What is the evidence that souj:vy eey.ev (od4gqe *4r: .qond travels as a wave?

What is the evidence that sound6g j6fp(tug wxmwi(1z*g:2bo is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a string to thewt2+buu zk x 1nw;dc8 xbx1*x8 bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from wb1 kx8xt28cxbx;u nu dz+ w*1one cup to the other.

When a sound wave passes from air into water, do you expect the frequency or )oou m(1qxmv(q +r4 rewavrmvm4(+ oxouq1qe() relength to change?

What evidence can you give that the speed of sound in ai + zc2otcgsv0o, dcb -;vum,rf/ f9fn4r does not depend significantly on frdf/ rmnfc4vc vo,,+;9obcs2g0 tfu-z equency?

The voice of a person who has inhaled helium sounds veh,k/ n1n:1hswwv ;5epk+ f pukn4 w0kiry high-pitched. Why?

How will the air temperatylxq7s:( tll0+ fc8p qure in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amzdnl 1-f .m-vnxva 2vgx -8-jbplitude of sounds in various -ndvfgv2v n.bm-za8--l1xj x frequency ranges. (An example is a car muffler.)

Why are the frets on a guitarzf0w.,qs2 bqi (Fig. 12–30) spaced closer together as you move up the fingerboard tow wf qsiq,.0zb2ard the bridge?

A noisy truck approaches you from behind a building. Initiag3r+v x:lb tqtud)b011cg-zc j,r. zylly you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighcqlr3 b10rgj) zbvg., y-1+zutxtcd:ter” — 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 spac x*,):k- p8(jrhlwkvgb4xsg3t wm m o*e,” whereas beats can be said to be dbsr:*pkwx gokw lm8vg)x (3mhtj-,4 *ue to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers r -tu1 y7clf,;vfsot4, z(yxk were lowered, would the points D and C (where destructive and constructive interferen74uo s;zyt(f,, -vy lrxtf1kcce occur) move farther apart or closer together?

Traditional methods of protecting the hearfm) 1ctv:ax2* l/xjbjing 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 levels r1j 2*m )f/jcxl: baxtveaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can(6(ob*7 5 v usvqmmfhx be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farth 7sm(*vf bohvuq5mx 6(er apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the sw9l3uvqt/em ab (k 7.fpivc;; ource and observer move in the same direction, with thlvaf u.e37;cw(t9kv/ bpmq;i e same velocity? Explain.

If a wind is blowing, will this alter the frequency of theb8c-brb zzbg656+c y5s b l*he sound heard by a person at rest with respec8g-bh s6c br5bzey *6zbbl5c+t to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. Agtk/ 65.ru4tyee mt b6 monitor is blowing a whistle in front of the child on the ground. At which posit 6t.eyerb/m ttu6kg45ion, 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 echo of her shout u/w i9c5q0x5hn wttp/ gf* :jbreflected by a cliff at the far end5 xg0ip5t:9 /t/hwnb* fjquc w of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship * hy7t-j.jm-h ,qpnpf just below the waterline. 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 hpptyj-7., m*jq f- hnis 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air 2)h+ ls29 wfawrj bgt.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 30szh,hw yo/zdrifting 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). How much time elapses before the backfire is heard (a) by the fish z/ 0hsohyw,z3,    s (b) by the fishermen?    s

  A stone is dropped from the to1i4/ yw o u3kfkq,dny4p of a cliff. The splash it makes when striking the water below is heard 3.5 knkw44y/3u 1,y fdqios later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the conwjv;:pctu;gk l;s9+ c ;yvy 8hf1qi5hcrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the ;h1v;tf lcy; :hq5kwcpy u g+ vs9;i8jimpact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent yy. 2n+ )iwvzudv5q8 derror made over one mile of distance by the “5-second rule” for estimating the dist +5wzyv.8 uqv d)d2yniance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 120 dd.)ni qugl1 ahn fr18uimh:*tz * (3osB?    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 whosyw ig5 , w ro-j29,:zg(xqcbcze intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level 8u-u /y pdn.bfof 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’s.] unp /.yf-d8ub    dB

  A person standing a ce.szje z0jogmm 328(yxrtain distance from an airplane 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 captai 8ozmejm x.j sg(y2z03n shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have usvz17g: c+:rgr z0nd3x+ wrt-k yp.u a signal-to-noise ratio of 58 dB, whereas for a CD playec.s-3::r k1gp7ndz uruw++tgz ry v x0r it is 95 dB. What 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 speaking in normap2r 0:qmwopnwue 9 4m+i9 c-xwl conversation. Use Table 12–2. Assume the sound spreadsmw9pp+wumq -o: 0n ri w94x2ec roughly uniformly over a sphere centered on the mouth. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave strikr j6ppmzz7n7jq :b /l7es 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 250 W, while the more mode+h ag*s +b aqwws*h)6wnldi,z7bf im (h 07yq*st 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 f* wabdz7)6 qa+7qhswgily(hb s w,0 *m*ni h+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 plvvmkwbv fd4 d8 ,n6l/w:c 5gh9aced 2.8 m in front of a loudspeakerh d6dv8b v,l5vcm f 4g/kn9:ww 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 dete 6p 7srku, -p*bodgwu.ct a difference in sound level of 2.0 dB. What is the ratio of the amplg skdubo-p.pr ,w76 *uitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tr / jx mvgc33)e6iznm2pipled, (a) by what factor will the intensity increase? Increase by a faiz3v/)g6jp c2mmx3ne ctor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one ha/v+p3w 9 uoelzs twice the frequency of the other. What is t9/+p luw 3evozhe ratio of their intensities?   

  What would be the sound level (in dB) of a sound wav jf 8tg;r+ yu anz,(rcwlx79;ee in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 300 H ( j78zueta 9ngr;x crwl+fy;,z?    dB

  A 6000-Hz tone must have what sound le0jazw.upk8)y gv 3x f+c9qcz:j2ym v:vel to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. 12–6.)jg:m+qc k .9fxcayp u vy20):zw3 z8vj    dB

What are the lowest and highest frequencies that an ear can detect when t3 nsl1qb)u+d-4 ezjwy1iy p1jhe sound level is 30 dB? (See Fig. 12–6.) 3s+11dpzni41 q- u jjwly)bey

  Your auditory system can accommodate a hughniyaqjb0 xbus)2.625n ew3 6rx( ekpe range of sound levels. What is the ratio qbns.ihe 2rjwp(0kbexa 5 2xu 6 3)6ynof 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 Hz. The length o6q k(o s9z :n,jvgnf5wf the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be plkw gsz9fn,: 5v6jqno (aced?    N

  An organ pipe is 112 cm long. What are th7z4h b 4o wgpi.t 1r7*zgc2zlh3/ topfe fundamental and first three audible ovel /3tf4 o147.iwg27 pht*hzbopzzgcrrtones 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 frequenph2 3f7nm 0cqd/)dg :cgw/wyrcy would you expect from blowing across the top of an empty soda bd:f0/rcn q/gpy g3)m hwdwc72ottle 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 pipes spanning the ranggq d4ep:ulamb(,/7gg e of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipesg:gqale 4, /mp7bdu(g required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has8lzovw)hke gf* u)b* 2 a frequency of 540 Hz as its third harmonic. What will be its fundament8 h2fzb k )ueow*l)g*val frequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m lon wbjdlth/7l*l/.(2+ um vfltmg and is tuned to play E above middle C (330 Hz)udwflb/ljhm *(7 t2+m lv .tl/.
(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 i1+9kaw qs7*;eic,3un ict bnorgan pipe that emits middle C (262 Hz) when the temperature qbac7ii*wk9iencs ; 31u,t+nis 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 z )*b72tic1r: azdrgn 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Example 12–10 should th z+jch7ft:(m(anc 9u be hole be that must be uncovered to play D above middle C(a ut:7cm9c zhfj(+ nb at 294 Hz?    m

  (a) At T = 20 $^{\circ} $C how long must an open organ pipe be to have a fundamental frequency of 294 Hz?    m
(b) If this pipe is filled with helium, what is its fundamental frequency?   Hz

  A particular organ pipe can resonate at 264 Hz, 440 Hzes eaf8d,i ,5k, and 616 Hz, but not at any other frequenci 8fee5,kad ,ises in between. (a) Show why this is an open or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is opeyd+dd0)4ul16 vl lenrl 1b5e hn at both ends. It resonates at two successive harmonics of frequencies 275 Hz and 330 Hz. l5dlehe)1dbd41v lnr ul y 0+6What 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 sa *7g +abglf*y6; k b;tkowx0$^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are present within the audible range for a 2.14-m-long orgas -qkk lagx ,8hf3);fvn pipek,l 3vxf)hag;sf-q8 k at 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 ope6ba1z ex4)j.a9vhuqxn 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 thea4ue ax ).vb6q zxj91h 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 tr2 x f5 )0c9aymkdgp5.8*ob sq8ejciq qying to adjust two strings, one of which is sounding 440 Hz. How far off i 8gf2)kcexjbam55*8p d qqisqyo9.c 0n frequency is the other string? ±    Hz

  What is the beat frequency if middle C (26/90sel iy2 3r/zm ;ti gey5uzm d6bek/2 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 anotherl)gs go8wdt*k1 wf38y (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when plaf1dwkol) ywtg8 s8g *3yed 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 w5 :15.bfhbhy re0rjjoith a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequen.yhh5or rejb0bj1 :f 5cy of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 20o 3,qn4i foos94 Hz. The tension in one string is theqoo0o 4,sn3fi n decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try tvc ,fw+w-se /n d3t*cjo play middle C (262 Hz), but one is at 5.f3wv /te,dwnjc+*s - c0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. x*:-+ b:gj7jgqm a/fpte wz0aFork B has a frequency of 441 Hz; when A and B are sounded together, a bejmz/0:eg bwjf:a* 7tx+ apg-q at 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?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A pet emcd6r+4 (mhrson stands 3.00 m from one speaker and 3.50 m from thehmr c4tde(+m 6 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 98c gt5 8-tkwzvmn8p fHz, but a piano tuner hears thr59nf c pt8 m-kgtvw8z8ee beats every 2.0 s when 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 2.76 m in air. How many bevv 7vt;0lvn3 omcp.,np+9nlz ats per second will be heard? (As pto3,l.0zvl7v vnnv c ;mn9p+sume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of xw gj;pu5j)+ ia certain fire engine’s siren is 1550 Hz when at rest. What frequen5wxu+ ;jg ipj)cy do you detect if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a firu r:1r(5x z :h:-tyhlub s/u4ax;gup we engine whose siren ebx;xu:5 wt1s -( :ugzu4pua /hy:lrhrmits at 1550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency ifj ;6+wcomt *n j0..40rm undqxvg 0lsjip8kc. 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 exactly the same? Are they .gcnpc8vx 06irdmm j ;s*o.qujt .wljn4+k0 0close? $f'_{source\,movine}$    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 frep)u k5muj t1oy:9p 40*fdmrhgc 22ujrquency horn. When one is at rest and the other iru:p5k0tg yj phum4jrd*c) f22o u1m9s 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 ultrasonic sound waves at 50.0 kHz and receives them y h8j,fuwb* 2m* *teq3jmfo6oi.d+gh returned from an object moving directly away from it at 25 *mt. ,8 qdfji* ho*o6fbh+ug 2wymj3em/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s yts fl(/ )hlwt8q 09yucb.4b oAs it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz/)oyflb cb(0t s48 lh9y.uqwt . What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Dopple8a+ x2vp*umi ar experiments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and*aaxp vm8+u2 i 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 usec/ msh l angl37 kvxl/w7z:q-5s ultrasound waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg artq3h7a:svw ln gkzxl7/ /m-5 cleries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves m6 k(g.a tu igsw --ahu5,v6b cg/jgc: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 emit*:(uy yd.b.n tsgni1ns sound of frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are located, ayns(* nt:uyg .bdi .1nt rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if its speed atho 9 ws5j, b0jxofevyzku/752db p(5a 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 speqadvg+.,9vwabz1p 3k ed of sound is 310 m/s (a) What is z p.3gbqa9 w+1vavk,dthe angle 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 atmosph1 dwo. yci.bw7ere of a planet where the speed of sound is only about 35 m/1wbd.woyi7 .cs
(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 vem c.y.l .kge*i2lq ubs,e7. the ocean. Determine the shock wave angle it prvsmeie lb2.7 lgcku e.,y.q .*oduces
(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 qshb/)oel pune7 8 .7o$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a plane exactly 1.5 km above n8f:ppfmoa- 1the ground flying faster than the speed of p 1-o8 mfnap:fsound. By the time you hear the sonic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 12–34. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device that sends 20,000-,-ev(mab3sia (gi3dxd2ppm+v(lb i 6 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 s(i (pxvdeb6l2d piv3,3abm ma-g+i( the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there ikxng.c)t2t( wg 1s6;e5 eelhjn the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a disj h 8 tza.mydilau380v)n0xx/play called a sewer pipe symphony. It consists of many plastic pipes of various lengths, which are opez8a0x 3y/j 0vmh)aulnid.8xtn 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 t8jvjpka.): ez o the threshold of human hearinp). ajkj:8 evzg (0 dB). What will be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB souncjpi 3 7.o 7)hd:nbb3 fdhis2(v4lwtrd and an 87-dB sound are heard simultaneously?4 )t.jdchb 23irfn7ob7sp:d hwli 3v (    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is y1gr ,-p6kghakh:khjf,i ) /o105 dB. What is the acoustic power output (W) of the speaker, assuming it radiate/fgoj1kh- h ir:hka6y ) g,k,ps equally in all directions?    W

  A stereo amplifier is rated at 150 W output at 1000 Hz. The power output dropsy k7km 7,dyms: by 10 dB at 15 kHz. What is the power outpsy k m7my:,7dkut in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices ovstw q6yqwdf dpo:0y 1 q3or;08er 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 cm. What wy 0oo8sq36;wqwr 0ytd1: pdf qould 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;;5aa2k hqou:ax dg:3s y9 yld gain, $\beta$ in decibels is defined as
$\beta$ = 10log($\frac{P_{out}}{P_{in}}$)
where $P_{in}$ is the power input to the system and $P_{out}$ is the power output. A particular stereo amplifier puts out 100 W of power for an input of 1 mW. What is its gain in dB?   dB

  Each string on a violin is tuned to a frequency 1i9hy gbk-9c s-e0zo1u$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long between fgpwdfhre j*+3-sp a 8fg0t 1tux1z7 2zixed points with a fundamental frequency of 440 Hz and z*-1 8azxpt3 wt+27j0rp1fuhefsd g ga mass per unit length of $6.1 \times10^{-4 }$ kg/m
(a) What are the wave speed and tension in the string?    $ \times10^{2 }$ m/s    N
(b) What is the length of the tube of a simple wind instrument (say, an organ pipe) closed at one end whose fundamental is also 440 Hz if the speed of sound is in air?    m
(c) What is the frequency of the first overtone of each instrument?   Hz    Hz

  A tuning fork is set into vibration aboveo55s3s t;zg g yfu5h0x a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening tofy zstx;o53s0 h5u g5g 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 *ucr ovi. r3-t8b5kmr8x byc6one end and also 75 cm long. How much tension should be in the string if it is to pc85ivrc*b y- u6krb t3or 8xm.roduce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was 5 ;mh1)5v)a4/hcuuz jpcbe)( qtv+ iwol(fji observed to resonate 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 4rybyd mp/7qs zp qt0(/) 1exqin the 500–1000-Hz range coming from two sources. The sou7q4rye/(y)t1s pp 0mxq/ dqb znd 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. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stan/7mvj tv bs9;q 5nq-f;oln;xtionary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approach; b5f-nl 7 x s/;vntoqn;vq9mjes. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approaches youd 8z,p nt8qo)j is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving (assum,q o8njd8p)tze constant velocity)?    m/s

  At a race track, you can a0apn-:vj rpzx9 , j5destimate the speed of cars just by listening to the difference in pitch of the engine noise between approaching and receding ,n0j 5xrap9zp:ja -vdcars. 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, soundfeu; te m41dugu :.j4sing together, produce a beat frequency of 11 Hz. The shorter one is 2.40 m long. How long is the1 gm4 de:s.uufj;u 4et other?    m

Two loudspeakers are at opposite ends of a railroad car as it mo6xsp1.-g9m3 b ext*r u p*xw zb 6lt4;qw/pobaves 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 speakebpw*;6xtxlp os 19 ztga e6wbm* pqxb.3ru -4/rs after they have passed him, at C?

  If the velocity of blo25x1iy7 wtutrod flow 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? Assume that the waves travel with a spitytw51x2 ru7 eed 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 k r0ku2ngi lx aingh2pi 96)*cog)3( +ayu3l dis 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 reflectsao 3cl+)gu3ak)( i6y9gxi22l0k gn i*dhu pnr off the moth?    kHz

  A bat emits a series of high frequency sound pulsei:y18g- roy9ifppr*x s 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 de8x 1frgioypip ry:-9 *tected 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 send signals f*oq(jk 9qc d+gq zwea* dvg, mtl)3+x:rom one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one k *evd t,d3*mlq9ox:j aq gg+cwz+)q(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 sta4t z.wolygn;sv8kx)d 1-v;ph nding waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0zw p )8tn1ox;k.ylhd4-vs;v g 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,” invol fvyuux xg:,9s 4*ib1hves a long, slender aluminum rod held in the hand near the rod’s muh *1bv4,9fxs g:iyxuidpoint. 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 hearing for the humandr9dn :ws3f knh/qk4r78u o9w ear at a frequency of abo4h7sdk fw9/wr nn r:ku38oq9d 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 dbn +x5:ntn*n at Mach 2.0. An observer on the ground hears the sonic boom 1.5 min after the plane p n x:b*n+d5nntasses directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedbo/ln, :b i0cczuat 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