What is the evidence thamux 5(c -5*hv:yc5lvgjly *vmt sound travels as a wave?

What is the evidence that soun408eb9ga5oha 8dyzjdd is a form of energy?

Children sometimes play with)m mxv w-t 9+df7d3gdo 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 -tm)+d3d7d fvmg 9w oxwave travels from one cup to the other.

When a sound wave passes from air into water, do you expectomp1,w c ijg0 up8:b*q the frequency or wavelecu0p8m*q1 bog,jwp :ingth to change?

What evidence can you give that the speq x -2gmk9uf:t njvf3-ed of sound in air does not depend significantly onv mfng39ukq2-x-jft: frequency?

The voice of a person who haslvw fj;bbwsm47+wy 6r 1nr zb72j2mvzm+ or8* inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch ofoyznbkngb.k *r011 :vx .z r5g organ pipes?

Explain how a tube might be used radai6 : zztsh*j s+/z q: cpzq.g(8,q6:knuhas a filter to reduce the amplitude of sounds in va qng/c *rs, 8q6jz(:hz+pihzkaz. d a:6 tqu:srious frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closef r/ vt9c3ddf/r together as you move up the fingerboard toward t fd3t/9f rd/vche bridge?

A noisy truck approaches you from behind a building. Initially you uyd:9ldb 3jd 1kl;il io,-my/hear it but cannot see it. When it emerges and oi9djyly3 b ,u: ddklmi/1;l-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 “interference in space,”yia3 1pa29,xng zoq a761cha js0at;i whereas beats can be said to be due to “interference i0pjya,a1ha n19 i72; ogqt aa6sx3zicn time.” Explain.

In Fig. 12–16, if the frequency of the speakers wel ( z;a-ml zbp u6hko+3pwz:hjv (xo5k7y o,;wre lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or closk uljzmaz: +kbo(;,6poh(p7;wo vlxz 3y- hw 5er together?

Traditional methods of protecting the hearing of people whoqy -u ;fz:6zhiosr4uh :x.hq. 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 devicez6uh iuqz-yr xh qo.;s::.4 fh is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought of as xxo +d5x: 5a-c/a yabip pbx/: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 /c -:pi+5 px/bx5xyxaaa :odb frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the souzxhp)+izen o3 m:- x :*ih,yayrce and observer move in the same direction, with the sam+,hm ap3i:xx*en)ioz hy:yz - e velocity? Explain.

If a wind is blowing, will this alter the frequency of theao; 8qhfdfxkmi 8 ;bnsg+f23/ sound heard by a person at rest with rgm2xb/f8 d8fkhq3oi +sa;;nf espect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing.-guw2+ 6vo rhzh68 snt A monitor is blowing a whistle i+vhtho u8wz gr62n- 6sn 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? Explain your reasoning.

  A hiker determines the length of a lake by liawf0nw50 .sjavqi 1vkvg5/q+stening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake.n kq q0v.swiavw /50vgf 51j+a $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his stn sv/ l-qxid*wzu1-q jo5z; ,hip 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 with depd-uo ,-j/q xz*;zstqln 1iv5 wth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths ixviv )o789n lwn 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 ofs 8e62u9zt6um jciub f uz(we 8,ec-5y tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before mzwy cieue8zfu 6,utb9j8(es -u c625 the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes when strixz tcg8n827 wkking the water below is heard 3.5 s later. How high is the cliff? 2g78tw8 nc zxk   m

  A person, with his ear to the ground, sees a huge stone strike t0llbqu-wnd vli y 9- 523y0lrche concrete pavement. A moment later two id-r2ull vb5ly0ywc 3n0-lq9sounds 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 distance by the “5-secont mhss9q;dk43 fu -1dvcu(qcr ,1aw-wd rule” for estimating the distance from a lightning strike if the temperature is ( vwt1 ds-u1 s,cuc;w(ka4 m9-f qd3hqra) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 120 dB.qx5 tie)0(fqfsji *i( t;awv?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level 8v73l-s xfj3u ee1k+jqq j zc)of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaf :1.ndw. repb-815ahxmju:dzhcrz2neously at a certain place, what will be the sound level if only one is exploded? [Hint: Add inter :fdub cxn:h-j m1dzr.52paw8e 1z.hnsities, not dB’s.]    dB

  A person standing a cer7 wy lgzy28:bc 0 ivs1(bqa:gcb8oj7htain distance 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 all but one bgc2sh7vb0z1( 87ly8q:cg iby j:wa oengine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to ha18 z7ylqvckz 3ve a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for e cqkl8v173zy zach device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the pow be0u6dcs9b rn+lam; 7er output of sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere a dmb6+eburc7;ln09 scentered 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 strikedrf9eb /n kg;*s 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 25z; c(+s4z vona0 W, while the more modest amplifier B is ratedna v+sz;zc(4o 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 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 ajv :d/,inhegj-p g 2:m o8f9odB meter registered 130 dB when placed 2.8 m in front of a loudspeaker on the go jp- m9 /fvdgj8e n2,oaih::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 s,x e po;d,0vo4,kn wlf (pvwv:ound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levw; (d xpk0on:elf,,4 vvw,vopels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what ffsq1jses9l: s (x vz9- kkwr)x.vcr)/actor will the intensity ins:1s.rj lzk x)qf-( e9svx9wc rksv)/crease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, butjwpotvg(cn o;;+v;7 c 3j-jcmj w8xz7 one has twice the frequency of the other. What is thej7+-n7;3 ztc8m;xvwc wjv ;gjo ( ojcp ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that correyot ulp ;-bv(0sponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 300 H0;(bu -vlt yopz?    dB

  A 6000-Hz tone must have what sound level to seem as lou3 qlq4iht*.7avj j( kid as a 100-Hz tone that has a 50-dB sound level? (See Fig. 12–hi q47(*ljj.ti3q a kv6.)    dB

What are the lowest and highest frequencies that an ear can devo,j6x.; -2x:2ddjo uzka azxtect when the sound level is 30 dB? (See Fig. 12–6.) zxj;akod2a 6uj x,: dz-.2 ovx

  Your auditory system can accommodate a huge rangn)ei h lw5 p b(ym22w+ljud6j;e of sound levels. What is the ratio of highest to lowest intensit2jwup(i2+l y) web5;nlm6hdj y at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violigwp:50iqagk ,n has a fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a g: wkq ig5p0a,mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fungn,s5 ouqs )(m: jer9ldamental and first three audible overtones ilms )n9,e5(oj: usgqr f 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 frequeh rs* m p;nyc64eunt(xbelvek;7 l;7:ncy would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, ; s6 m;rn7; nkyh*le ep74u(betclxv: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 pip+d2cla 2d nu*le organ with open-tube pipes spanning the range of human hearing (lula2+ nc2d*d20 Hz to 20 kHz), what would be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string pv7eri )3;qcbu.k +1:un pvg shas a frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is finipkq cg73)u1b.e ;srv+vu:p ngered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E above midd k h.lqy j rlwmlw6r9d4 t:2 .pg2+fan5xio0y/le C it.5w0rl g:k2m xq. la64d2/wn fjyr h+po9 ly(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 . .owljoxxzw, vc,7hgce2v:d9bqh6 + (262 Hz) when the tvbx6woh:.9le jdhq ,c., gc +ox72vw zemperature 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 aw3 0dl g9ko jd9h*l i86c/ldnkt 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Esa.b 5vz8 eg/hxample 12–10 should the hole be that must be uncovered to play D above middle C ateaz hb5. svg/8 294 Hz?    m

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

  A particular organ pipe can reqk (tn yfabrai+0aykwlx,.:-: y) 9wm0 xbcg0sonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show 9 kyiqa :c+-.aw b)0yxy(wan t0 gxb:rfk, l0mwhy 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 1.8g1v.l4c e4wgf: ph+lp .s94t )ptsiqq0 m long is open at both ends. It resonates at two successive harmonics of fspcspql41i hvw+ :44 9qe.) t. tgglpfrequencies 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 c2;;ov.c ihjo1wrn8o $^{\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-lj*fkm,r u,ump21 k5it ong organ pipe at 2u, itp5j*u kkf,1mmr20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 +5b1 n5kppv6-ielft o4sn 79vbwqr:p cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of your answer to the informatbe brqv lo7ifpv4ts5n:n 659wkp-1p+ion in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to adjust two4dpq+adkexuc,j v33 / strings, one of which is sounding 440 Hz. How far off qveu,3+ax4 cpd j/d 3kin frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hzy lsu,2- )h-hmst(0dbzuu5z m) 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, whsxdi (9 ;orx2r-s,xn/8t8 m7ykieczl ile another (brand X) operates at an unknown frequency. If neither whistle can be hkczimx, rsi l;dor 8y2n-/x (7t8e s9xeard 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 sound/6y pzx- abi3jed with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz ty /z-jibaxp36 uning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 29i.2j2y8j bro z4 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 to28z.o2 y jrijbgether? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be y auc :n+vu)jxe961y4xumzi;heard if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°Cn9x6 y)v1u;c j4ziea:+u uxmy and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B ha 76 cdru-naijt8s-zeea/ c*5ns a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencieeed/c cu5s7*-az86rna itn- j s are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A person stands 3.00 m from one speaker andf 9yyh *;yyt;m 3.50 m from the otherhy ft yy;9*;my.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed to be vibrating at 132 Hz, but a piano tuner hea7muceyp/a x1(zu) yfs m2 )v8qrs three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the v ypq)s e/c(fmuz2 am7u8)y1x 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 pk)x56m kr *ghbp 2hl)/ab(o xder second will be heard? x/lhmgdhpxb*kra k5)6 b )o2((Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a b(, ib bxf+hi59cpl0ei(v 3 xocertain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30 m/s9e,pii +5((hfb l v xcxb03boi
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do yoq(gkj oc -sv.-u detect if a fire engine whose siren emits at 1550 Hz moves at a spe j-oc.svkqg(- ed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000o+:b4lytx oi1nj :u-u-Hz source is moving toward you at 15 m/s versus you moving toward it a41+yu: -jutoxl niob: t 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 .ig s9(pe9ku*l/ 5h fuge hx(iequipped with the same single frequency horn. When one is at rest and the other is movi i9ehlsgef huu(k9xg(*.5/ping toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0cv;6k6qolo8q omkp5* k+jb4 u(zs ,vqrya00r kHz and receives them returned from an object moving directly away from it at 25 m/s u60smql(+v4*6pbc8q,a vroky5rqj k z ;oo0kWhat is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed oym9 i8 a,/kjucnf 8+unf 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat ujf8kny8 9ac, +um/inhear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving flat o lpser5; r+f1:c xul6bjp2v6rg.k 1 rtrain 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 waespr5c1rgou v6p+b j16 f l2:.rlk;xrs heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to cd( 0e gsft6y( t2;wqpmeasure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat frequency if blootec( w(f ;qs0gp 26ydtd is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of fru6bqow(g(zq 1a8a1 urequency $2.25 \times10^{ 6}$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 frequenc *.mysp mrdv *i-+i/gzy 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observerms * + vdp/i-my*iz.grs hear 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 moving on land if its spn 01vy47uvi d144*kh+hxazvyvtuf1:d gq; e ueed 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 speed of sound is 310 m/8 o1mcfp;tvytj7p q3 h.g :ge+s (a) What is the angle the shock j tc1 3p+gt vpoem;qh:.8f7ygwave 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 atmosphere of a planet where d,8:lolg v q0ithe speed of sound is8 q0 lo,lv:igd only 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. Determine the shock wave angm6p-9rkt )(y ogbn3jhle it producey-6)k t3r bh mgpo9j(ns
(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 n2ff bou6(qe-r6k ew0 $/theta$ a sonic boom makes with the path of a supersonic object is given by Eq. 12–5.

  You look directly overhead and sesiwr t5e p ;w1- 5;3kmr mnd:,eeey*-og)asnfe 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 distance of 2.0 km. See Fig. 12–34. Detere3t-mso)5y;d pwfkrws:-1mg ,ee r 5*nni;e amine
(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,mucbkv*1/g pqn9kd c;.(2eufg qv4x /000-Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 200 m, what is the minimum time between pulses (in u/kq vu2c kb9;c gxm1 .4ngfv(qe* pd/fresh water)?    s

  Approximately how many octaves are there in the human audible;f xo0n auu:ump ::;6n rrc7+bedeov/ range? $\approx$    octaves (Round to the nearest integer)

  A science museum has a displa/ )fgaq1+q xfs1dbx i;y called a sewer pipe symphony. It consists of many plastic pipes of various lengtfs/b+diq ;a) fxg q1x1hs, 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 p o,eje;j2vf.v9lvci4erson makes a sound close to the threshold of human hearing (0 dB). What will be the sound level of 1000 sucl fve v,;e ovj92ij4.ch mosquitoes?    dB

  What is the resultant sh1vxa *:d/ p . osrj59tn,hslaound level when an 82-dB sound and an 87-dB sound are heard siph/9rad 1*,.njss al:ov5 h txmultaneously?    dB

  The sound level 12.0 m from a loudspeaker, placed in the open, is z3(9ypis b01fy).vfkbrkm)x 105 dB. What is the acoustic power output (W) of the speaker, assuming it rrybyxfszbm 9.ki0)(3 pv k)1 fadiates equally in all directions?    W

  A stereo amplifier is rated at 150 W ouu9d 0di(6 vzbvb/sfq*tput at 1000 Hz. The power output drops by 10 dB at 15 kHz. What is the power output in watts at 15 kHz? bu vb/sqz6d0* (v9idf   dB

  Workers around jet aircraft typically wear protective3 nwab q(-50gv hjkv7 nzmm-z- 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 radiu(7hma g-5z znvqmwbv n-k-3j0s of 2.0 cm. What would be the power intercepted by an unprotected ear at a distance of 30 m from a jet airplane engine?    W

  In audio and communications systems, the-c0xun5fyum;0ol o+ l 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*j -fy:gm8dufsj yok8 yv4b::ency 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 y z 4v:4ayov6o6vy5tl32 cm long between fixed points with a fundamental frequency of 440 Hz and a mass per unit l6 y44oyy5vv:ovtl az6 ength 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 la p+v1ye;.zx t+33 .ueyynfqxsa.r 5vertical 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 resonatayf+ 3u.e+x5x1 try.v s zaqnpyl e.;3e with the tuning fork when the distance from the tube opening to the water level is 0.125 m and again at 0.395 m. What is the frequency of the tuning fork?   Hz

  A 75-cm-long guitar string of mass 2.10 g is near a tube that is open at hcysv43 9f -v5fiuijg(f/j,done end and also 75 cm long. How much tension should be in the string ifv-yf ijijg4hdc,vu9/f (35s f it is to produce resonance (in its fundamental mode) with the third harmonic in the tube?    $ \times10^{ 2}$ N

A highway overpass was observed to resonate as one fullg z v8))9.c. ylb3ncx9ecx baq 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 thehoqd0mz c+w. uopmxq +rwud9:0gm a9roq - +*) 500–1000-Hz range coming from two sources. The sound is loudest mwr ++qd.duwom orq+g)cm: 9-* 0 qap0u xozh9at 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 frequency of the sound?   Hz

  Two trains emit 424-Hz whistles. One train is stationary. The conductor o kx(n 8 rhui16ogvckai+* 1tk/n the stationary train hears a 3.0-Hz beat frequency when the other train apc 1k 8kv*khunxgr(+ i/ 6ot1aiproaches. What is the speed of the moving train?   m/s

  The frequency of a so g:t0es;h f5steam train whistle as it approaches you is 538 Hz. After it passes you, its frequ;5t:g0s s ehfoency is measured as 486 Hz. How fast was the train moving (assume constant velocity)?    m/s

  At a race track, you can estimate the spi;;ywxt9bh lt d5 b+h1eed 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 ot 5bybd;1 l9t;ixwh h+n the straightaway. How fast is it going?    m/s

  Two open organ pipes, sounding together, p yt* u3bqq4ga1roduce a beat frequency of 11 Hz. The shorter one is 2.40 m long. How long is the othq 34guy *qt1aber?    m

Two loudspeakers are at iiuoj (6 b(je(9 n4fvcopposite 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 fcb (4ij9i6 voe(u fj(nront 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 m jfb)43olbw. 0.32 m/s what beat frequency would you expect if 5.50-MHz ultrasound waves were directed along the flbw3obf).4 mj low 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/i c0pv5rhe8 1e8 ml:ghs while the moth 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 reflects off the mothm p lehh0 5eg8:1ri8vc?    kHz

  A bat emits a series of high frequency sound pulses as it approaches a mothh,s7 xwcg,- zk. The pulses are approximately 70.0 ms apart, and each is about 3.0 ms long. How far away can the moth be detectex,kgcs -, 7hwzd 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 c8a*9t+7 oy hosr* ndsto send signals from one Alpine village to another. Since lower frequency sounds are less susceptible to intensity loss, long horns were used to n*oc8t 9+ 7syh*rasodcreate deep sounds. When played as a musical instrument, the alpenhorn must be blown in such a way that only one of the overtones is resonating. The most popular alpenhorn is about 3.4 m long, and it is called the F sharp (or G flat) horn. What is the fundamental frequency of this horn, and which overtone is close to F sharp? (See Table 12–3.) Model as an open tube.

  Room acoustics for stereo listening can be compromised by the prev7z gef./e qagww((.h sence of standing waves, which can cause acoustic “dead spots” at the locations of the pressure nodes. Consider a l7a/. ef( qgwzvhg w.e(iving room 5.0 m long, 4.0 m wide, and 2.8 m high. Calculate the fundamental frequencies for the standing waves in this room.
Length : f =   Hz
Width : f =   Hz
Height : f =   Hz

  A dramatic demonstration, called “singing rods,” involves ac3njrgk13(n dqxn/t ; long, slender aluminum rod held in the hand near the rod’s midpoint. The rod is stroked with the other hand. With a little practice, the rod can be made to “sing,” or e t3x1q dnkc(3r n/;gjnmit 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 frequency of axjhh+37qji6 v boui 6vx3q7hj +hjt 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 jz7(jgd+ kl82d bv b9 bt+gl2qon the ground hears the sonic boom 1.5 min after the plane pa tqg lzd 2db(jkbb7vj g29+8+lsses directly overhead. What is the plane’s altitude?    $ \times10^{4 }$ m

  The wake of a speedboat is 15 7 t*o,f1a9mhcd y uxg.$^{\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