What is the evidence that sound travels as zi:bh(h6 vw dxexa56 v( x7uv4x.) xxba wave?

What is the evidence thp- op zhn7h,k.at sound is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a strin g mng*gw g31yy*9fv0lg to the bottoms of two paper cugf0lgynym 9wg* 1* g3vps. 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 f( zw+ 9z4- 3os,l)dnc.s8osfh ti yqqtrequency or wavelength to change?s-,qot)zl 4hss +zd .oqn9ic 8w( tyf3

What evidence can you give that the speed of sound in air b- aq; u9cima2u)gd*ddoes not depend significan)i2 gab- cuduq9m a;*dtly on frequency?

The voice of a person who has inhaled helium sounds very high-pitched. Why?, 26x)nf.o zjz y:vfzx

How will the air temperature in a room affect the pit e zf)uel5f0t1ch of organ pipes?

Explain how a tube might be use.*. +v:lg5 ,am riruyh4iooc rd as a filter to reduce the amplitude of sounds in various frequency ranges. (An,uo*r+ylr ar 5i: vcgmi h.4o. example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you move upgs vz 3xopfv:6q gr iwlx:)g4hg)z+ /) the fingerboard toward the br:xl)/+:vx qp o)hi )g6g4wvrg zs 3zgfidge?

A noisy truck approaches you from behir.an9e2y7gk p dx1+i gnd a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on 1x pera2+.d ky7gnig 9diffraction.]

Standing waves can be jrj zh4z/g13p w):2j.zkc q( q+hzksh said to be due to “interference in space,” whereas beats can be said to be duz+jkgsj4j wq h p/q.k 1)3h czz(:hrz2e to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the point dj;h*szn vw ) 0l/fvjm98v:d4ejgdi;s D and C (where destructive and constructive interference occur) move farther apart or closer 9;l;j niddjzdm:84ehfw/s*jv 0)vvgtogether?

Traditional methods of protecting thew( km o0 lswm)y9)tmh8 hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a whm9k l y )(so)0t8wmmdevice 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 shq j;+ *x7)czh0e)lynso ff7 nwown in Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequc)q+*7j fhznlfns)0w7yo;xe encies, 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 rhwie9vh6 ti(e )60 xeif the source and observer move in the same direction, with v irhhe 06(wt6e9)xiethe same velocity? Explain.

If a wind is blowing, will this alter the frequency of 7/ 4od+oygl9u7 fq im.w8buvu the sound heard by a person at rest with r w/iu9u8govouf m q4.7 l+7bdyespect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various position apvafj)r 9j3tve 5l80s of a child in motion on a swing. A monitor is blowing a whistle in front of the )avvpe f 9r8tajl5 3j0child on the ground. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the 5.f r1 cvxoy/hvvhow-; gh5r k*-xyt9 length of a lake by listening for the echo of her shout reflected by a cliff at the far kt 9;1/.vorox*gfy wy-5vhv5xrch- hend of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He hear,ip h-ub7;p kb 69urup-dxgv1s the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point?pvp7p9,x r-bbk di6;1 -gu uuh 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 wavelengthgfi+8uf o.aa0y n*a m 28reeb.s 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. W8k::vu c4g;3hva6- geptc 0oqah- kjvithout warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (j-kh e phtvauoa4vc g-:c0g8k;3q v:6 a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash icy;( lki+lj 7.kqvez/t makes when striking the water below is heard 3.5 s later. How high jkq;( ki/z+cl. y7levis the cliff?    m

  A person, with his ear to theruk99 1vybvnga11 -iyx-i3bc ground, 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 concrete, and they are 1.1 s apart. How far away did th919-ik vxg3yb1- nirb 1yavcue impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent ewqj ;.fqz.px z0g3rs7z* 3pzx rror made over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if tx.0xzs zfpzq.pg3wjzrq 3*7;he temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound y,pcm6* i roh lgyf)z6-p3 c)yat 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 sounde-v0u hg crk)c./) bdz whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a souniwsp5-g )fg+, 3jt tjsd level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one 5gj,-pi3gw ) s+ttjsf is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distai.93lpq c5k6zw21nu+ u)tif fsbf0p o:e a zg(nce 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 experien z.loep9: )iuqt01w53 sibf+ n(2fgfkzp6 auc ce 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-noi(lf6h 4njzrb.ep*c3 hse ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities ob4ejrh6 f.hz3lp (cn* f 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 normal converc1;2 :j0c b .nbioo i11lo(r)n ztxpsvsation. Use Table 12–2. Assume the sound spreads rou);0c1.ti:vbz(l2jino xn oosc1r1 p bghly 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 strikes an eardr;osp jj+rvkli+ ny8u/fx, .o(um 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 eu9dl /m n7j0 ofih,a*at 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound l9h0f *a /oi 7,eudnljmevel 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 registered 130 dB when aol*.m*bm6vlnl+d9 c h 0/ve yplaced 2.8 m in front of a loudspeaker on the stageheody+0v b*6l vnm.a ll*9/m c.
(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 so39*b9 shhluge und level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels diffbel g9uh *39sher by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is triple y7 8/q(jrhy bqj*0myyd, (a) by what factor will the intensity incr 0rjqh* y(/ymj87qyby ease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes,;*0d.e p vf i/0ek7ogjgr7ie4y. qhae but one has twice the frequency of the other. What is the ry7 i*v0e p.ia4ek;dfehg oq ej7g. 0r/atio of their intensities?   

  What would be the sound level (in dB)6k0ri* hg 1x,+suvmtp of a sound wave in air that corresponds to a displacement amplitude s*+gxv6trk p0im1u, hof vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a wnvplj0.u )ya.a f,v* 100-Hz tone that has a 50-dB sound level? (See Fig. 0wa*f)a vy.,vnplu .j12–6.)    dB

What are the lowest and highenwan xrmfn-o ,2-o 7d3st frequencies that an ear can detect when the sounom-f-nxwdn ,a7 2nro3d level is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge . m - +3jpj72knn/wm9a pmqhonrange of sound levels. What is the ratio of highest to lowest intensity atn3mw an7nj m+q2po9h- mj/k. p
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a viol 4kq296p m1x3hyy hxdyin has a fundamental frequency of 440 Hz. The length of the dq3 my 49k6pyh1hy xx2vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and fiezvm2 1o6*;3kv fs y,0zfza okrst three audible overtones if thasf3 zv ;1ek ofo 2y6kmvz*0,ze 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 blowing across the tvsni;:jkim1 u6 cz)(yop of an empty soda bottle that is 18 cm deep, if you assumed it was jc1;i(v:m s uk6zn)yi 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 wit mz;v;dpl. rt..ksca*:nu 1ys h open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range zaldtr;scp k. y.1vnm.; :s u*of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequ7jv(obrhcx7ml7w 52iency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its original leoj(ric25 bm7xlvw 7h7ngth?   Hz

  An unfingered guitar string is 0.73 m long and is tux4lwq ;*2 xgq c (vljsrti,t(/ned to play E above middle C (3w,/i2xq xg(rv4*tl(tq j c;sl30 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 avp me9m )(hug*n open organ pipe that emits middle C (262 Hz) when the temperature is 2pue) mm9 (hg*v1 $^{\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 vy8)4zx jm(cr$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flutedwd pi ,vrh bs 5z+ol4.7s/+jxxize86 in Example 12–10 should the hole be thatlxzs+b/w i+7i6d hsx,evr .op4z8d5 j must be uncovered to play D above 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 resonate at 264 Hz, 440 Hk z)m8hg7r 1uldgdx1 5pm)+de z, and 616 Hz, but not at any other frequencies in betwl)71pdmzmdg58uk )d1h g+erxeen. (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 open at both ends. It resonatesz9q.h(z(, k)jzrmt5 5mct muw at two successive harmonics ( ,)5r.tjz mhw59kquz (tz mcmof frequencies 275 Hz and 330 Hz. What is
(a) the fundamental frequency,    Hz
(b) the speed of sound in the gas in the tube?$\approx$    $ \times10^{2 }$ m/s

  A pipe in air at 20 b+* 4d8edq h+e.jintbade e/ :$^{\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-fjmgc) 4z/j 9myf9*(y8b wrqg long organ pipfj99j4 zm8m*) g/fc qygrb(y we 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 open to the outside a sz-wzaxm(/-fg3c ,j jnd is c (-, saz3mjwxc gj-f/zlosed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of your answer to the 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 tok. kvts e40bm1)zvgqh 05uw/u adjust two strings, one of which is sounding v 1 4b0km0)wsezu/5g khqtu.v 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hl z p/yh+xo s2rbm-qh5z:x)p3z) 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 an 0 +vxzyq;yc3v d:boo4other (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequeno zcvy+;qboyx d3:v40 cy 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 35 8n7q4lnnwt-n 0-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning4 t-wn7nnl8 nq.    Hz

  Two violin strings are rl :b)ueq;d /j8y v2czd/( yactuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two stri2cdq)v (/clyyj 8;rb auz/e :dngs are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be hearhcj-4 e5rpoy9u 1 - alb p;5e.pkbgea6d if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C p cbg oh5e.yab6ue5-p -ap4l1;ker9j and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. 5s6 7pz1lu g8wsv v7w4rrjy5s Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are soun1g s578 lsv yz67ww5s4ju vrprded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apz*me5ltt) 4nh06 k dywart. A person stands 3.00 m from one speaker and 3.50 m from the ot telz0 kt)m46yd *5nwhher.
(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 13n ;o4j52am )i) bweppe2 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 13nm e)w4;)5pei jp 2boa2 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 aum)csc8 y* d;i jny*ml19+fsnir. How many beats per second will be heard? (Assume s+*yu mmjin d)9lc;n*1 fsc y8T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a c)tb 7.ewe4rht1pzyd 51so9 jgertain fire engine’s siren is 1550 Hz when at rest. What frequency do you d4 .1orp7zswtt)gyb5 9j1dee hetect if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still88girmig4 te-yqk s9 l)i1ms 5. What frequency do you detect if a fire engine whose siren emits at 1550 Hz moves aker milsmq itg)88-sg 94y1i5t a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in 5eiq0nqo*k i-plx hv88 hx7g)frequency if a 2000-Hz source is moving toward you at 15 m/s voh85pqgl0 x-hin *7 8qve)ikxersus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they close? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equippdm9l bat-7e/m y- :y3evbnh9sed with the same single frequency horn. When one is at rest and the other is moving tow a3bymhsn /:e e 9mbldvyt97--ard 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 o -p60uqd2ft0mj h4txhut ultrasonic sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 002-u6 h tjpq4t mxfdh25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speenwun e znc :,ppdx sn:20z,8m7d of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear inze pnnn pwd2mz:0:7 ,sx8 c,un the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played ,1qn j(. o-m8d q1dr-tbav:kj-fzocs on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a sf 8d.dsjoa,c 1zk -t(- bmv:o rnq-jq1peed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeds.y xf fqh47warr 8y n:r/e .rq4t6xj+5w 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 blo8r r.yqrrw57exa+f w/44: xtn6qfy j hod is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of frequency ) hiprp s2(br8$2.25 \times10^{ 6}$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. Whep9427jhynp y n8ejobbbz(,5 pn the wind velocity is 12 m/s from the north, what frequeby5(,n8 4pezyh 27 obbppnj j9ncy will observers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if its speed at 20l y *:qo:3wg d/ihg(9lv0xben $^{\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 sound is2u da46 6c7nlvyza p)gf1qss3 310 m/s (a) What is the angle the shock wave makes with the dnqaz 3p d1s7)66y2ua f4clvs girection 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 where the speed t,g . pfz0gw3j,uz :meof sound is only about 35 mg.:gmj,0u e , zzt3fwp/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. Determ z dp7len0p*sjll+;im j/ md.+ine the shock wave angle it produc 0+i.zl*sjmpl+p m neld7;/ djes
(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 bxr ;p9;yfe jtr wy-gw0ez796 $/theta$ 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 exv *6iac:/,gw4 hlyqody;sr,cactly 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 hr6 y l,/das c:gcw;o*y ,q4iva 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 thacx.j0-b-+wayik focb q; 2is- t sends 20,000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 200 m, what is the minimum time2.j+ -a-bwc0 o i;xcqikbs-fy between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible fcg9,biq z3i1q8 1* 93;nopltrcqgharange? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pip( -4dcc (uwb bx.-/x pr/* tx:wasisz4ytulu6 e symphony. It consists of many plastic pipes of various lengths, which are opec:z yu xlxst4a /bsxc. t-u-( pri4 u6wbw/d*(n on both ends.
(a) If the pipes have lengths of 3.0 m, 2.5 m, 2.0 m, 1.5 m and 1.0 m, what frequencies will be heard by a visitor’s ear placed near the ends of the pipes?
$f_{3.0}$ =    Hz
$f_{2.5}$ =    Hz
$f_{2.0}$ =    Hz
$f_{1.5}$ $\approx$    Hz (Round to the nearest integer)
$f_{1.0}$ $\approx$    Hz (Round to the nearest integer)
(b) Why does this display work better on a noisy day than on a quiet day?

  A single mosquito 5.0 m from a person makes a sound close to the threshold ve n-hx6j/e. +-syzw jf2g+4tx dnc(aof human hearing (0 dB). What will be the sound levej+ ved/-nez2 g(fnsxxwha+4cjy- .6tl of 1000 such mosquitoes?    dB

  What is the resultant sound level when an 82-dB sound and an 87-8ll:vbrrer dbktu))c;loa c 9y r.6 1hzyz),,dB sound are heard simultaneously),b,) 8y tv :6)krcd.lr lzhoracu1 ; blryz9e?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 ak;b; -ltjf; ,v u;shqdB. What is the acoustic power output (W) of the speaker, assuming it radiates equally in all directions? u-qtj ;v;,akbf;;lhs    W

  A stereo amplifier is rated at 150 W outputc gjht6u;tw)ld xq1;( at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power output in wattsu 1 6;ctqx)h; gjld(wt at 15 kHz?    dB

  Workers around jet aircraft typically wear protective deviceu 5rs:9qj8hfps over their ears. Assume that the sound level of a psfj5uq:9r8 hjet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communicatior u+n)d ukq4jpjb6, 5ins systems, the gain, $\beta$ in decibels is defined as
$\beta$ = 10log($\frac{P_{out}}{P_{in}}$)
where $P_{in}$ is the power input to the system and $P_{out}$ is the power output. A particular stereo amplifier puts out 100 W of power for an input of 1 mW. What is its gain in dB?   dB

  Each string on a violin is tu-epv h8k) nzcz*b :yue;ux j*1ned 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 is 32 a i2 fe0y 24lb4g(xu1zhwmz0ecm long between fixed points with a fundamental frequency of 440 Hz and y04bxm(i fe h4g a1uw0lzze2 2a 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 above a vertical open tube filled with ti.kj8;mdge/9 6bm j swater (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 th8mi;/kgsjem. 6b jd t9e 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 c/i06 ma39:f knxdgyng 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)fy:3n mx0igd /c kna96 with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one ful /j9xj-e.7gxram/j rgl loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz rangess1r -eboet pg1 7z5i. coming from two sources. 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 poinz gei1b5r -s os7t1.pet 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 stati,ntz 2w1zj p*conary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is theznwj1*,zc t2p speed of the moving train?   m/s

  The frequency of a steam train whistle asf(z.xt/7 gytp it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train moving (assume cotf/.( p7z gtyxnstant velocity)?    m/s

  At a race track, you can estimate the speed of cars just by lib6n2 s-zgnuf 9stening to the difference in pitch of the engine noise between approaching an6nb-2z9 fgsund 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:r wy z-;n d5eh v9f8.evpna0h- gac6z beat frequency of 11 Hz. The shorter one iv-wvc: f 6nzy a05gepa;-r nhz. d98hes 2.40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of a railroad car as it moves wkhv./; 6gpd g87yu kqpast 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 obser k8/ph ;g.6q7ywg kudvver when (a) he listens from the position A, in front of the car, (b) he is between the speakers, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood flow in the aorta y8:2- ugpiu4:)u- zwgqf hqudis 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 tra8hf-g )u:2pq: -i4wyuqz ugudvel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 mn pytrs9zjp p ;-:gqwqr66b+3/s while the moth is flying toward the bat at speed 5 m/s The bat emits a sopy :r3-tj9rqq wpp6 +6s;bgnz und 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 of high frequency sound pulses as it approaches a moth. T(:ed8jxkef)y lvs -4 64liohphe 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 soflp8 i6y-k:e4d )lx(heo4sjv 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 from ontg25uor,hq .f:oj .rtxe14oke Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to creag5,qfjot. oux.e:1 kohrt4r2te 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 th ug;z- kj. pa6x ;thfmqz8uw* )/qbq7se presence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a living room 5.0 m long, 4.0 m wide, a7 s z6/z.a;xumq wp-t8f qjub)kg*; hqnd 2.8 m high. Calculate the fundamental frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves a long, hwwhzdw74// kslender 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 cle/z /w4dwk7whh ar, 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 human xe(hur t8xx;3 ear at a frequency of about 1000 Hux8ter3;( hxx z 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. An2gp tfo9j3wwrmf:u 4 ( observer on the ground hears the sonic boom 1.5 min after the pw uot3r(gf94j w2p:fm lane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat my16h1 eo8qcpis 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