What is the evidence that so( ew9vj* pkex1und travels as a wave?

What is the evidence that sound d )xy/ev ol8 +abk8wmwjrv/89 is a form of energy?

Children sometimes play with a homemade npr7+:ocm ujn*nl- 8sire/g1“telephone” 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. 12–29). Explaii -+n/lm 1nrj:cu8 *s7o eprngn clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you exp8dag o *dn5uh(ect the frequency or wavelength to chanu(*8 aoh d5ndgge?

What evidence can you give that the ai-q-q evj* 6mspeed of sound in air does not depend significantly on frequency?im- 6q aqve-*j

The voice of a person who has inhaled helium sounds very high-pitch/etn zg*2*i)4dhycm ded. Why?

How will the air temperature in a room affect the pitch of orga( -fp/e7en ukxn pipes?

Explain how a tube mightbyumitvojxwpn2/j;1gla8i- f 4k9 ; 6n 64 tfi be used as a filter to reduce the amplitude of sounds in various frequency ranges. (An example is a car muffler. 8u4kx;iitbpgt6yf /j9nln 2m6af 1oji-v ; w4)

Why are the frets on o 2yz6 f5a(wpeea9j4 ,gvrki4 a guitar (Fig. 12–30) spaced closer together as you move up thar495(fevi ,6pyo2 eaj4 zgk we fingerboard toward the bridge?

A noisy truck approaches you from behind a building. Initiallg;y32tj5kuv 2m:r ta s 9voke9y you hear it but cannot see t :2jkeu aysg92r9 v3votm;k5it. 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 to be due to “/+iz8f(k:wwo akhz a(interference in space,” whereas beats can be said to be due to “interference in time.” Exp+zok/kw fhi((8zwa :alain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the poinpdq)i rakajl l3)* 8h,ts D and C (where destructive and constructive interference occur) move farther apart or closead)jlr3 )kphl*i,8aq r together?

Traditional methods of protecting the hearing of people who work va9 irth9o2w+zqu kog*c. t4;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 i t vazrku9 go42*;cqh9o+w. itt 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 wb4 f lt3f0 1+dncetqz/ave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the/e+4 tqc13z bdlnf t0f two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in thb9 y5oo1cpp 1te same direction, with the same veloci obyp 1ct95o1pty? Explain.

If a wind is blowing, will this alter the frequency of the sougqs flt5t-+ i0b- *skvnd heard by a person at rest with respect to the source? Is the wavelength or velocity cgl5f -+ t t0sqkisb*v-hanged?

Figure 12–32 shows various positions of a child in motion on a swing. (ov-cb n xzz3r-)/elyA 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 frequencnzvl3b z -yx) (c-eor/y for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echr(qe 11cybk 1oo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of th1yckq1e rb(1oe lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his snuf/j9*z qxx: s1:kg8bk lsp/ w5s rq3hip just below the waterline. He hears the echo gzn/qf 5kw ss*br:u3s9kq:x/xj18lp 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 with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air at 20* * 3)jfgf z0cyiedc1u $^{\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 a-w 6ib oku9xo8r 1rdx(bove a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. o(-8rkbx 6 d91iw xuor12–33). 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 t*8poroc x k*q2f tbmex+: /b+aop of a cliff. The splash it makes when striking the water below is heard 3.5 s later. How+b2qmf x a**/+e8tc xr:pk obo high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the cj4lz5 kx3(raa; +scih oncrete pavement. A moment later two 5 rj (;sakiz3+4cxhalsounds 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 Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distan,h-fqk+ lg*n(k d db7rce by the “5-second rule*b7kdh( ,k glq+fd-nr ” for estimating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound atddu( b)c70u6c*jfee w 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 sound whose xqn*3u u+xv;vwv/o4z intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce hj37x:h 4xq.fl yn ac:mdp896vinon7 a sound level of 95 dB when fired simultaneously at a certain place, what will be the sound level if o ma4 oh:d7lyxx j pfnvq83:inc nh6.79nly one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain dis w3(x(+fxdcd (lauy (f90 noz(r)gnyttance from an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What +yln()ad((0 ocu zgd3 (fyr(w ntx f9xsound 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 -sfkt/; z je-ksignal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the r/; tj-zf-ks ekatio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound-b h0;jc8liee from a person speaking in normal conversation. Use Table 12– - libh8;cje0e2. Assume 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 st0 ti9) w6qx2kdtx5iz lh-2rem rikes an eardrum whose area is $5 \times10^{ -5} m^2$ (a) How much energy is absorbed by the eardrum per second?    $ \times10^{-12}$W (b) At this rate, how long would it take your eardrum to receive a total energy of 1.0 J?   $ \times10^{ 3}$yr

  Expensive amplifier A is rated at 250 W, while the more modest amh+(b3vz tctv0r1i+fr plifier 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 turn cb 3 ++h1vzivr0 rt(tfto 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 placed 2.8 m in u *18fcjifn:y8 a ltn3front of a 1ucf:i*3ntl8n f8j yaloudspeaker 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 of :m( jvi*varq62.0 dB. What is the ratio of the amplitur6 jvva*q(i m:des of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intes-el y s2j77)0fq8um 1cmy8w/zvi kmcnsicj8 wi78 y/lev0ycm ks27fq -muzs m)1ty increase? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equalr3gtqwb 0c cnv5r7ce r)a) 3x2 displacement amplitudes, but one has twice the frequency of the other. What is the ratio of th5 r e7wcvcbr3 g32qnart)cx) 0eir intensities?   

  What would be the sound level (in dB) of a sound wave in air that corrok40x b9)hjhh esponds to a displacement amplitude of vibrating air moleh)9jh 4h xob0kcules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have wha3 i lu nji kpu21e8goqt 5k4i2j:o2cl7t sound level to seem as loud as a 100-Hz tone that has lupkkioe7o8:t cg2n 524iq2l 1 ijuj3a 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and higni -zgquhs1n qt0l .57hest frequencies that an ear can detect when the sound ign t5hu7-sq1.q 0 lnzlevel is 30 dB? (See Fig. 12–6.)

  Your auditory system c7y-jx(xg 5k.++lp m kv fa-pepan accommodate a huge range of sound levels. What is the rati(palyx.mp f-e+75kx gk pj-v+ o of highest to lowest intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental frequency oftdt.*slrfva ,b ; 4/tgvb9fb5 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be placebsl *t4 ,f fgb9r5v;bv/ a.ttdd?    N

  An organ pipe is 112 cm long. What a3rf o 0ppib06f.y,wq v.x1ifure the fundamental and first three audible overtonesfupifi xy vp.0w,qbo.0316 r f 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 frequenc8(r9w,zyl wke y would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was awr(w,ze8y 9l k 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-tu*v bzs)7uy.v.ga ek t;be pipes spanning the range of human hearing (20 Hz to 20 kHz), wha;kvyt7 )*s..u g bavezt 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 a fr rl aiy ,i8z0)smt-wg,equency of 540 Hz as its third harmonic. What will be its fundamental frequency if itm i,,ag ysli0t)- z8wr is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tunedp ubrds1+a9u1 e2dau-/gnk 3x 351 p;vxtgmws to play E above middle C (330 Hzx+sute5v 1 3dmrb1gupg daxwa2 -1/ k39n;psu).
(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 opf8dtd;10/u bnq8)zhy6wy saf en organ pipe that emits middle C (262 Hz) when /tf ;1an8zy qws)8yudfb60hdthe 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 2s9ofb t 9( dxz i1u3/e( xc*:yqa+nbbi0 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute inj .dna hojh 9lb2su6 dsrn)14; Example 12–10 should the hole be that must be uncovered to play D above middle C at 294 Hhad16 r j) jlou2.9nb n;4dhssz?    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 resonatv(8d zhf.let8 e at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an ope8 l fhv8z(e.tdn or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.8c87i: cd0 d4 dks4vhmf0 m long is open at both ends. It resonates at two successive harmonics of 8miccds:vdk47f d0 h4frequencies 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 o5)jp) m/ztat$^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are present within the audible range for a 2.14-m-long orgghv c s+8x4nc)an pipe at 20 +c gx)8 hcn4sv$^{\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 outsim ajjqcvfup ;,3283mhde and is closed at the other end by the,p fha ;2cujq 8vm3m3j 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 tryisg dqdjqio5(*;p9lx 0ng to adjust two strings, one of which is soundi dqjs ipgol5;(90qxd*ng 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz)i xnzj9-jbv7*ip 1a+ e and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while another (brand X) op3mocp /bl6u6f,mwav-6 bu9yqerates at an unknown frequency. If neither whistle can be heard by humans when played sepa69v/bl,wf-b3 o6am6 c pyquumrately, 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 produce gtd(a)dd()j(i1a ciss 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 frequency of the stringiasd1(ta d()cji( gd)? Explain your reasoning.    Hz

  Two violin strings arewn z*l*7l z/gpo.lbz 5 tuned 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 strings are played together? 5ln/ o *llz* z.zwpgb7[Hint: Recall Eq. 11–13.]    Hz

  How many beats will be he)rr1idw61x -zb boul 1ard if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C b16orui zbxw1-)rd1l and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequim ,wbl4 3dz6cency of 441 Hz; when A and B are sounded together, a beat frequend,c46bzw3 l micy of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A per llfkfq-o 3m; hh9ok)/son stands 3.00 m from one speaker and 3.50kfo-9mll;/ok q3) fhh m from the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating at 132 Hz, bu4awlb13i:e.d6g- -dmrcu:o n sjmmi+t a piano tuner hears three beats every .:n iol36dmj+rw-sd1: ab g4-e iummc2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound of wavelengths 2.64 m and 2.76 m in air. How many beats peu:yc(q8felw1f yk+g 5 r second will bu5cf( y18f w+y:qekl ge heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire )rubmbrr 52m*3h4qlh uk,jj il q0):l engine’s siren is 1550 Hz when at rest. What frequ3 b q))l*4rhrmruk j052uj: hlqi,lbmency do you detect if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a fire y6uy p9 uf7hs.wymg o2ijy 3+4engine whose siren emits at 1550 Hz moves at a speed h.uf2my6 79y jp4y gwy+s3u ioof 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 towa ofxkc9e.()jwrd you at 15 m/s versus you moving toward it at 15 m/s Are.oj(ek xfw9c) 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 eqix,:cs)3tr, kds6, tdqjbr,d(qk4 ehk2e rx3 uipped with the same single frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequencyts 3xsd2r,bki e36kcrk q ,4rh :d),q(xjet,d the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receives txd 6-hjepkw o7b7o gbvo)3 *)them returned from an object moving directly awgwotxep-vbodk7 h) o * j7b)36ay from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat emioz:p/04(hura (xhkc 6y8n nyu ts an ultrasonic sound wave with frequency 30.0 kHz. What py6 n(r hzyhx4 a 08uu/c(nko:frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a o y/mzcye7e8b- ;)lzrmoving flat train car at a frequency of 75 Hz, and a second identical tub 8/zbcyrele;-)m o7yz a played the same tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeds. Suppo,y0 nd 607hfxtp:e d.yi4wxeyse the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s .py de nyi4:,7wh t60dexfy 0xWhat is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic mcjtg ax0yq 3e328iepbhz*1*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 frequency 570 Hz. When zy8ex 9ua*ff4xa ;oi1 the wind velocity is 12 m/s from the north, what frequency will observers hear w;1z f8x4eaoafyxi9 *uho 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 pbjx 4( 9 /z3asuwx+.xpvqa0)j qgvs7its speed at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where the speefb3 7bx /f28n nidw9idz4 0ozrd of sound is 310 m/s (a) What is innbdf/0zd74 89zo2w x 3rifbthe angle the shock wave makes with the direction of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmvcgc 9 z)liox7kd 3;8xtf:d/rosphere of a planet where the speed of sound is onvi )k:c ;xd dlr3czt /xgo897fly 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. Dxg1 lps pfaf79wc42d7etermine the shock wave angle it pro sg7a ld41w9cp27fxfpduces
(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 qif0e1nn 7yzp(3usy3$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a plane exactly 1.5 km above the ground flyi.aayx+/phm ;xd zhtw82w b7 :bng faster than the amadx t2/+w7w.y b;hh :8xpzbspeed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 12–34. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device that sends 20,06s u3t*k9)6u ntycip w00-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is d y 63in9up6tkw)*cs tuesigned to work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human3q* tj sldtx:/ audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewer pipe symphony. It con,mq;r- fztqc2z2 g1ca4cre+m sists of many plastic pipes of various lengths, whichg mc,tcr2f e1-caz m;q4q2+zr 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 to the threshold of hue /e1eoy5epw,wju4a w)ew(m;man hearing (0 dB). What will be the sound level of 1000 such mosqui)e ,w1owew e54a u(e/p;ymwj etoes?    dB

  What is the resultant sound level w74y*5 w/ 9 yhviaiyejqhen an 82-dB sound and an 87-dB sound are heard s7av jq/95yyiw he*4iy imultaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 10txch4* g1x1gvww-zg n -(h(2efj k2dd5 dB. What is the acoustic power output (W) of the speaker, assuming it rad v*-g1gj-(k1xwgd 2nz 2tfc4deh( wx hiates equally in all directions?    W

  A stereo amplifier is 9quh*f;y*uyg ;3pu;6m 7ppqqy qq s i*rated at 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. *qmfh u 9qy;u;7 qu 6*p;gqyiy*qspp 3What is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear protective devices over thet3tk*n2vnn3okuw +r ,ir ears. Assume that the sound level of a jet airplane engine, at a distance of 30 m, is 140 dB, and that the average human ear has an effective radius of 2.0 cm. What would be the power intercepted by an unprotected ear at a dist2nn,+r3kv t* u tnwk3oance of 30 m from a jet airplane engine?    W

  In audio and communicatios dat8amz u/j*umk.2: ns 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 tuned to a 8ca5hefj, f.kfrequency 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 fun xdj0 fpt dbes6fx209tfh 1*/idamental frequency of 440 Hz and * dti2f0jh/9 dxfs ex1f p0b6ta 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 waterf 5 gaxidusl n),g3(3z (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 dz(3g f)g3daln,u 5 isxistance 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 mass 2.10 g is near a tube that is opr ;t9cq 4wz 8i 9u:1nn)sh:lqnc6rmsden at one end and also 75 cm long. How much tension should be in the string if it is to 8rs q)lu:t6qzsd c ;9mnnn9c:i rh 4w1produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed t uhlv3(( djf+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 the 500–1000-Hz range comin6 :fkhi,-afve94wwq(g1kjix g 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 tha-kfi kqg1i6 afh xe:49, jv(wwt 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. ,2e)d4va va8m.vhu f qThe conductor on the s8u)vm2v,dea 4ah qv. ftationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approacx-ck+,k8ns0s kk ej y7hes you is 538 Hz. After it passes you, its frequency is measured as 486 Hz. Hjk7nkc s +yxks,08-k eow fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate thamlnu),l w)kh:l(ns (e speed of cars just by listening to the difference in pitch of the engine noi s) unml((lhl wak,n:)se 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 fast is it going?    m/s

  Two open organ pipes, sounding together, produce a beat6j m7 g2. 7wyhove-fpy frequency of 11 Hz. The shor2-.myjo76 ypfh7we gvter one is 2.40 m long. How long is the other?    m

Two loudspeakers are at op cwuh; ftr,dkug;q .7dgk*q8/posite 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 position A, in front of the car, (b) he is between the speakers, at B, and (c) he hears the speakers aftertgf*.qr/g,;dwd u u;k 78cq hk they have passed him, at C?

  If the velocity of blood flow in the aorta is normally about 0.32 m/s what b11u gpo ,l,+8fcx wfpveat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and uwl fp81 ,c,o1x f+pvgreflected 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 fly5ae,91inll eg /2stlv ing toward the bat aat1se5n l,g9i2 ll/ vet speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of the wave detected by the bat after that wave reflects off the moth?    kHz

  A bat emits a series 6h2y l(7ajo ol16qybxof high frequency sound pulses as it approaches a moth. The pulses are approximately 70.0 ms apart, anxoal21 jyh66lq(boy 7 d each is about 3.0 ms long. How far away can the moth be detected by the bat so that the echo from one chirp returns before the next chirp is emitted?    m

The “alpenhorn” (Fig. 12–38) was once used to send signals from ov/v()kj /z ad lf1a ..pu*purfx6kl5 une Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were ul pru.k*vu1.a/f f()vj/u6 klxap5zd sed 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 cansp8v6 xl9jw51;rs zqh be compromised by the 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, and 2.8 m higl1w z65rvspjs qh9x ;8h. 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,38;q; s9thhd1opl arb 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 hbdh89srl;;q1apt o3can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the threshold of hearing for the human ear at a frequw(l9xby nar*ce)4 5lzency of about 10lc*nez4y(rl 9w)ba5x 00 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 ground hears the sonic boo1j5zztcviu;/ w xb:)d 3qb vt9jsk29em 1.5 min after the plane passes direjbb 95zd 1:tcxjvk3)uszqv9 2w; it/e ctly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedbt-b8ijc0rhu , 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