What is the evidence that sound travels as a wav*wh6 0+* fbshprn :qjve?

What is the evidence that sound is a form of eneqc l1v7p wng/uxd5 .k2 l2sn9jrgy?

Children sometimes play with a homemade “telephone” by attaching a stringvij6ppadh1 oiwt-2 3) to the bottoms of two papita1 vho- )dw p63i2pjer 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 frequenf(hz.9b v4on5cd44,g uvpim gcy or waveuv4fo d45 gzbgcm pi9(.n4,hvlength to change?

What evidence can you gic mg7e4o1oh mrh)no k6)fi55ove that the speed of sound in air does not depend signifc) 5e651i 4k mrno mhgo)7ofohicantly on frequency?

The voice of a person who has ink o(+4 1t i.ccos4kxdahaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch uobw5n s5*aan x1lp 20of organ pipes?

Explain how a tube might be used as a filter to re2,1d5n xdsn ohduce the amplitude of sounds in various frn x2d dh51n,soequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer t3e 4m-7na ztvuz 8e(q0uekl)cogether as you move up the fingerbqa) lu kn3zctv0e4m (uez- 7e8oard toward the bridge?

A noisy truck approaches you from behind a buildi)nv bhe+6 0. thdgb4cf*gc hhmbkk9 9)ng. Initially you hear it but cannot see it. When it emerges and you dohg 9.0h6))h+*4ed bnbmkbkh ccvft9g 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 “intvpb y1i( gg2,rej9u-i8n1a fmerference in space,” whereas beats can be said to be due to “interference ini 9mvj ba -i 1gy,f1g(8purne2 time.” Explain.

In Fig. 12–16, if the frequency of the spl1nt ba4;kvj1jgr )d1eakers were lowered, would the points D and C (whe1rk1ld;j)jga b1 n4 vtre destructive and constructive interference occur) move farther apart or closer together?

Traditional methods z9 o aq5y9w4tpof protecting the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block a4oyp9w 5tq9z 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 reaching the ears?

Consider the two waves sh,m j d/nlnzs*x ndztau8uo.rr:z9 3 y;w0 79ndown in Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In whic3jlzz rndun9:wt*7o0 rz xd98/ d sym ;nan.u,h 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 direc .l(b-wvhr;9b*isx w ur +y-pwtion, with the same velocity? Explairw.h xilb sv-bw* +;u(9wry p-n.

If a wind is blowing, will this alter the frequency8u q 7uo3j /lg,.ojhks of the sound heard by a person at rest with respect to the source? Is the wavelength or velocity changjh7q3, / luo.gkso ju8ed?

Figure 12–32 shows various positions of aq4qhkbwj/pc x 9d 06f (k7xzirjse20-a 96cq i child in motion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which positiowq/( 9ze -rbdcx2i0 sq ipf6q jk6k7xh49a0cjn, 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 afr)v ay:k 8xaa-o)dr / lake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echoafxavr -a/ )8ro)y :kd 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 waterline-(9: v n fzuzy,:xkk7rgjp1bn. 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 point? Assume the speed of sound in seawater is 156xyu9b znzp n fkj:v7-,1gr(: k0 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengthfq3/iexad od;+el6/k 8ux6d x 2zvs)fs 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 on a foggy day. Wi./ vym : ap9kisz*5xkkthout wari./k:za k9*5xkv smypning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splascx1l7j y9n5csh it makes when striking the water below is heard 3.5 s later. How hx59s cn1cjy 7ligh is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the c*pgzii,e0wa2qqide.8 / g0k )e1qs rxoncrete pavement. A moment later two sounds are heard from the 8 s,1qk*q we0dir2i0ga ziqx)/e.e g pimpact: 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 over one mile y9zkv s8(l :ofof distance by the “5-second rule” for estimating the distance from a ll9 k8 v:f(oyzsightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at dxm*ta 65ik1 fbth44 xthe 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 s yy qs3g1y,v,m6 )s.,d/ easmds1 uyyround whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fireqdr+r9+il8c ggk l*9hxfk4 ;fd simultaneously at a certain place, what will be the sound level if only one is exploded? [Hfg +cr krdkqlx 9gh+8f;il* 94int: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplacfyp-xxr86 w55g + wx,p)4lkca 0cor sne with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB 5-g,0)xrr5a6px48 co ywlp csfcw+kx’s.]    dB

  A cassette player is saide1nq*f2 (w6 6avxnsug to have a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and nnwvu2(6g6fe *xa 1sqthe background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in normal conversa907c hpn q:omk;c9oqx tion. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the mout oqkqonm:90chpx7;9 ch. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave strikes an eardrum w ( j .kdpvuh)7)8q9oitcc,gvh hose 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, whileyqfc.9t: li s:wc)k4a 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 loudspeaker connswi t4.):aqlc:9 fkycected 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 melc 04794o ola-rsed- vnyyg)eter registered 130 dB when placed 2.8 m in front of a loudspeaker ong0nre7 ly94v4 -ls)oedya c-o 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.c j1.am*b0nrn What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: *na c.br mn10jSee Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will t3j 1 : (o.+:jewnpu/xhwjipelhe intensity increase? Increase by :j u(1o/ehw:i+ lxjp jwne.3p a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudeyh- 4ns dqri/wv2cin oq8z/7 206grkcs, but one has twice the frequency oh/-n igok8crqws qy v472 n/ r6zdci02f the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that corresponds tor sf3a6.9ett v a displacement amplitude of vibrating air molecules ot6rae39s.f vt f 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level t5xd19xaa(,4f qxsguj42 z dnto seem as loud as a 100-Hz tone that has a 50-dB sound level? (See,j9 d45g qxdsa4a2tx(fxzun1 Fig. 12–6.)    dB

What are the lowest and highest frequencies that an e i (ghmgr,n gffbb9).9i *6tcjar can detect when the sound level ishf(, r igm9b9bjg 6t.)f g*cni 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound level 0c5y u1dbty.4r3mlavs. What is the ratio of highest to lowest intensiucmv r4yyad0t 51b.3l ty at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violisy+ln bf :13pjn has a fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string +1:j pyl3 sfbnbe placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first three audi, elzjv3yiw+y ;,7imtble overtones if m, j+iy,le ;iwy3t7vzthe pipe is
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you expect from blowinkh0 r 7i/ej3sbz0hn+rm9x9jj g across the top of an empty soda bottle that is 18 cm deep, if you assje+0 9nsb703kri9x/jmr h z jhumed 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 orgw*h no3hww - +*eb5quban with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the rang5* qheh buw3*wwo-+bn e of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string8/k1fg/yc+mk ccouzc , n-n1g has a frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of onom ucnczg1cgy / -8fc/n+ k1k,ly 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play.3 w;w me vp:o6gktd9g E above middle C (330ketd9o36p.gw;:mv g w Hz).
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that emits middle C (262 Hzjw5-nd/e3ap1-w prg4cfz n-k) when the temperatu5p pd-wf-a-c 1z4jn3egw /kn rre 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 20nl+i-dmm*9( g mp4 7tqi2q 9cw6rnxfk $^{\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 shoulw4eq5t vnl- 1hd the hole be that must be uncovered to play D at1e -hwv45lqnbove 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 resonate2e li bx4xg0+ajz 78px at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or aex g+bpi78x jl x0a4z2 closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m g;m *4g,. fzpuvbzju o;wub/ *long is open at both ends. It resonates at two successive harmonics of frequencies 2gg;j;ufb*m z b./puuv4,zw o*75 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 m9wt 5w u yq; dxz-.zf;uw6kq:$^{\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 ran:el +z.)1by 9l kmmivj)bq-nsge for a 2.14-m-long organ pipe at 20 lv)mez9. b :1ln+ sbik-jm)qy$^{\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 tkwmg.x l4-f7and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. Wml 7fw-4kxt .ghat is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to adjust t ww 1mw31x;0-q(crf as7 rfzrawo strings, one of whic1a 1w fwmxr(7cr 3;zqfars0w-h is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262q5 ajb7*cro k5 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while another (branr:1 gpc/yagw4 vv1nl5d X) operates at an unknown frequency. If neither whistle can be heyc lnr 1wv:/5v1pgg4aard 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 a mbqd z*k(:q g.*:mzpwhen sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning mzaq:z.d:*qg m pbk( *fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequ.)spjs6u vk4 aency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency . 6 k)svjpu4saheard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play middle C (+qx i(4wx0ur * mmmhb5262 Hz), but one is at 5.0°C+04xu rw*ihb5 m(mxqm and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork b: ).skji 9 2twgdc - 9ofic0;(yx*s0odekrubB 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 areob . b9sr9jkcd)y e;-2is:oicu fk 0*0 gxwd(t 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 /cl-c ;yl:lzhstands 3.00 m from one speaker and 3lhzlcy;/ -: cl.50 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, b2m;t s4x, svqgut a piano tuner hears three beats every 2.0 s when4 2;vtq,sgs xm they are played together. (a) If one is vibrating at 132 Hz, what must be the frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound of wavelengths 2.64 m and 48nx a9znj o 00tiga4c2.76 m in air. How many beats per8axcna94 zgj ont 04i0 second will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’ wk6scnoe;g/.s siren is 1550 Hz when at rest. What frequency do you doe gw/n;s.6 kcetect 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 yp-o+,co/ npy a fire engine whose siren emits at 1550 Hz moves at a speed of 32 m -p opoc/yy+n,/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving townj z ud -3-z xo+/ko9r58nz/yk uosxa:ard you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they clo a zz-od:xu-nxuo rn3yzs8+k5 /jo /k9se? $f'_{source\,movine}$    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 frequencmp.nodvba 2 e)ido* *:2bvf;sq8;ik hy horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is*)fe8 .2mb op*bh;vsnia d q 2o;iv:dk the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz andme z; b2bynfe 84os21z receives them returned from an object moving directly away frz2b4 mnb8 s2zfeo;1e yom 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/jwcrygk. ,+d emits an ultrasonic sound wave with frequency 3, .grcy w/jd+k0.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiyx; 5ifo.kf xx 0:9odlments, 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 freod;. x9 iox0 fyl5xkf:quency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves tx uk+nwk/1f 4mo measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in humaknx ufw+41mk/ n 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 ultrasonic waves of fz9hzhj,wpj k r.k192a.l yl9 vrequency $2.25 \times10^{ 6}$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. Whl4j5i ubn mh8)en the wind velocity is 12 m/s from the north, what frequency will obsem8bl)iu4j h5 nrvers 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 igjwb3+67m* lo2meymj*;oxc:ha ma: bf 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 spb u4l1*x/igxaeed of sound is 310 m/s (a) What is the an1x4ux/al*b gi gle the shock 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 of a planet whez ma 6b2wg;fh5re the speed of sound is only abm5 af;gz bwh62out 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 8ph4ja. ;mxf(i 500 m/s strikes the ocean. Determine the shock wave angle it produa ;(pi4xjfhm .ces
(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 vg)vo2z3 a;k u$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and sffo1 e e-tbefq59:u*w 2 ku5fgee a plane exactly 1.5 km 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 of5f-ftqe29euew 5g kuf 1*:ofb 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 jh+w :ke,h9vfaw/h z j/f*yf8 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*+k ,hwjywjhf8f / a9: h/vfez work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in f(k3ef i*gz 8rdbi*v s ffa.6(the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphy nj85ay7s3 f4hu/ zstony. It consists of many plastic pipes of various lengthsn3j57/4 sshytf8yauz , 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 fro em5d5d lop:*tm a person makes a sound close to the threshold of human hearing (0 dB)e5*lm :5tdpdo . What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-dB sound la7cj4j:chb- 7ug 3 tbo0wwl:are heard simuo 7wu -bch0j blw::7l3 g4cajtltaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 dB. Wha(/ l49pjyns rtt is the acoustic power output (W) of the speaker, assuming it radiates equally in all direcln(9t y4srj/ptions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The power output dr qkt11be9fg(p ops by 10 dB at 15 kHz. What is the power ouq(p t9 k1geb1ftput in watts at 15 kHz?    dB

  Workers around jet aircraft ty t/q4wq )7xi,y1 znpkkpically wear protective devices over their ears. 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 itxzpy7w/kn41,qqk )cm. What would be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, the gain,(4 85faq)x q oz8motlx $\beta$ 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 mw1 /j q3s 6fjoebp40na frequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long bet1*jw*y o+epku sdi9; o+e9neg ween fixed points with a fundamental frequency of 440 Hz and a mass pegy ;k919+ deo+ ein spwjuo*e*r unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration above a vertical /.)jsnmq-p( 3x s dziwopen 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 wate s)n3m( qw.psd-zix/jr 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 ij/lq:e n2z 3rmass 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 innq2jz il :3/er the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to reson z3e8szxxdy 34ate 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 500q4.9lu0iw6slm ad3fhunmm 2trt d)2 8–1000-Hz range coming from two sources. The sound is loudest at rdmulhl3a8 im9mt2 . s nt)0w4d6 qfu2points equidistant from the two sources. To determine exactly what the frequency is, the person moves about and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The conductor on w p4szu(0hpsacc,b.7t;5 xo kthe stationary train hears a 3.0-Hz beat frequency wh pb4utc 7aphw ,co(0s;x.sz5ken the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it aprewxbm71q pjr/5f t ,vbb0c)8proaches you is 538 Hz. After it passes you, its freque qr8em1b fwb5t,rc)v70bxjp /ncy is measured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed ovb y7t w(,a+vpf cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain cbwyp,a7+tv v(ar 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 j+i2 ogefa p+ f43s,z5ow,b ydmr-s 3xbeat frequency of 11 Hz. The shorter one is 2.40 m long. How long ism4yp-3,eb,sd5a 3grwfo+zj x if s+o2 the other?    m

Two loudspeakers are at opposite ends of a railroad car as it moves past a stke66 r /l9posyationary 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 66yp/o9rsle k 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 flya*c uzn 3on+)ow in the aorta is normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from the red blood cells? Assucan zyo+n3)u *me 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/rzqr5 1qp.tgagg y q sihd v+a+yb.(an6+d32)s while the moth is flying toward 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 reflects off the mpbqrti +gyvqds6a ra. +h.q3g+a12dyng)5z(oth?    kHz

  A bat emits a series of high freq6n+vr 4;a pmjwuency sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How famj; 6vrwn4a+p r away can the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to se pc,9jw -.ga1hsz m 0axk24dppq*p0xcnd signals from one Alpine village to another. Since lower frequency sounxc2zp1qxac akp,-pm.*49jsp 0d 0wgh ds 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 compromised by the presence of standox1ztpr mp+3 4wad 9g1tpbp+8md ):nfing waves, which can cause acoustic “dead sam g+m4p 3d p)1 n8+pofxt9pz tw1d:rbpots” 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 4rm5 q u0dui1w*n*by.1adn ptrods,” involves a long, slender aluminum rod held in the hand near theu* prqi 1 n5b4.0 dd*anmwtuy1 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-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 heaj30v+9mol jnxo++h0xuz- r euyhb7g4ring for the human ear at a frequency of about 1000ejz94h3n j0vogux-o+xu ymr0+ h+l 7b 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 afq(6 fp ebh.42kgvb:nt Mach 2.0. An observer on the ground hears the sonic boom 1.5 min after the plane passe4v:.fe6bh b2f qg pk(ns directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboar *1nty d21 0ko*eeixvt 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