What is the evidence that sounlo7 91toqz8 fgqr5k/id travels as a wave?

What is the evidence that sound is0d mzney0- 3y1;xvpb n a form of energy?

Children sometimes play with a homemade “telep;cx, uu /td1ffhone” by attaching a string to the 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–f xduc;1f/ tu,29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do yf ar1pix uxyyr7 j*tqj4j**2(ou expect the frequency or wavelength to chanr (xj* x *fr 7yp4tja*qij2y1uge?

What evidence can you give that the speed of sound in air does nco ; x1:rxvxs5h;q kk- zsq5zil6n,q0ot depend significant5: k oc5,xrx;-z1kxinqq 0vzq l6s;shly on frequency?

The voice of a person who has inhaled helium sounds veb)zvd64d e:k c ywv+a2ry high-pitched. Why?

How will the air temperad8 v-y)kn sldr5 2id(xture in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce thexk; am u9x-dy.t ;aa9sf7 k/bb amplitude of sounds in various frequency rangfaxa9 /7.-ybukd b k;ta9 x;smes. (An example is a car muffler.)

Why are the frets on a guibgbx +h4)8qyctar (Fig. 12–30) spaced closer together as you move up the finger +)bcxygh4 8qbboard toward the bridge?

A noisy truck approafkd,xe p,5mp hn7lqx-(p.e8dches you from behind 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 diffraction.p p de(l- x5f.kp,mdx8e7hn q,]

Standing waves can be said to be due to “interference in spa tw83 pt optn,3a;cxg+ce,” whereas beats can be said to be duexct3a+nw;p3g,p o tt8 to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the psb9+7dqf z. cp23r9mn. pp qpzoints D and C (where de2.3p9 pzdr .7+qcmnzsfpqp9 bstructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecqfc;:q0( gh 1g)lo ;gf2l-*o5q0murvx g ok qmting the 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 device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient rf:vx 5kg) u;oqommqlgo ghl *g00cqq1;2-f (noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can bez+ ,kaf:gs o tpjo/o:4 thought of as a superposition of two sound waves with slightly differe +tfojo:pk:g so,/a 4znt frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shif5xh1b:)*jdznkpxpqd -i,9pr +kyh y 8 t if the source and observer move in the same direction, with xz: )dpb59rkj y*n+i1dyp 8 kxqh -h,pthe same velocity? Explain.

If a wind is blowing, will this alter the frequa x,c2:jhi gi1g wi*(kency of the sound heard by a person at rest wixhc ,ia12kj(: *gwiigth respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in mom*rel;7i( h- vz yp*)zt7 ftkttion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear th rfkt(* yv) lpht7*emz;-it 7ze highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by likq8o7 i 3lce6ke+lsi.stening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s afi73. esco+klle86 qik ter shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He 4g.8dls/tg mp m 4q seno9q4k.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 1560 m/s (Table 12–1) and does not vary significantly w9q8tg/gk e .4 d44 pmsnmqosl.ith depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelenr wuww oth9 52a8lz*5vgths 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) i7j9.*ure) aun6*dquf dg sf of tuna on a foggy day. Without warning, an engine )g)* q ur*ufisane9 u.6j7dfd 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 splash it makes wq hbwd4 oxpth g1:6-z0hen striking the water below is heard 3.5 s later. How high is the cliffq4z ho tdp 10bx6gh-w:?    m

  A person, with his ear to the ground, sees a huge stone strike thp eyj1co .a(v o((1w.uvxn6pde 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 the impact occur? See Tye16o d(. .xwcuo1npp vv((a jable 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one m 2a8ocsqum0 -k; uyzs5kh )b+cile of distance by the “5-second rule” for estimating the distance from a lightning strike if the tempeyuc; kka+-)mqos5 zuch2 b80srature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the paig6y /mi9dex;wn level of 120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of a sound whs.-bh) ;kam ys agn)g0ti9w2dose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simult lsy-)fc5po 9ch xe;h6aneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, 9ly5cp hcoefsxh;)- 6not dB’s.]    dB

  A person standing a certain distance from an airplane with four ena -iyv2 msd54qually 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 ony mands4-iv5 2e engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a siurdjq h -48k;vd*c ,nggnal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of inten;*vdk,r8 udc qg n4-jhsities 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 igbdt9 j0 n4ef(n normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on t dt9(bng04jf ehe 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 strik;omm7 3exb +cslp 0)hyes 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 2a vud6n +u8euvf 2nz yuvx)u7;ypl0 :550 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turnxlvn7 zuvuye :fa;0y5v8 p)2d6u+ unu 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 metereg8; 3si/ecvd jfx-b+ :b+ efa registered 130 dB when placed 2.8 m in front of a loudspeaker on the ecbx; fs-+ ef g:a8evb+id3/ jstage.
(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 sj)p3d a ry6-i(/e6dh +mibj +ueko8+vxv*xva ound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by thuy a6 vdpv+3e)( ekj- v 6/+8*hd +jxmbxoraiiis amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound w -bkn.cmot0 a5ave is tripled, (a) by what factor will the intensity increase? Increase by a factor of 5-k0 bmt.cnoa   (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but on.k9*npv7hjc e,;9l ceh.vt qs e has twice the frequency of the other. What is the qn9lkc9 tsv vj ,7c*.;e.hhep ratio of their intensities?   

  What would be the sound level (in -h8dqjwn. j+jj0d2yxn2qq-j dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of0j q jqnj-qyjn j.d+hwx22-d8 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what +wkzx ,4xe rypxix +/tu+s*kr7qq v2/ sound level to seem as loud as a 100-Hz tone that has a 50-dB rtsewxqx+u,rk7/pz2 vi 4 +x+y/ x k*qsound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequgxso-r-.s+s+ nqzot5 encies that an ear can detect when the sound level is 30 dB? (See Fig.+ xor+ ngq5.-zt-os ss 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is.w -vr13rxvvyt/i n uiapkvyg,26 (a9 the ratio of highest to yx,v/r(p69 3wa y nr.gi2vk1ta ivvu-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 Hz5 clbse1b*kq,2 se 5dn. The length of the vibrating portion is 32 necs e1*bql2 5 bsk,d5cm, 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 first threepdbc rt*x 5z5tx*e:b 8 audible overtones if th rx tx*tb85b5:cpdez*e 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 txndr9ya bav1 d/x5x ;smwe 7z(x 046vexpect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tubasxxz9vnd5adx/ t b1 vw;xe4ym7 6r (0e?    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 spd kzh7 rv(8q u;nc7jf1anning the range of human hearing (20 Hz to 20 kHz), what would be the rangev1u;zfcdrhj78q7 (k n of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string hayg s+jkyik5rwzd4*. , bq3o:ls a frequency of 540 Hz as its third harmonic. What will be its fundamentkoykdj g q,r+5.3iw*zl :b y4sal frequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E abovquw; p;1icl* 1qhq:nsxchxuu 2 3)gv- e middle C (330 Hz) uun*):2cqw ;gqpqv-ihs ;hu3xx1 l c1.
(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 Hz v1bfzr*w0d tnoa(7zf +vjk/2) when tf* 0/7vnv bj2wt 1(zofa zrdk+he temperature is 21 $^{\circ} $ C.    m
(b) What are the wavelength and frequency of the fundamental standing wave in the tube?    Hz    m
(c) What are $\lambda$ and $f$in the traveling sound wave produced in the outside air?    Hz    m

  An organ is in tune at 2ink,a45aton)npa xp7 45w2 oz 0 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute ingy :4.z55g .hr 5jug;vtl(ax0ugrtuqcam3u. Example 12–10 should the hole be that must be 5uamzvuc;g03jg:hqag u 5 (.u .y45gr.xr tltuncovered 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 Hz, and 616 Hz, but not at a3tm;sgkkt 4x *ny otgt3x4mkts ;*k her frequencies 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 9 o vw:ya10xib1.80 m long is open at both ends. It resonates at two successive harmonics of frequeoywbiv1 xa :90ncies 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 d tdzof5( o nz 5;mvpgd)gy8gb424h7s$^{\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-)r y( *adz+z/m; kcnrmm-long organ pipe at 20/zz);*cr(knray mdm+ $^{\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 ab8f6(rh5kn + m hmok0ind is closed at the other end by trm+08k h mfkbonh6(i5 he 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 to ad3c xvfe5,k ny-just two strings, one of which is sounding 440cfx n 5vke,y3- Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (26:im/o-cet 5 wz9rdg5 yo jt1-sz+5ubi2 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while anoth aj57nek 2 6gissbm*2yer (brand X) operates at an unknown frequency. If neither 2ym es a75skin6gj*2 bwhistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded witb ;7y(p/lkz qdu(h5ag5j ; ymgh a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. j;uk7bmq/a5 (gdy;p(h5 lzgyWhat is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension in onej0rk-ypjl6 )ydh s* f/ string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are plah/ryjfypl*s d6j-) 0kyed together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two )4g wyju*qp +qidentical flutes each try to play middle C (262 Hz), but one is at4y wq+*q pjgu) 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a 1fpxhk*7qgm1d-na 3 ufrequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is hearduk f13nhpqg7 * x1am-d. 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 person stan (f1i9fs9-x zim7hl r6jzp3 ilds 3.00 m from one speaker and 3.50 m from the otherz(im7i rf69jhl-l1pxz39i f s.
(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 vibratifq 8 oi i35 dth:+yb2:kiugd3gng at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 1tdg h28k+:d3yi iofiqu3 b5g :32 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 6hi *erhzp9twz 9..qrm in air. How many beats per second will be heard? (Assume T = 20 9iw.rht p6ehr q.9zz*$^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certaiy*a 2/8zr*m 7uq wajn9y/ydjun fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30 m/7ju ndjq 8yaza//myyr*2w*9 us
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What fsvi4h* 2bz4tjpf d7j8 requency do you detect if a fire engine whose siren emits at 1550 Hz moves at a 4 b hfz4 vj8p7t*ijs2dspeed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving toward you at 1 hu :9jvq7k(2r3elqwoj6a 0 lqq (o746amqbiy5 m/s versus you moving toward it at 15 m/s Are theq (7jmb0qyarqa lq7vo6k 9l3oewh6u4ji :(2q two frequencies exactly the same? Are they close? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with the same single frequency horn. When one is at,r,88ki i13covgc+qnild ar3jtg*3t r 1gc3r3jt8 giqa*kiid, ctl,83nor+vest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz;x. vga3goq1 5c/uvma and receives them returned from an object moving directly away from i 3g; v5avqgox1c/mau. t 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 j., xwl fa2j*/oj djn0emits an ultrasonic sound wave, l0 dj*.wjxaj/2f jon with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Dopv 94 l6-ipmuyopler experiments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played thv -lpi4uym96o e same tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound wavwvov0k zuoj ko )942q0es 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 arteries at 2 cm/s directly awaowj )v4uo vk9zoqk20 0y from the sound source?   Hz

  The Doppler effect u0n o5ofc-uj u2h1;koz sing ultrasonic waves of frequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of freqlz; x. /j8*dww podn)puency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who arew.w *; /pz8)lddxponj 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. jype2kmk h) 5huviirv*6o.; 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 . 0tpm5gxcnh sp( ;z*p2.3 where the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of the airpltgxp phz5 (cm0nps.;*ane’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 etv9p.+r(qy+rpze2 ,qjmz s *uj a2;cthin atmosphere of a planet where the speed of sound is only about zte ;qejv +,mq(szr+cr229payu. p*j35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s strikes the ocean. Determine theh9s-ag)kdi 9w i doiryf 7:ea35)dm1o6/ oiav shock wave angle it produceshdg9o9 6o:i efky)) ovm iawda-i/r3i15ad 7s
(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 wwt3vd(v+m6.twew ki4 pt.s -o z 50ac$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead a :tqzvdw(u+jz6 8 sx(snd see 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:szsw dtj+zx(u8 (qv6 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 imbbn h. e gacuk4.qy9f5- )7cthat 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 tgfi.bmbe ayc-nu79 k.4 q5 )hco work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human aulfbn02(vdx dld )7- yedible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pia 4+q8yw-y y gk/+nmrppe symphony. It consists of many plastic pipes of vam+a wnkrqp y+4-8 yyg/rious lengths, which are open on both ends.
(a) If the pipes have lengths of 3.0 m, 2.5 m, 2.0 m, 1.5 m and 1.0 m, what frequencies will be heard by a visitor’s ear placed near the ends of the pipes?
$f_{3.0}$ =    Hz
$f_{2.5}$ =    Hz
$f_{2.0}$ =    Hz
$f_{1.5}$ $\approx$    Hz (Round to the nearest integer)
$f_{1.0}$ $\approx$    Hz (Round to the nearest integer)
(b) Why does this display work better on a noisy day than on a quiet day?

  A single mosquito 5.0 m from a person makes a sound close *v5nv /bg4kne f,hq2dto the threshold of human hearing (0 dB). What will2k/ vvn, qgeh 4f5b*dn be the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound ll/od qf93bq1bevel when an 82-dB sound and an 87-dB sound are heard simultaneouslf39/qobd b1qly?    dB

  The sound level 12.0 m from a loudspd- , sr ;/fh:hawrg jc4 m4usclp;e.f(eaker, placed in the open, is 105 dB. What is /u;rlpd,r ;-am.:hcf e44sc jgwsh( fthe acoustic power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 15c 38h2nvyg+ 0wz zq40d .rrje) tl2hdb0 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is 02rz wnh8 gvr4ljdh qy.2ec3bzt )0d+the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devicesmk9p:vh;mz .4hxfon 4 over their ears. Assume that the sound level of a4p.9 zf4 h:nvo kxmmh; jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, the gai87 xedg 4wz)qiu 4c+c:uoc 7zgn, $\beta$ 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 frequencxzf; 8.5dkphf0,7af oxaf f0n l: eov0y 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 a(t,bk* a.ygk fc-c(u32 cm long between fixed points with a fundamental frequency of 440 Hz and a mass per unit length uccf,((k-* tag baky. 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 w0mo(meoeivqz:n a-n,5mu/9a/51lkde) c e fmater (Fig. 12–35). The water level is allowed to drop slowly. As it 5 )a-m mv,fak/emo ( 1 9n/:ce5omze0lne uidqdoes so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of ma5vzdgd +q)wj64 cz; uoss 2.10 g is near a tube that is open at one end and also 75 cm long. How much tzg5 d ou w)v;4cjd6z+qension should be in the string if it is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to reson -lc v,*g ;k6ykqpu(plate 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 500–1000-Hz range coming from two sources. Tapj-*i aa a. 5uop ougzlh-a-2f,/y8ohe sound is loudest at points equidistant from the twh8g/,a ajo2aau 5pap* -f-uoilzy- o.o 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 stat;-s:n3(zt; ccbrb2 ezyb b tg*ionary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of the moving tr gs*t 3zb;b :c (b-n2yztbrce;ain?   m/s

  The frequency of a steam train whistle 592y haoow bi 5s7 ckl,gnkwqgb*(j*/as it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How bwi/cs w kgj7yogan**55,oq9k hbl 2(fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the speed of cars jus9c11.g1n.v9 i.cc awduvqup st by listening to the difference in pitch of the engine noise between approaching and recedicqp 1 i dv9cga9v1c. wu1s.n.ung cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11 Hz. 5 j ;-p pol7ifzy)hgq4The shor plz)if;qjph 7oy4 g-5ter one is 2.40 m long. How long is the other?    m

Two loudspeakers are at opposite ends of a railroad car as it movek2;y rn5b mr+rs 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 iyk2n5;rmr b r+s between the speakers, at B, and (c) he hears the speakers after they have passed him, at C?

  If the velocity of blood fl-j k.spe;, 3uh zkrvb3r8m1yzow 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 z3.3s kpz- r1 8rjbv, y;ekumhfrom the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s while the moth is flying,hiy 3eotez3ant(8 8r toward the bat at speed 5 m/s The bat emits a so o (erhz83aye ,nit83tund 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. Tb qa*p 1lt-fc;xx*co: he 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*xct;- qo:*apcbf1lx 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 signajvo,kik3y /woy0i q( ,ls from one Alpine village to anoth,/yjki ok yov(q,3i0w er. 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 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 caad n y,brj5u, j-bg,4jgp8 7dcn be compromised by the presence of standing waves, which can cause acoustic “dead spots” at the locations of , prb 78nuj5cd4agj ,-ygbd,jthe 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 “si-tl tp+keqvw7k *t15.x.upfe5 e/mr lnging rods,” involves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or emimqr/x7ep5v.l+k*t -5. e lk1 puewtft t 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 hearin)n3 :c-b p)7sqlgxq7pf.iuk/b+ j vssg for the human ear at a frequency of aboul)x-pifguns7k jb/ qb+7sv pqc )3s.:t 1000 Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on the::go2 ezgi2mcaqr (g5x:*3+ rclahsl ground hears the sonic boom 1.5 min afteroceia : ql+:m a hr:22z(53*glsgxgcr the plane passes directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is0a-qt2ea vn j 720wcnlpnhi4ww ;3tw ( 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