What is the evidence that sound travels 94kw :oi;plu)gms(pct -6kxonzi 4+ bas a wave?

What is the evidence that sound is a form of energy?d*l7/be-rwd0smjyb 8c 5 i/fp

Children sometimes play z1ud -s.z)6yeo*5 q hfjv-qakwith 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). Explain clearly how the sound wave qy*ej-z1)5saq kdu v .6zo f-htravels from one cup to the other.

When a sound wave passes from air into water, do you expect the frequency or 06wh x3;mhllen,ix,cwave xl,mhlc0w6 ie;,3hxn length to change?

What evidence can you give that the speed of sound in air d.938 vjfyukbc9(fk sh iul*o/oes not depend significantly on freq9j h8u3/f. 9ub(siykfvclk* ouency?

The voice of a person who has inhaled helium sounds very high-pitchezpd*4z2b-8scgh r7 fjd. Why?

How will the air temperature in a roo mw+32f vl fcygksq6k 10so60tm affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude of s3ec jx0 z/.pinounds in various frequency ranges. (An example is3n x/ei0pjz. c a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer to*nroay*ckj)ywy, rm-+y m22 sgether as you move up the fingerboard toward the bridge?nyc o -s2+yj2,kwym*)amy *rr

A noisy truck approaches you from behind a building. Initi vkb9d6.3soiyt p:ny*ally you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “b9sd ikp v*otn6by .3:yrighter” — 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 “inter4cvrfvu3,9 -q pjq1zz ference in space,” whereas beats can be said to be due to “interferjv p-cr 391zq fuz,q4vence in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the poiny47a cpe9cd(mp x(meh+3n*dfts D and C (where destructive and constructive interference occur) move fartherd+3ecfep9 m*7(dhp4 c(yxman apart or closer together?

Traditional methods of protecting the 9pie5 gh+ azz;hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could gzea 5 ip;9h+zadding more noise reduce the sound levels reaching the ears?

Consider the two waves shown intlb wtlng7 -:vo p1s4* 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), arel4sg*tnw71 :b tl-ovp the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if thq .pz3.spx:dke source and observer move in the same direction, with the sampd sz3pkq:..xe velocity? Explain.

If a wind is blowing, will this alter the frequency of the 0(tde y7,+qy0cenwzmg*d su4sound heard by a person at rest with respect to the sourc d gm0wye(+n*,s uy0zc et47qde? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monitoru6(, y.:k9rfeb b;fc xqnm;su is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear the highest frequs6cf.e:r9x;, b ykbnuqu m(f ;ency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length ow:hw:u ja7p tivoq c,-04eiy1tw7m.wf a lake by listening for the echo of her shout reflected by a cliff at the far end o4. -jcw7tohq apy:0w1 ,vwe : tw7imiuf the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the si3thg18 wc .zihde of 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 in seawater is 1560 m/s (Table 12–1) and does not vary significantly ci13.hhwz8tg with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air at 2 ;ilik; 0aff*17.u 5vn 5l kzoyyl6dxn0 $^{\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 js33w 2z ymoyi4ust above a school of tuna on a foggy day. Without warning, an engine backfire occurs on anotherms43z23 yoy iw 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 miva-ox- 8e)iosw4j6splash it makes when striking the water below is heard 3.5 s lo-m8v e46ixioja- ws) ater. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strimbx rh m1kfxr t4s47)+z;j a2vke 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? See Tak4;zra h msr 4jx xbt27v)1m+fble 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance 1 96dwm -eqrrwby the “5-second rule” for estimating the distance from a lightning strike ifd9wq6m rre1-w the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 1k)dcvfwp3fd; ed6 )h/20 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 soun jzr0*s bd)v5ad whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultabk:rhbjasp l43 j ;- ewu66l6zneously at a certain place, what will be the sound level if only one is lsz r6b-kje66j:l ubah;w43pexploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain dista;mtzc o2 3 ,5pm,cbaprnce from an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut down alabzr o3mc,2p; ,tmpc 5l 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,1na yfx4pi5f 5 whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the bac1nfafpi x554 ykground noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a peus 0fto 6cin vs.qlmn9*n*0b* rson speaking in normal conversation. Use Table 12–2. Assume the 06n u b*tl *ofvi90q.mc*snn ssound 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 ear8 *u ltdy1n0e baaz:0fdrum 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 amplipp-tmak-1 t+ t4ii0ef fier 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 to em+ ft-kit0 p eiapt41-ach 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 register0ck*udg u -xk6qd+u0,yhrix.ed 130 dB when placed 2.8 m in front of a loudspeaker cg- d0qhxu0k. i6 rd uxuy,k+*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 typicemjz, 1 0por1esh1(ua ally detect a difference in sound level of 2.0 dB. What is the ratio of the amplm1, he0eur1 ( oz1jaspitudes 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 v7wfv5aj,q 5x7y)hd o zq: 7vswhat factor will the intensity increase? Increase by77, zo: qa )d55 swxfvhvy7qjv a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twicpp3g8 vw7yo:1w yqo3 ne the frequency of the other3o3yynpp 8 wwo1 q:7gv. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that cors(r u xh./jv,rresponds to a displacement amplitude of vibrating air molecules of 0.13/,vjhr su .x(r mm at 300 Hz?    dB

  A 6000-Hz tone must he: 8)ks18g,rcw clvk qave what sound level to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. 1r 8gv ,8eqlw):cc k1sk2–6.)    dB

What are the lowest and highest frequencies that an ear can detect 1+ rmax)p8t xbwhen the sound level is 30 dB? (See Fig.abrxptx 8)1m+ 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What x7mzr,sa3w5k is the ratio of highest to lowest intensity at w xrz7ask3m,5
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental frequency of 440 Hz. The length oi xdom,n ntb)hhgo-4*t70 (vm f the vibrating portion is 32 cm, and it7o og)ihx0 mtv m4t(*b- hnnd, has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first three audiblxd92pr. : eu :wcaj;sqe o s.:x:acdq jr;ewu9p2vertones 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 frombog*p e*q 7zy. blowing across the top of an eyg*.oz e pbq7*mpty soda bottle that 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 the range of hus7h 1v( era :ep-1svdjman hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes requse1v e7sah1- d(v pj:rired? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency ofh(0vv-y 7m09xpkkguz lsj)a, 540 Hz as its third harmonic. What will be its fundamental frequency if it is finges7 yh zlav,x pu-m(g00jk9)vkred at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tunedq 0e x+ whd v9v .;lbh-l6fmdi0obj j:2bzd,*u to play E above middle C (330lie9,jdbh-o6wbdfm . 2lju d bzq;00v+xv :*h 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 orgmt)03h;qc+vxlsg :kvan pipe that emits middle C (262 Hz) when the tempe ) vhv+t0q3 kmxg;l:scrature 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 zii e zihxq*+)n7c37v20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Examplqmzh+87 j8(ev(tlc zqe 12–10 should the hole be that must be uncovered to pl( c 7zj8+ 8(lezqmthvqay D above middle C at 294 Hz?    m

  (a) At T = 20 $^{\circ} $C how long must an open organ pipe be to have a fundamental frequency of 294 Hz?    m
(b) If this pipe is filled with helium, what is its fundamental frequency?   Hz

  A particular organ pi5 lgydtbi 82z4j 6z;hxpe can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or a cl5gh24 zbitl;yjx68z dosed 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 ag d*orl4-p9z1syrc j1 t two successive harmonics of frequencies 2p- *syolr c14z19jrgd 75 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 ;bxx tne4l48t$^{\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 9o,qnqr cj5l*; 6eipd organ pipel*,jr ;npq9q 5i ocd6e at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is appr--i od1ukmq7e oximately 2.5 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 relationudi m--7oqe k1ship 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 e4 me3p5-1faw. zn qskrvery 2.0 s when trying to adjust two strings, one of wwanpe fsr.z513-mk q4 hich is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middlebod4z7vpjl . 2gy ijj-jsm35: 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 (branmq+ (hmlh 8 wbc -r0pa9tn1zo,d X) operates at an unknown frequency. If neither whistle can be heard by humans bmo1a9np(0-mh w8r,zqtc l h+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 wh1gmlqnm4*b,x)t6 hxjen sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational freqqmjtnx1l) ,4 h bx6*gmuency of the string? Explain your reasoning.    Hz

  Two violin strings are tunei z*5mc7-z tpzd 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? [Hint: Recall Eq. 11–13.c7*5 ziztpz-m]    Hz

  How many beats will be heard if two identical flutes each try to play 819sha7txyh( qevis3(i h zx *middle C (262 Hz), but one is at 5.0°C and the other ytq97h31xihs a sixe8z h*((v at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Hz; wh7gstr *,.iai, o fji6hen A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and7gf .,6 jah,risot*ii 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 m7sk,4b:azmu b from one speaker and 3.50 m from the othbmz 4a, ub:k7ser.
(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 vibratingd7l p2 see mdd6u dur6kw1(7pdw95 wh.10msl k at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hzl des 1 (wsep77m5w.dmduh1k6w d kud9 l6p0r2, 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 aku)t4 45idwqhu +q ;pper second will be heard? (Ass tukq4ai 4;+uhw p5)dqume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fq0a.ro tt4c+lire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30qtac 0.o4lt r+ m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you diul rwylzf7h3v+ ; z24+z2ys wetect if a fire engine whose siren emits at 1550 Hz moves fi szz2wyyl4z2 v+ 3+rulw7;hat a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hzuy + 3 xe95b. lrvomsk;icm;r6 source is moving toward you at 15 m/s versus yous xevm r6b;c+9iyol.3 mr5ku; 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 equiqzikf+i1h*x (hj :ma9pped 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 frequency the horns emit? Assume T1mz* fxik+h9(jqiha : = 20 $^{\circ} $C    Hz

  A bat at rest sends o1jtp36u d/oq z)*s dfllp .n5yut ultrasonic sound waves at 50.0 kHz and receives them returned from l6tpz sn 5p*yd)uoq/l3f1dj. an object moving directly away 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 emits an ul.)j0 qli9whdltrasonic sound wave with frequency 30.0 kHz. What frequency do0.9 djiqhllw )es the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler expericp11 spte6jd 8 /in0faments, a tuba was played 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 1idnt1 c seapp8/ f0j6station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow md d3yfj)h9b5 speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human )9 3mhyb f5djdtissue 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 frequencyi j(5jwa btm.0 $2.25 \times10^{ 6}$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 the wind zfuv7cgyv/bxh;v*o qp1 sa-,/+1m mx velocity is 12 m/s from the north, what frequency will observers hear who are z7b1xs m+y, q/ vfv vgmp-uao*1/;chxlocated, 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 (n1f4(5pljm wk7xdmsh6r7sj 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*a+cgpz;j ge (z1v5z rsna5+ t Mach 2.3 where the speed of sound is 310 m/s (a) What is the angle the shock w (a ;+gc5t+zjsvpg5r nz 1z*aeave 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 atmob5+ .kqjp*a cl c3ry3ssphere of a planet where the speed of sound is only bqscy5cpr j3ka3*+.labout 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 strikt c.a)*c9ospies the ocean. Determine the shock wave angle i poca) c9t*.ist produces
(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 2d dtb duinxgb3:to: ,.,fu 3f$/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhr+( v -(i6iltoid gkb1mstx-yf+h57 iead and see a plane exactly 1.5 km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal dist6+ (gv-lk5dxtty+ soi( i7 im1h-bfirance 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 downx9k.s 8 t*(og9 obkjp n*er6rgq+3us dward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed tej**og+b3ds 8n k r qog sp6kx.tu(99ro work is 200 m, what is the minimum time between pulses (in fresh water)?    s

  Approximately how many/,lu+1 f 8ulnmbk 6nva octaves are there in the human audible range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a display called a sewe hd/rpoz5w w:o9bwxu,wcy2(q )mj p*/r pipe symphony. It consists of many plasm/p5x,db w92:p( *wo /cr z)wq oywujhtic pipes of various 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 person3 ()zzz:oqhxc makes a sound close to the threshold of human hearing (0 dB). What will be the sound level of 1000 such mos )3xzoqh:(zz cquitoes?    dB

  What is the resultant sound level when an 82-dB soun zdu7kr 9p36und and an 87-dB sound are heard sind9zu63kupr 7multaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is 105 dB. Whaa/*5lsut an,vd/ y/ rkt is the acoustic powr/tkuv ds,5l a/an/y *er output (W) of the speaker, assuming it radiates equally in all directions?    W

  A stereo amplifier is rated at 15*:d o tqmh1q6 e.i2bfv0 W output at 1000 Hz. The power output drops by 10 dB at 15 kHz. e*h.i6 ob21dq: tfvmqWhat is the power output in watts at 15 kHz?    dB

  Workers around jet aircraft typically wxnc6bq+/2yb)y4 d idiear protective devices over their 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 woy4d+cb2i n/) b6dix yquld 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,,pg4 cmsz0jsluuq ,34 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 frequ kb x/05crwl7 e +o96cbq+vijgency 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 po5gj o;7c r)rawints with a fundamental frequency of 440 Hz and a mass per unit length of 5r caw);gj7or$6.1 \times10^{-4 }$ 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 vertjfj0i:o f+.wtical 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 fi. tjof+:0 jwis 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 ma,wnl:lmql 71tss 2.10 g is near a tube that is open at one end and also 75 cm long. How much tension should be in the string if it is to produce resonance (in its fundamental mode) with the third harmonic in the ,q:tll7 ln 1mwtube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonathwsl6sp. b pv4 v;3)one as one full loop ($\frac{1}{2}\lambda$) when a small earthquake shook the ground vertically at 4.0 Hz. The highway department put a support at the center of the overpass, anchoring it to the ground as shown in Fig. 12–36. What resonant frequency would you now expect for the overpass? Earthquakes rarely do significant shaking above 5 or 6 Hz. Did the modifications do any good?

  A person hears a pure tone in the 500–1000-Hz range coming fromag 9h+wq6hfqnjc;9( qrl)k2d 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 levg2c+rqq(9jl hka 9w;)n6fqd hel 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.z-qt.-efup)c9v:c za One train is stationary. The conductor on the stationary train hears a 3.0-Hz beat frequency when the other train approaches. What qz.cv zfeuc--t )pa9: is the speed of the moving train?   m/s

  The frequency of a steam train whistle as it approaches you is 538 Hz. Aq3kgx 6j f ye+26gm9dhfter it passes you, its frequency is measured as 486 Hz. How fast was the train moving qdxj6gfg+ek6m923hy (assume constant velocity)?    m/s

  At a race track, you can e1h+ue e8j: xnn-vee4 m/qij)d stimate 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 fast is i48 v1h/nxqi -enej:+)jued met going?    m/s

  Two open organ pipes, sounding together, produce a beat frequency of 11 Hz. Thvzc*c rh5 e/b 7g6-xxj8+djjhe shorter one xhj-/z7 * chcjbx 5jr6dg +e8vis 2.40 m long. How long is the other?    m

Two loudspeakers are at onj5 pjyb9oz x,oiz9*: pposite 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 aftejyzxj ,zp*95oi obn :9r they have passed him, at C?

  If the velocity of blood flow in the aorta is normally bg; /ype1 7)pcu6tcsz about 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flow and reflected from thzpc; t p/c6)1y7bgusee 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 )5y jedjb)4c d5h8 vfnmoth is flying toward the bat 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 bat after that wave reflec5hy jd) bdefn)8jv45 cts off the moth?    kHz

  A bat emits a series of high frequed-lv 0i.tam;df ib/ i(ncy 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 dli.d-m ;vf0ba iit(/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 one Alby. b hj(8zbbm7mk:n.pine village to another. Since lower frequency sounds are lesb bmbjz:h 7.bky8.n(ms susceptible to intensity loss, long horns were used to create deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundamental frequency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be compromised by 5xnda 9ushf- 6 zn8ah*)gim5tthe 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 highfa-inszx h 6 a)un*gm 5ht89d5. 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 loni .x9 ogiwa-/exe9 buv-ef) k;g, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand.xu;gibvi9eeo . x/)- a9 -wfke With 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 ear at a mzeac;plq +cz0/n. ,nw uk/6l frequency of aboutcwa6,u0 el //+lnc ;zkzqnm .p 1000 Hz is $I_0$ = $1 \times10^{12 } W / m^2$ for which $\beta$ the sound level, is 0 dB. The threshold of pain at the same frequency is about 120 dB, or $I$ = $1 W / m^2$ corresponding to an increase of intensity by a factor of $10^{12}$ By what factor does the displacement amplitude, A, vary? 10$^{a}$ a =   

  A plane is traveling at Mach 2.0. An observer on the ground hears the -i6 bnq pl*ufci ,lo;4.roj; hsonic boom 1.5 min after the plane passes u; ;o* po6clijfl h4n.-rqi,bdirectly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat d1v9i dzvc:o(-lv e(vb8sq4rlhu zl;f8( x/pis 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