What is the evidence that sound travels as 3w h4h q 1o,gtkwoksb*.3/dd ua wave?

What is the evidence tmaoy014 xpv,1m z,bgphat sound is a form of energy?

Children sometimes play withfvukb6:)w4a, a tw 8kh a homemade “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). Expw,k8u:vha a w6b tf4)klain clearly how the sound wave travels from one cup to the other.

When a sound wave passes fro7j/oi qu w:4bam air into water, do you expect the frequency or wavelength to chj4 biu:/7oqw aange?

What evidence can you give that 064iidl-:rc 7 eyvd)kvj4 d azthe speed of sound in air does not depend significantl0zrddvev-l4i 6i:k jd)yc a7 4y on frequency?

The voice of a person who has inhaled heli1vie2 )vp :xntum sounds very high-pitched. Why?

How will the air temperaturkk3i vca ,jc 2/ lejnj,qy2tql6 7(fqj5 ;li+le in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitud +coim a:f+n*qe of sounds in various frequency ranges. (An example is a car muffl* fcm+ inaq:o+er.)

Why are the frets on a*d w,, ifdfh)-gucq /j guitar (Fig. 12–30) spaced closer together as you move up the fingerboard tfhg dfwi/ q)cj,d,*u- oward the bridge?

A noisy truck approaches you frol(k j ;37 mwqloveyoknlx; -*9m 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 difv3 7 xky; -nllwmo*l(;o9jkqefraction.]

Standing waves can be said to be due to 2x/,(n)ki0fna tbn by1 kdh/s“interference in space,” whereas beats can be said tbd01,()k snhk t/2biynanxf/o be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were 8x ar8s4km :roip o m241r-ouplowered, would the points D8porr4pio8 ksuao2mxr:m4 1 - and C (where destructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who wo +h6 (hrwuo,jbrk in areas with very high noise levels have consisted mainly of efforts to (+hrjb ,hwou6 block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two wav v z.n yn x,6r5bb0w)wtfmvm-1es shown in Fig. 12–31. Each wave 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 two component yx0b )ftvr5zw.6n -mmb1,v nwfrequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer m7 g)7 aujrgs6rove in the same direction, with the same veloc77gug) rjs a6rity? Explain.

If a wind is blowing, will this alter the frequency of the sound heard by a per5lljjjvzv tt* ..fq+o u+*,u hson at rest with respect to thl+ht ,+.uo.v*fut j v lq5j*jze source? Is the wavelength or velocity changed?

Figure 12–32 shows various position ajr(al;2ygkl,t.7 y4riu q y3s of a child in motion 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 for the sound of the whistle?r ra qjy.tk34,y2yalg l ;7i(u Explain your reasoning.

  A hiker determines the length of a lanr/;p/-*tqyav ys7 b wke by listening for the echo 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 7qps/aw-v* ;rty /bny of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side g,; nsm8jsx-mj:w+xcof his ship just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume the speed of sound inj 8jmg+cwx,s:;x-mn s seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wave ea7nr d, -hw28bsx8jdlengths in air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat is drifting just above a school of tuna,2qtfta:xl4 4ig8yuc on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapu4t yl2,8q4axfi: tcg ses 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. dr; s0z9/lhyy28nzlxThe splash it makes when striking the water below is heard2 /syd;890ryxhnll z z 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone stwwb + lo3dvg0 38h+bjbrike the concrete pavement. A moment later two sounds ar+ 3gwb0 w3b8+vdolh jbe 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 n x0 wo17gmlbaa;qqb;d ip 6.y z6p(g23cgz) ymile of distance by the “5-second rule” for estimating the distance from a lightning b07(y;mnc61yqpaadzzx g p;i l3go) 6q2.gb wstrike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at theju s7a* j kfzut/k01u2 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 in :ft;)e a -lkw xkusxi))-i)ddtensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound lev h ;p;azl.(mlji /kn6cel of 95 dB when fired simultaneously at a certain place, whaacnh;l ;(mjl6 kpi/ z.t will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certq8jc;q-4usws / 6e cgm oy5wh,g3bu+ main distance from an airplane with four equally noisy jet engines is experiencingcsjwb3/; cq eu654ohgm8-+u gmq wy,s 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*k 8zf,px9aqn have a signal-to-noise ratio of 58 dB, whereas for a CD player i8* xp fz9aqkn,t is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speakgxyuoss420ijwt+i 5+ ing in normal conversation. Use Table 1250 j2siyot wg+xi4su+–2. 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 strikes an eardrum whose aru4)bbok. v t1iets 1)iea 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 amplifier m6m s gw9gg9/dB is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a logmw9s9 g/gm6 dudspeaker connected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registf(r lys,g6e xgz7 y.p3ered 130 dB when placed 2.8 m in front of a loudspeake,g g7fl y6xs( pezr3.yr 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 differer73g jxj*.yxonce in sound level of 2.0 dB. What is the y3 7gx jrj*.oxratio of the amplitudes 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) by52x-pqjd a:xcmw i -x4 what factor will the intensity xqw-pm-x j5 d2i ac4:xincrease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twice the frequeecg,b -+s. 2z*i8cca cksvso- ncy of the other.-ks bgce os.i v +csc-a28c*z, What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that cordc7vbe h0h-bs4y h0p/x+f-pz responds to a displacement amplitude of vibrating air molecules of 0.17zvh4pp h+df00/cy-- b hexsb3 mm at 300 Hz?    dB

  A 6000-Hz tone must have what x93rds:gmkgpyh x 8 5-sound level to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. 1kr8 dysh9x:pg - gm35x2–6.)    dB

What are the lowest and highest frequencies that an ear can detect when thef8 dzk2u 1mzagp.(u.b sound level is 30 dB? (See Fig. 12–6.p(.1 muz gab8zuk .2fd)

  Your auditory system can acann;-fo60 9 8 nad8zo6bjo ikdcommodate a huge range of sound levels. What is the ratio;d6odfnokai6 bn8az0n8j - o9 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 frequ+(6w od sobzh0hr e0l+k*wa)fency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tensirwdhl boe+)h*f(w6k0os+z a0 on must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first three audibona9czp v a2+2d.kch7 le overtones if the pipa. cp2kacdhz2ov+9 n7e 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 blowituii 4.;f6rw qng across the top of an empty soda bottle that is 18 cm 6f4.iqrt; wi udeep, 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 c 2dowgxm-(1t organ with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengtx2wtocd- 1 (mghs of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmonic. What wilx * cs(jhv msq g)ma/.4i,8akgl be its fundamental frequency if it is fingered at a length of only 60% of its oq cmkv4g(*,mg8aa.xs ij)/s h riginal length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E above midd6s + rrseeuu-;le C r -;6suueser+ (330 Hz).
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that emits middle C rx ue ;*s /9un-u)iqax(262 Hz) when the temperature ii usx-ur/q;9e uxn)a*s 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 ktatgrv-:p40 jio8xh ) ,u5o-3 yqqgk20 $^{\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 u5d ,zd(la0 ) .fn hf6t2gyuft12–10 should the hole be that must be uncovered to play D above middle C at 294 lftyduta265)f (ug ,zndf 0 h.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 reszsru9kdn/b7q ) fu;n8 fbi0/jonate at 264 Hz, 440 Hz, and 616 Hz, but not at any othirf b/jqkuzn0nd; 9b fus8/)7er 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 1.80 m long is open at both ends. It r+sy)h 2xdx(aw 6m( jd0fyxekb2 e1u1y esonates at two successive harmonics 01)x+da y(e2x fy jsbh2dw um6(ykx1eof 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 pg(o0e9 v4qis q;7yxvgszy.-1)yfi q$^{\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 presen+i.:ls sw1 l 7o2qnptft within the audible range for a 2.14-m-long organ pipeqwpfs1:s nito+2ll7. at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open touw/ gj mv+c7hrg(2/hm the outside and is closed at the other end by the eardrum. Em ( 2r7/ ghum+wh/vcgjstimate 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 hw m+qrs.*0t2ueg :jf m:4r gywhen trying to adjust two strings, one of which is sounding 440 Hz. H 0 mgwsr g2y:4.:qu ehjt*m+frow far off in frequency is the other string? ±    Hz

  What is the beat freqiz*h ah8mb nm;6l+ t+mwhb2u7uency if middle 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 operates at 23.5 kHz, while another (brand X) operate xx rz,/47t+emfemyd.s at an unknown frequency. I,4 erx . dm/tfe7yz+mxf 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 brand X.    kHz

  A guitar string produces 4 beats/s when soundedy-t o2c+hlmvuzmdpugc ;m m7 :89z56w with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of tot8y9gz cv7m 6+lu:;cz5mpm 2wmhd u -he string? Explain your reasoning.    Hz

  Two violin strings are : dxbf54w/l- yxht le;jv0(0hqvqwx 5tuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be 5 y-d0q/j5wh:xhle 0 x qxvb;lt wv(4fthe beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be(2e( k)yu e)slg;yyvq heard if two identical flutes each try to play middle C (26)slv;u2e )yk(yeqyg( 2 Hz), 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 frequency of 441 Hz; whb 5fi94gpkjdlqqg 4( ;ds :9qpen A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequepjq 9ddbl9sp4(fqk:g;g q 4i5ncies 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 apa0,kedp jm0.iart. A person stands 3.00 m from one speaker and 3.50 m from0j e0 idka,mp. 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, bib(0k1 joko i:kwr.e4 s)wv+r ut a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, whatw jk+k:owiobk0. 1v(4ir) rse 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 inw uo)0d2)t (rvaix u.k air. How many beats per seconi20w x.)otau uvk(r)d d will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engi*fi ;iqi+g1rw7 da;mja9 lu7ane’s siren is 1550 Hz when at rest. What frequency do you detect if you move with agjuaq ;ilw;9rafi i d177 +ma* speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you dge8o ia.78exaetect if a fire engine whose siren emits at 1550a8 axee87iog. Hz moves at a speed 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 movu9h . .z nb 3xwrf14jit8df,tjing toward you at 15 m/s versus you moving toward it at 15 m/s Are the two fx n 81t4bru.9ji,. jtzfhd3wfrequencies 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/ m))0zgv)1rr ibwo oe is at rest and the other is mvz 0/oo1me) r))bgirwoving 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 wave fn4r2 7omasmcs ,8n8bgw ;4wds at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the received sound frequennwc w4sgfmb nos m;r2d88,a74cy?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flivo*kffb5ywc2, :bj3 w es, the bat emits an ultrasonic sound wave with frequency bc,2f:5jk wwf v bo3*y30.0 kHz. What 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 movf-c lfn g* -5qqc2qd5ring flat train car at a frequency of 75 Hz, and a second identical tuba played the sam 5cqrf* 5- qc2qnlfg-de 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 d s0sny (q3*smokzv y zjww1,fe06 :w2to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in:my2szvko103 jwdy se 0 wzsfn(w6 ,q* 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 away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of freqdi mk.2kx42b yuency $2.25 \times10^{ 6}$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 freio+ 5mnj h dt/hw;;vq.quency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hevmq j.h;d;o iwnt/ 5+har who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object movizim722 mxc9 yqng on land if its 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 tfq-ge *c9 y2)uuox,g ahe speed of sound is 310 m/s (a) What is the angle the shock wave makes waug2 x cuqeoy* g)f9,-ith 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 thmvny y vay,bmjkq 4 k234y()+he thin atmosphere of a planet where the speed of sound is only about4yvy+h,bm )vjmkya2 ( nk4yq3 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 8500caegf8 /u8c j*u*0yqa m/s strikes the ocean. Determine the shock wave angle it produya8**cc/gquejfa 0u 8ces
(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 8m+j3ub n-nxbw k*o)j$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and see a pmx lcr9ee 6/2glane exactly 1.5 km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has t gmc9er6l x/2eraveled a horizontal distance of 2.0 km. See Fig. 12–34. Determine
(a) the angle of the shock cone, $\theta$    $^{\circ} $
(b) the speed of the plane (the Mach number). Assume the speed of sound is 330 m/s   

  A fish finder uses a sonar device that sends 20,000-Hz sound pulses d, ;o0 +q0styt tnm,rcjiod;3lownward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 200 m,r,t0o oli st;0+ y;qtcn,d3jm what is the minimum time between pulses (in fresh water)?    s

  Approximately how many octaves are there in the human audible rabd6d ;4ecye/ bnge? $\approx$    octaves (Round to the nearest integer)

  A science museum has a displayotq ixrv nncf849d -7- called a sewer pipe symphony. It consists of many plastic pipes of var 4f- 8-nnivd tc7orxq9ious 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 to the threshol jxnbn9ht0:kf:n9 w1 :mazbu;d of human hearing (0 dB). What will banh0 bk:zxb ;n:um9n 9 1:wtjfe the sound level of 1000 such mosquitoes?    dB

  What is the resultant sound level when px2ury d32 v2 ctc9io.p7n.igan 82-dB sound and an 87-dB sound are heard simultaneously?39d 2piyctp.. x27gr ucvno2i    dB

  The sound level 12.0 m from a loudspeaker, placed in the opeo be - d rt*5;4x;,toirwszc;an, is 105 dB. What is thidra*4;o;r e xw , 5bt;stc-oze acoustic power output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rateoh 3u9iv ic9grx (b*c8d at 150 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the pour 3bcc8g(*i9vih o9xwer output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wear prote(nxt9e bqtns6f) qf5b t *l17rctive devices over their ears. Assume that the sound level of a jet airplane engine, at a distance ofteq 9 fbtq b*5)ntx17s(l nrf6 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 sbq6+ 3; ux24 cyc ve- nu.n0rlllwox:tystems, 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 frequenck2n)qesbsip ), 6 q+rorw1s.fy 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 loxv)6fm 8vc; on)b6y qeng between fixed points with a fundamental frequency of 440 Hz and a mas)nvmf )c686 xyove ;bqs 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 aq9j 9 el9hai mn9vv 7sx0;zq2n:q3isqbove a vertical open tube filled with water (Fig. 12–35). The water level is allowed to drop slowly. As it does so, the air in the tube above the water level is heard to resonate with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning f9 2;lqxmqez hins j9 in3 sv7qv09a9q:ork?   Hz

  A 75-cm-long guitar string of mass 2.10 g is near a tube that is opguq.3jif7ne k /ohl7l 519owp , s0lacen at one end and also 75 cm liwqo, clg7 hf 1le5s3 u0.9k7opj/anlong. How much tension 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 observedv,-o) ol 98ti;loz om c)kt:xv 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 500–1rgog s24(xlyv* t0rs.k: i ns+000-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 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 frequeyr(.4svi k2nxs: l ogg0 *t+rsncy of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The conducto ( (4 z: dd;;fzfpspovtpybz//+kp tu-r on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What is the speed of the moving;s vtpz4;b- (dpp/ :ydf/t+u f(pzzk o train?   m/s

  The frequency of a steam train whistle as it approaches you is 538 Hz. After itzvp6/4 p3 ;vsk r;lelr passes you, its frequency is measured as 486 Hz. How fast was the trainvl pr3kp6;r / e4slv;z moving (assume constant velocity)?    m/s

  At a race track, you can.slp9/a acdr + estimate the speed of cars just by listening to the difference in pitch of the engine noise between approaching and a.s/pc9a r dl+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 beat frequenr n nk/44d*gu+n*yohj cy of 11 Hz. The shorter one is 2.40 m ludno n hkr*4 jn4*+/ygong. How long is the other?    m

Two loudspeakers are at opposite ends of a railroad car :p jakgf0rp h. )g5dqyg)y.)l as it moves past a stationary obserg) dyj )h fp5qag:prkg.0 )y.lver 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 after they have passed him, at C?

  If the velocity of blood flow in the aorta is normally about 0.32 m/s whauv+ opf9b02dm t beat frequency would you expect if 5.50-MHz ultrasound waves were d0+2fb9vdoum pirected 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 flying toward the zswswd s,c-8+4 : x:nsmb0wbybat at speed 5 m/s The bat emits a sound wave of 51.35 kHz. What is the frequency of the wave detected by the ssb+b-:0xndsys ww:w,4 mz8 cbat after that wave reflects off the moth?    kHz

  A bat emits a series of high frequency sound p1ih 8nkmmuqps q5e me k;*:u4+ulses as it approaches a moth. The pulses are approximately 70.0 m e*ie1su5u4mq knp;k8h+mm q:s apart, and 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 , ck 5tfbsxq ch7r:a:,from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one 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 rk ,:tcfc q57xas ,bh:of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be compromised by the presence oq18ei 1z0lxt af 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 8qz1t0eax li1high. Calculate the fundamental frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, calt9(k v4gt xp3rled “singing rods,” involves a long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With9t vx4tr3gk( p a little practice, the rod can be made to “sing,” or emit a clear, loud, ringing sound. For a 90-cm-long rod,
(a) what is the fundamental frequency of the sound?    $ \times10^{ 3}$ Hz
(b) What is its wavelength in the rod,    m
(c) what is the traveling wavelength in air at 20 $^{\circ} $ C?    m

  The intensity at the threshold of hearing for the human tos t; rsu 5x f-;6dt7gen+)ykear at a frequency of about 1000 Hnudt ;tsx6+e- o 57;kt) yfsrgz 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 travelingpurupvo0 -77c7 3x7pbcb qm u: at Mach 2.0. An observer on the ground hears the sonic boom 1.5 min after the plane passes dircvp7 p: u7 7 obcp0-7uxbr3muqectly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is cp2e.n xsu +*6camc5)t+x f -eca4 lrs15 $^{\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