen:n5e 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 fart uc5 k(tt:1nneher from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz xsfd/xxn(pk c-r0h-( whistles. One train is stationary. The conductor on the stationary train hearsn0h-kp (xr( -xxdfc/s 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 iml1 fhob( 7no*t approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant veloci (fn1ml7*oob hty)?    m/s

  At a race track, you can estimate the speed of c8 r+d+wwxms kqjht;-6ars just by listening to the difference in pitch of the en6d+-j wq mkxs+tr8;hwgine 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. How fast is it going?    m/s

  Two open organ pipes, sounding togethetvp1t p1+48eajq t( our, produce a beat frequency of 11 Hz. The shorter one is 2.40 m long. How long is t(4a8p+pto1e tt vj q1uhe other?    m

Two loudspeakers are at o d8 1atcx-nvvq*28 ck c:b1xtapposite 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 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 t8t18aa*:q x21c cn -bdvvx kchave passed him, at C?

  If the velocity of blood flow io bvhv/yh6(h* (ebk( sn the aorta is normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves w*yv6bhsk ebhhov((( /ere directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s while the moth is flying towi 5vyjj3bs1x*ard the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of the wave detected by the bat after that wave reflv j51*y3xsbij ects off the moth?    kHz

  A bat emits a series of high freque05u*4 dzkwpk sncy sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bd 504u zswkk*pat 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 signallhg 2nc8 830wyzh qk0vs from one Alpine village to another. Since lower freq 3n0kl8h y0gcvh8wz q2uency 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 close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be co5cu-y tzl* +fk u9 ds/vlospc ht+a/;9mpromised by the presence of standing wave tfh+a*/vc su9pz-l/5+suk t 9yodl;c s, 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 the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, slender alumihgr )ytoi;; xbhtrv2 8*4wz i1num 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 cl i ryv1wgb i;;o4h 2tzxh*r8)tear, 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 t6khy1htm;x ) tpt: 2cchreshold of hearing for the human ear at a frequency of aboc htkp;ht:yxt26m c1)ut 1000 Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An o-. r:kojmeoda ml ji:q 515i4wbserver on the ground hears the sonic boom 1.5 min after the plane pawm5:1rekqjo-5ldaij 4m: o .isses directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is khkq +/xer+pvc:0 l)m15 $^{\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