What is the evidence that sou;s*8h-h *5tspsprruw nd travels as a wave?

What is the evidence that shy0+ ov iwj;s.ound is a form of energy?

Children sometimes play with a homemade “telephone” by abm :2j4bqg p/yttaching a string to the bottoms of two papp2my/4:bjg q ber cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you expect the frequenc 9 zdx9*;v rt2yfup:ddgx-a,vy or wavvfddtv: 9,y2p9 ; xau-rxdgz*elength to change?

What evidence can you give that the speed * /p-m/4nzkobb 7v zqaof sound in air does not depend significantly on frezobbz47n-pmq/*k a /vquency?

The voice of a person who has inhaled heliur/f(h 8b, z 8hduxcnp(m sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of o)py5chix,ooo rmi26;ha) ku+rgan pipes?

Explain how a tube mighu+ln,j p3 a2*et ymixdh0)nd5 oh 4z.mt be used as a filter to reduce the amplitude of sounds in various frequency rangesndy)h.ti*02 xoahzj+e 3 p5num4dl m,. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30k s gqbuakrxzt 5z 8w2rd8+,(0) spaced closer together as you move up the fingerbot20w 88x(ar5 ubzrqk ksg+d,zard toward the bridge?

A noisy truck approaches you from behind arig is* 1*nk*c building. Initially you hear it but cannot see it. When it emerges and i*n*rkcis1 g*you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in 5 :hexxs 5xkt bl(k00ispace,” whereas beats can be said bxi5kl(0 x teh5k s0:xto be due to “interference in time.” Explain.

In Fig. 12–16, if the freque( 7 9yhqr*cf4l9y;lw b p1rnejncy of the speakers were lowered, would the points D and C (where destrucj4 b y(c y1nqhw*9lf97rr lp;etive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearin0ndribb2)2b f g 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, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sound le0r2 bnb f2b)divels reaching the ears?

Consider the two waves t(fjgjaz j:p1 jgrb)l *1-w -rshown in Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different )lgtr(z1a bpj:1jfj* rwjg- -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 sourcq*7 fsbxsj i()e and observer move in the same direction, with thfi(jqx7s )* bse same velocity? Explain.

If a wind is blowing, will this alter the frc h n6):d -spbv/;ervaequency of the sound heard by a person at rest with respect to the sour- vhp/dca6bsnr: e;v) ce? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a chix 6v hgxv93px8ld in motion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which posixvx36 h pvg98xtion, 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 vam3rsy+7fb ; the echo of her shout reflected by a cliff at the far en m7bv +f3ya;rsd 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 *vihdav.9 /w tship just below the waterline. He hears the echo of the sound reflected from the ocean floor d9v*wi/tav.d h irectly below 2.5 s later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air ack1(i4 clz +brt 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 tuv i (65weso4 vodb*x379nlhduna on a foggy day. Without warning, an engine backfire occurs on another boat 1.65hd9xoslb weno* vu43(iv d70 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 makes when strikin-4erfyy9cp 1dn5o4f:myv u r 8g the water below is heard 3.5 s later. How high is the c vrym5fuce -4f9 po:yr1d8y4nliff?    m

  A person, with his ear to the grou994bcl9gg iws;uoz. jnd, 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 4gb. ;s9 l9i9gcwjzuoconcrete, 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 distan, /eo/4 s6pcm3wtgdqs ce by the “5-second rule” for estimating the distance from so6g,q3wtd/4se/pc m a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound d19cmn.l,salat the pain level of 120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of a sound whose +30b6rqc m2 scjx7 /)n kvt;hsg8 baisintensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level zy0 ub1 n);yxhnv)1 zk rj8a+nof 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’sn)b;j8n h zay)ur0zky nv+x11.]    dB

  A person standing a certain distance from an airplane with four equally n3g.0c1t -ggqu0gah rroisy jet engiarg1u-g0g.rthcg 0q 3nes is experiencing a sound level bordering on pain, 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-noise ratio of 58 dB, whereas 8h al4rinr7zdd ;:/h xfor a CD player it is 95 dB. Whi;8 rdlzdh74 nhr/: axat is the ratio of intensities of 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 spe. npnao2his +-aking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly nh+ a-i.op ns2over 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 eardqk8f vd*;da0 m h91w1r0 xwwefrum 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 more4a.+ad rkq9yp modest amplifier B is rated at 40 W. (a) Estird9.k 4yqa+p amate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registeredmen/jz : ks5.s 130 dB when placed 2.8 m in front of a loudspe :jmnes5sk.z/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 dB. What io26hgt.2f ct0nwub u 1s the ratio of the amplitudes of two sounds whose levelst bfu n2 6uwo12htgc0. differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, ( xzgeg(2 /7vbca) by what factor will the intensity increabx72 z( evcgg/se? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has zn- qgt3 :,ise, 12ndoqgku/lv) f) qotwice the frequency of theq)/ qntfo1nsu3zl,o 2g )-qi,d:kge v other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a s/0fg.xp vkl* found wave in air that corresponds to a di.f0g/f pl*kv xsplacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have wh6(/yfwbbgb4 cat sound level to seem as loud as a 100-Hz tone that has a 50-dB soundw6(bbf b/gc 4y level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect wheh5b;hn ;1.q gmo1.rb;i,a 5engp wurqn the sound level is 30 dB? (See Figghab rgow;mq1i5q.p;5,u h1be.;r nn. 12–6.)

  Your auditory system can accommodate a f) 3y4h st 94mrd4o(3 j uzzz2juew3nnhuge range of sound levels. What is the ratio os3feh9w 43udo4)zyzr u2mz4 nj (nt3 jf highest to lowest intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental frequency of 440 Hcek (z-w 4rof9z. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be plaofkz-9c (r4weced?    N

  An organ pipe is 112 cm long. What are the fundamental and first threnoux;l ph a(q8 e.t1syk-i5s: e audible overtones if the pipe is syou8hl.in1:5 -kxea p;s( qt
(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 frequen37ng0)9 scj0 bx dv5i cn9znztcy would you expect from blowing across the top of an empty soda bottle that is 18nx)vgn7n9 3zt b di50cc jz09s 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 c6e s6l9imoz*n5ueq, pipes spanning the range of human hearing (20 Hz to 20 kHz), what wo9 6onl* qsuz,e56imc euld 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 p4:vi 9u(gf6jlqsjk 62w jp8m as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its original6(wfu 89s j v6 qk:lpjip4mgj2 length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned tomgg,u2( bqtqi +c0 ;yj play E above middle C (330 Hz).0mbygjqq;i u(g2+ c,t
(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 orytytqnwa;+ 2 :uod 99ggan pipe that emits middle C (262 Hz) when a9w9tg:yu2d qt;o+ yn the 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 at 20 nli p:fwz71fl7u 4- ia$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Exam8k .cmgi 5ui)zple 12–10 should the hole be that must be uncovered to play D above middle C at 294 )zic5 .g8 imukHz?    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 e 12f6/v6p wmu;kj6prxq 9ayhcan resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Showfw p /9h ume16xj;v6 ap2yqr6k 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 both ends. It resonp2p*lpq+.q; qp mie )gates at two successive harmonics of frequen 2qpilq)*p qmep;+.pg cies 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 8a(u lr.r-z 9r*w9 lui5n/( ygp mmrvk$^{\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 withigfma+g .:v :xitzx z+(n the audible range for a 2.14-m-long organ pipe (fga+: gv zz x.t:m+xiat 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open to the outside a/7k6ihlet bcl)iy-hbs+ 3g+i nd is closed at the other end by the eardrum. Estimate the fret+ c6h+ b e 3igkhbli-s)/7yliquencies (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 tobj57zw hnx v0d;pq)n*g9dp ;rying to adjust two strings, one of which is sounding 440 Hz. How far off in frequencygq)p 95d ;7xpjv;0o *nwzdbh n is the other string? ±    Hz

  What is the beat frequency if middle Chy x;v+mhh h o1i41 02jijdr/a (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 anoth t(jb18 ny1ylxer (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, b(1by xtjl 8n1yut 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 fo0n:7v o fe9)okzl p-yzx9bku /rk and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain k b nuy)7zez olo pf:/v9-x09kyour reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension in ondi cke (3svy.sx g)(/ue string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall scg.dx()k ( y/ euisv3Eq. 11–13.]    Hz

  How many beats will be heard if two identicx.it.arexgq9u 5,r7fal flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other at xi x97,gu..f qerta5r 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequpu (tth- 3ibs9jwjl6 c7m j11wency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and Cbjt1wuj-1c3 wms7jl6it h9p( 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?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. w p.*.s4cwo, iji rnly8x(oue1d4 c *sy(i)ikA person stands 3.00 m from one speaker and 3.50 m from the41(*s,p (w w * iyioy.8dxk jsl)c.erniu c4io 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 )6inbz 9nq2xg at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating az bigx q)6nn29t 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 of3coce,+ zupq u .3a3ow wavelengths 2.64 m and 2.76 m in air. How many beats per second will be heard? (Assume T ,z3 ouo3.w+qacep 3cu= 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz /y(9u fqsjad(* azabm +/fax( when at rest. What frequency do you detect q(* f/u+dm9(/(byf a jzxaaa sif 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 freque*+8of( ekei( jxigt3 ht6le.fncy do you detect if a fire engine whose siren emits at 1550 Hz moves at a e hg8e(e*t3i6ox+f ( fk.lti jspeed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift heu8 v6d;em1pymkj -y(vic5 1 in frequency if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactlpv hiv6;ykyc 8-15( e1ed ummjy 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 sau lk6zy. ;fgu4x3;iydme single frequency horn. When one is at ldy. u u4;36kzyix;fgrest 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 = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonq,wr tu*dmty6/8ka ql 53 7qltic sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25t l*qm a87/ wr6dtq5ky3t,u lq 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 18t+gg 35l xql ()c i4 znjrj8xmzni*tultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflecte88z3zqx1 ltin j5t*gm)i4nl +jg c(rxd wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on 5z6gzcv f2l t;6huc(oa moving flat train car at a ;zch6vzuoc6 t52 (lgffrequency of 75 Hz, and a second identical tuba played the same tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speerj; p+guo 8f,ads. 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 f8+u,aopj r;gbeat 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 waves ou,6iln4e v yb*u *ogc9f 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 i/*2vv3vk k:iomg p9k. lp)ldu s 12 m/s from the north, what frequency will observers heav /9m *vd3kvk.pl p:)g 2likuor 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 lnj*dlhc6oe 01 and if its speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where the speed of plczgd +y/31qsound is 310 m/s (a) What is the angle the shock wave makes with g/ y+dqcpl31 zthe 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 ofg(f95ul/j qglre6f6 4y8 by bd a planet where the speed of sound is onlyg4fll6 yj8q b/d f5(ygubr 96e 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/s strikes the ocean. Determine the shock wave anctwd /.w s/xz8ezks gj5()6ctgle isctzs5cdt ( .j8z//wkw) e6gx 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 8(fo1hv.ov4i0hdb /8sejb km $/theta$ 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 kmgse fkj mb+4(4 above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal distance eg 4sbm4(fjk+ 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 c9c ig knh3 c;c /s6/2auuj27v;cdsqo 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum de j2iau; c;3c26 vncoc/gsuhqd79c/k spth for which it is designed to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are tjp19zz 0mbn- ehere in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It consists of many3x t;7yh iy72wc q.qrh plastic pipes of variou3yt2qihrq7wx 7yhc . ;s 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 fib2k(1isc-xh gdf.4dm w5 dx7rom a person makes a sound close to the threshold of human hearing (0 dB). What will be the sound level 2xidm1 c4bwfg.-5 xkid(7hdsof 1000 such mosquitoes?    dB

  What is the resultant soundhep axdf .vo+s3st y+s )z4:jahd+:7 h level when an 82-dB sound and an 87-dB sound are heard simultaneo ah:y z 4e+f7d.hsvhdt) x spj:a+s+o3usly?    dB

  The sound level 12.0 m from a loudspeaker)cp u5y*ft;) onkdb5 o, placed in the open, is 105 dB. What is the acoustic powd5oky 5*bc ;t)pnf) ouer output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated atz ,wmvek(us p7p1bgi.x 16vq : 150 W output at 1000 Hz. The power output drops by k,p7gzwms x:61qe. vbv 1u(pi 10 dB at 15 kHz. What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective dev y8s4 n0qwunf,ices over their ears. Assume that the sound level of a jet airplane engine, at a distance of 30 y0nfq8sun4,w 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 system2upqv,g:nqs2 a 4k.r5bakw ;ns, 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 ut( xcyd2xy2ph(n q+* 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 i 1;d 73s/;yj8ovu* yfmjzbcr vs 32 cm long between fixed points with a fundamental frequency of 440 Hz and a mass per unit length of 3b1ms;*u d7yc zv8j/f orjy ;v$6.1 \times10^{-4 }$ 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 tube* t+ no.yq(lxvb sw64c 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 tv *ycq x.oslwn4t +6(bhe 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 stb f :h4/+o ,2yfdrihwhring 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 i/ owhb:rff,d 4+yh2hstring if it is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one full loop (0q* gfxe1w;zb 2oif-p7(wrcdmcl5 9 a $\frac{1}{2}\lambda$) 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 sourcemiqbl+g fy9l y62aw9)s. 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 than the other. Whata+lqm )f9 gwib9ly 62y is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles /(xvrjb81ppc 7ri hy,. One train is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequency wh x1vicbrjp/78 , (hypren the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it apprredb5yjd lnbb rw6n3(6(5x5x oaches you is 538 Hz. After it passes (bbxdn65bjr rwyle5dxn5(36 you, its frequency is measured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimat-2 spb +un fdb/ek-3tre the speed of cars just by listening to the difference in pitch of s-db 2rept3/k b+fnu-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. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11,: 0pj 9bk ni*uo1pvok Hz. The shorter one is 2.40 m long. How long is theo bkk* 9poivnp, :uj10 other?    m

Two loudspeakers are at opposite ends of a railroad car as it moves past a s haw5).co:ow mtationary 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) hcm a.:h 5w)owoe 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 aorta is normally about 0.32 m/s vnfk ,hh)pu+ ,what beat frequency would you expv,ku +hfp),h nect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth :bh.,eu/dqel at speed 6.5 m/s while the moth is flying toward the bat at speed 5 m/s The ed/ bq,he. u:lbat 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 o e e;epe:mu odfb,j.3c*py04tf high frequency sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp returns before t,4eetjyu 3c0 *e b;.odmp:pe fhe next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) wxtp * /b 2pd6jrr )pdvld yup1o.l0,w+as once used to send signals from one Alpine village to another. Since lower f vrdw/0pdllbro*pd+u,x y1 jt6p).2p requency 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 ben3guycc 67rso:e(b i1 compromised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nod3( 16csb yneg:ri 7ouces. 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 demonstra 7x zid5bxqq++tion, called “singing rods,” 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 sound. For a 90-cm-loz7bqd+qx+i5x ng 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 a frequency o7/k5wfu+ex4j jm b8otf aboutfe85m/ 7ubjotx j4kw+ 1000 Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on the groun4kr tg96qq9 9mq)xtvpas +6km d hears the sonic boom 1.5 min after the plane passes directly overhead. What is the plane’s altk4v tm6r9 gp+ q6mqs9 qak9xt)itude?    $ \times10^{4 }$ m

  The wake of a speedboat is q w7r6 1xbw5pvof0kb tg66vz/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