What is the evidence thna -g2 mx3zfag16h s)sat sound travels as a wave?

What is the evidence8 -i.0 o :x wft5/b,hcrtng4k c,ggi5; fwmldh that sound is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a string to tsx/t+zshej; mst qc 2przt we:2; 3/n,he 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 wavw,+z /eetc sr;q xs/3 nt2 :2hm;tjzspe travels from one cup to the other.

When a sound wave passes from air into water, do yn,*g-e)k zlzfsg- a -lkzll5(ou expect the frequency or wavele-nzgzelkkl(-s l),-g azl5 * fngth to change?

What evidence can you give that the speed of sound in air does(y,p;olpyav s680h of not depend significano8,lv h ;y0(aps fo6yptly on frequency?

The voice of a person who has inhaled helium sounds very high-pitched. *.sz.keugl/amugy,,sqhb92 ca-t2r2z g ; bsWhy?

How will the air temperature in a r3pk+ e j ).q1(rvevofloom affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitu krguf5h a* ax9+f)1xude of sounds in vh5)x*kfg+uua 1xr f a9arious frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closeb)4bfd1r e( 4tn3xm4 vc- tqayr together as you move up ty4cba v-nme43 trq1(bf) xt4dhe fingerboard toward the bridge?

A noisy truck approaches you from behind a building. Initially you hear- a5 p*lgmp1cu0ojpf 8 it but cannot s8a1jpf5o pclu0g- pm* ee 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.]

Standing waves can be said t -w,(kqgxr)q wo be due to “interference in space,” whereas beats can be sqwwrg )k q(x,-aid to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the points s b5(mnsgxuc2b4:c1qpv c/5 x D and C (where destructive and constructive interfebgx/c5 1:q4c ssm2xb(c nu p5vrence occur) move farther apart or closer together?

Traditional methods of protecti8fc 1,h hdbzh2u9h9a0;ycnqzng 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 qf; c,z1hbu2n99d zy chh80ah 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 shown in Fig. 12–31. Each wavzvtbc c* nk9v3)q8, cpe can be thought of as a superposition of two sound waves with slightly different frequencc8ccnpq)b v9zv t*k ,3ies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer m(q-uz1 n6jtutove in the same direction, with the same velocity? Expl(6 unqt1zjt u-ain.

If a wind is blowing, will t yb8tmiw+i .4lhis alter the frequency of the sound heard by a person at rest with respect to the source? yl4i8bitm +.wIs the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in moti yj8a9ln 4i6afv r1nv6y9+zkcon 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 the highest frequency fo9418fy+kynj6n vz 6la icrav9r the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echo qpem5 n u-v5pcoo0/ wk(n5y.qof her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after sp 0 voyken5 w.u5( opqcm/n-5qhouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. Hdndt977: oic1 bfred3e.rba;5ztyv* mx)cd ; e hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocea v):3zere dnt*79b.d7 ;dcx5t modcb r;fia1yn at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavel*n,0ex0cwmv2e)hmaq r ep x63engths 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 drift-svdh+b/ :a aqlxuhdezt (6 28ing just above a school of tuna on a foggy day. Without suhq8 dzv26 -(eaxh/ badt:+lwarning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes wlakk,+ze;z8x hen striking the water below is heard 3.5 s lat l8kzx,+a k;zeer. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stonek;/pgmwt8xab8)x8 dh 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 the impact occur? Se;m88kb/ pt8hgxdx) awe Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of dis y8ynjf8grvb0(;7hmjf 3bnfsr * 9qq:tance by the “5-second rule” for estimating the distance from a lightning strike if the tempera*bfrrqv:myy q f7b;hf3ngn (8s8j0 j9ture is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a s 1kr8ta5xc z 8phxs4k)ound at 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 sop5q5lqx3w3f p und whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneouslyq+*xig fuh7vc) .dbm ; at a certain place, what will be the sound lei;cudh+ )gv b*qx7m.fvel if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally noisyulzcr69ct8cm :mxd :7 jet engines is experiencing:7xcrmctdmc8:lu9 z 6 a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas+icdx.0vfv0tvf 9bu*/ u p t bo.f5po2 for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each device?*9.tfu .ftcoi/fb 2o0xvv up 5dv0b+p 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in normal 9 ixf*:*ywqayconversation. Use Table 12–2. Assy: yx**9qiwfaume the sound spreads 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 strikes an eardrum whose area cbqmw4 si d/l9uzx3*/osx-a)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 thrism *cjrhj-eqx(,x2 7i3 hq2e more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect sm7 qcx(rjixhjq ,r23ie*h2-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 mc*:6a izyl) lyeter registered 130 dB when placed 2.8 m in front of a loudsp*cya:ll6 )yzieaker on the stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can typically detect a difference in sound level k8w s;l3sqy 0fof 2.0 dB. What is the ratio of the amplitudes of two s 8fq30sl; ywksounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sounds 8ehh:hv9 k, drpmotk7-jg): wave is tripled, (a) by what factor will the intensity increase? Increasm8hhs7dpo -g),e tkk j:hvr:9e by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacemkih d2ft e1iok)i06d5ent amplitudes, but one has twice the frequency of the oth5itoik)1fh 62 d kd0eier. What is the ratio of their intensities?   

  What would be the sound level (in -cigb)a.ej*fwc .f9 zdB) of a sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz? ). 9 ef-az *wccgbji.f   dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hx/)dk;hi0.+r 0oqjb/cgt s6 pb xmcq a 6ae(b+z tone that has a 50-dB sound level? (See Fig. 12–66.+ah+x)cgc e0/( jkbt 0r a;bm sxqqidpo6b/.)    dB

What are the lowest andd g2koi i;mhbs*5 q,4pao(y3fve8 dyxy k ;2m2 highest frequencies that an ear can detect when the sound voexb 3y 2,iof k;p4h(d;d5k8a*mgmsyiy 22qlevel is 30 dB? (See Fig. 12–6.)

  Your auditory system ca 3hk47grd7eo wn accommodate a huge range of sound levels. What is the ratio of highest to lowestre43h g7w do7k 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 funddxk ncwj,m:,e,;;hsr amental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension mwehd;,,,sj ;x :mcnr kust the string be placed?    N

  An organ pipe is 112 cm long. What ared8 n9;6ynfhx3fd 6ij p the fundamental and first three audible overt 8dfhi;p6jxn 3n6f9y dones 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 frequency would you expect from bl/ klu l)f+t*6qz+ mdrtowing across the top of an empty soda bottle thazt+l *mukl q )6rfd/+tt 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 oowfic c, rd*j7btkv1lc+ )+:the range of human c)*lwr7jbi+1oc,vcok:f d+ t hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has azz2e em qd9g84 frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it 9 em28deg 4zzqis 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 plxdeq/pa chvqf-;dv 6 a,4o +q+ay E above middle C (330 Hz).afx6 /qv+d+odph4 ec -v;q q,a
(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 organvn 2o2m4h :broq6v/ gzj5ht)m pipe that emits middle C (262 Hz) when the temperature is 2gmo oj2/vr b:)5qhh2v4tm6z n 1 $^{\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 2oq3mak* ogs;zeakd1iisyg. - p2,) dat 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 shout2ip0*ut tey fcp4m.hu 6nq.,ld the hole be that must be uncovered to play D above midd.tpu0tf*cim yte,qh4 6 p2n .ule 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 ab9l9y.1lk7 6 i2gw2rkmcymo1j o b.ae t any other frequencies r6y y29ibkj21..lmc 9a k 1lgm oowb7ein 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 open at both ends. It resonates c +k 4w,q z30iwnewy;+o m: ba:x)wgjvat two successive harmo:oa3kvgc+ww; m:z w njbe4y)+x0 w,qinics of 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 +qx (r(n(wrof$^{\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 g2 7wx8:0orlg qthk70wnj 5ub present within the audible range for a 2.14-m-long organ pixjww7r0:ng tu2k5bh0q7 ol 8gpe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2;vh g+pl7jcmcfo;y43 .5 cm long. It is open 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 the information in the g lj3;m+;gyocv cfph74raph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when tryingwhnk- uc-v5kfy4 hx )46xse0 - egqb:m to adjust two strings, one of which is nxmq )g-yxke-hh5scb v0wek64 f4u:- sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if midp*dh 7dfb0zj-+5 yn dfh3d/x edle C (262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle opkc(kq:he0 +cjvmzl7,fs * ;h werates at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle 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 brmkkzc,sjv+ *:07e; ( hfwcq lhand X.    kHz

  A guitar string prodz:zj v(e)0gl7 fv9bcmuces 4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational freq7j)g:ez9bfvz0 lvc m (uency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the sames.858;jgqglze ibdv/ vpv 8)k frequency, 294 Hz. The tension in one string is then decreasi8p bg88 k; gvzlvqsj5e)d/ v.ed 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 to play mk4 o yue-gtip6 .j:c7ziddle C (262 74jt6.ukzcop :-egi yHz), but one is at 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 fre-cbehr0 pz,z ,quency 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? W0 ezc,,-brzh phat 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 stands 3.00 m from one speaker and rx;1rsep 8(wzmtg.g) 3.50 m from the og 8gwsr ex)p1zrm.t;( ther.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating at 132 Hz, but a piano 4- h cmhfsxi5mkzpy;-beh); ;tuner hears three beats every 2.0 s whep )y;zh -f;ix45hb-mhcksm;en 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 masi2 p0;li5 r-p+: lejnpzpho5ny beats per sl;isp5e0-n:h p l5 jp ipzr+2oecond will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz wheng4; x:bo0jyrc at rest. What frequency do you detect if you move with:y b4gr;c0jxo a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do yo e r*7ux+,jcmsu detect if a fire engine whose siren emije+, ur*7cmxs ts at 1550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift ivo*j fzk0ykne;97 (m uc s10ajwe66hun frequency if a 2000-Hz source is moving toward you at 15 m/s versusaw c 9o76j (zvenj0y0;*umsk ufhke 16 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 equipped with the same single frequency horn.k/djb0-tbf k4:ma*nhfgm; k8 When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the hor8g:-* kfb;n 0akmt hmjf/k db4ns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultr )xws ;t pyyw+fvue1.2asonic sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the rew 2t1s+.wyey);xpv f uceived sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat wb2 f3unzms+4emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency d4wf sn z2mb3u+oes the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played ahdhz9dynp:s z8ud gq 9 b9v1/i;0iz)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 speed ;9:9 z dy8biz9h/d0)dhaugvs 1qipnzof 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to t,jgf) t(dmu30ui+ nnprv .r p-rk- ,cmeasure 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 dire+iguctpk) u0rd ,3n,vnr m-.trf(jp -ctly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of f6e7h u7h823pl-d kfjm+brl hfrequency $2.25 \times10^{ 6}$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 sodw2(h1ud /gl/ srklv)und of frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are located, at reluv d lhgw)r(/2k/ 1dsst,
(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 20munce jnt 946h 68 j)ot1/tplw $^{\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 speedj xivvf6638 ow of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of thw iojvfx86 63ve 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 ofna .( ihz ;7g lj ypeeobv5k73()ncd2r sound is oj )azn b3rdgkio.nhp;72e5l y7v( (ce nly about 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $

  A meteorite traveling 8500 m/s strikes the ocean. D2( gbk5l ypf2 bgm*l/ 3 d.q0/v+jgvh:vfdprq etermine the shock wave angle it producgbql2fg0dvgpk rqv 3jmfdv+*l/ 2./:ybh 5(pes
(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 i-iugy+wi1m c, aq8c-srw9s * $/theta$ 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 a tu4hwfbxk5f y63 5wn5 *ubn-ebove the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plhnk be u5f*6w3x 4w5b5 fnu-ytane 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 6it +yvfdycuvp 804e*h pka. ,vg.0 swdevice that sends 20,000-Hz sound pulses downward from6 ,pw0 8* .cytp+vvhs. ei4ufva ygdk0 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 time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible 5xw 9rt/h1*9enj8daqzkpj; cc (0m exrange? $\approx$    octaves (Round to the nearest integer)

  A science museum has 3hte0*u tlq26e xa(fufv.q.f a display called a sewer pipe symphony. It consists of many plastic pipes of various lengths, which are open on both .*fftfe0 (. aquulq 6h3evxt2ends.
(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 tv(pt875p nl zghe threshold of human hearing (0 dB). What will be the sound vlpt8(7z5g nplevel of 1000 such mosquitoes?    dB

  What is the resultant sound0 iogomxp3k 1d2+uk6qkbj:6x level when an 82-dB sound and an 87-dB sound are heard six130poiq2uxm:k6 d g bk6ojk +multaneously?    dB

  The sound level 12.0 m from l7q9a fx1 0voullb5g/ a loudspeaker, placed in the open, is 105 dB. What is the acoustic power output (W) of the speaker, as faqub1 xolllv79g05 /suming it radiates equally in all directions?    W

  A stereo amplifier is rated at 150 W +/ w8kuqo0avbm m23 6sru-;u x 9oktxjoutput at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power ou8km9ut;o/m v u wx03+j x2qaokb-r u6stput in watts at 15 kHz?    dB

  Workers around jet aircraft typiczdn,eyi 7v6w vfm2 s:(ally wear protective devices over their ears. Assume that the sound level of a jet airplane engin2 7em 6:d(vy vnwzsi,fe, 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, thnnqm/)l7yta/ e 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 arkhjjv8;ytvq b, 32 :r 5hg)ya frequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ =    $\mu_{A}$
$f_{B}$ =    $\mu_{A}$
$f_{C}$ =    $\mu_{A}$

  The A string of a violin is 32 cm long between fixed points with a funda9g4v8.nq)z2diwg dud*t30p w qht7 a nmental frequency of 440 H24a)twih3tg v*nwpdn7dq.z9 d g8q 0 uz and a 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 w3q 02e6 kq1gvipm( kxqr+vm) mith water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water lev km0q 2q k)6(ipv rvq+xe1mg3mel 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 one e gp 5mhk o0,rk(r8);i0derrh end and also 75 cm long. How much tension should be rgm kr0h;5,do ieke8)r(0rh pin 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 obs(+,tc us rel,v9*wssuerved 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 in them 4,21ri3i8hi1 aj(6qc(gmzucit :fyca6 yv f 500–1000-Hz range 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 abo((18m4v hi1 cyarit: u2j,afg 6ciyi c3zfmq6 ut and finds that the sound level is minimal at a point 0.34 m farther from one source than the other. What is the frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The conducto -eld(g*0f z xajo0jxi1en .ygd9d:h(r on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of the movxa(gg1dd0e 9f0( jd ozlyh*:ji-xe.ning train?   m/s

  The frequency of a steam train whistle a (qmnryrkil5ii4qvg8e15(:4t0wl4 f hk m8fe s it approaches you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. How fast was the train movinl 48 hiwn5yr5(f0 mqiqkg4eek:lf v4m8(tr i 1g (assume constant velocity)?    m/s

  At a race track, you can lh 2nc/oynm ku 7;)r-testimate the speed of cars just by listening to the difference in pitch of the engine noise between approaching and receding cars. Suppose the sound of a certain car drops by a full octave (frequency halved) as it goes by on the straightaway. How f;rm nh)nuo2yl-ck 7t/ast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11 Hz. 8 2z*8 yznofzv qu0jp)ss:fi/The shorter one is 2.40 m long. How long is the o)0z *zn2 fsjus8/yzq8v pif: other?    m

Two loudspeakers are at uxu 5og.hq;m 0opposite ends of a railroad car as it moves 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 5ou0xmqh; u.g 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 7,wj 6 mdhp);de a3emnflow in the aorta is normally about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves werehejd7 )3pn6wm;,d a me directed along the flow and reflected from the red blood cells? Assume that the waves travel with a speed of $1.54 \times10^{3 }$ m/s   $ \times10^{3 }$Hz

  A bat flies toward a moth at speed 6.5 m/s while the moth is flytsgy2h ,g5o5 nc4g;/1gmlp h, w-tdc ling toward the bat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequencythgolgw/ nmg5cglhtc-s 5y, ,;d142 p of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series of hig(/spsz;i;wfawv a(7 xh frequency sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detected by the bat so xwa7z v((pf;/isw;as 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 one Aw5c.imxj:fjtd.6 a *so5 un74ykof2q. +z zzj lpine village to another. Since lower frequency sounds are less susceptible to intensity loss,fz7.my zi5o j .a5j: 2s4tjkoqzudwx.c*fn6 + long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundamental frequency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be compromised by the prese+v 91n.kwkbwv u(thz 1nce 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, and 2.8 m high. Calcul1u1. 9wwvtkkv+ h (bnzate 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, slender aluy; dthk f5ag;y.fev:gfk t:zro0i55 (minum 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 “seyg0tk v :z55;5f dfy(hofa:i ;kt rg.ing,” 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 human ear atm kj( fo1074uqv6hqfs a frequency of about 10qoju4 6fh (1kf7svmq000 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 7)ab a7*axe:givo+u oobserver on the ground hears the sonic boom 1.5 min after the plane passes directly overhead. vg+ou) i 7:a7xa*oa ebWhat is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedbx uexcx c9)y3um )(zyq4,cxd/ oat 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