chapter 5b - 'imo the third—order Euler equflliun...

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Unformatted text preview: 'imo the third—order Euler equflliun quickly yields the dCSiI-cd SECTION 5.4 mechanical Vibrations in this section we discuss fourtypes of u .m. underdajnped critically damped, and uvéfifl - V -' 3 -. Inmiunn l- rsl ‘11: msformed constant-coefficient equation then 115 1 cases — .in which actual oscillations cc'wj age-- a mm the corresponding general solution with v = In x -'i(|)l_|;. Mimi” HUM-1.11 ' ,‘m {:1 II- i. Frequency: (1),, = ‘lklm = 1544?: “6 Period: P = brim“ = 23/2: "’3“. Frequency (00 =Jm =Jm=8 r'iiii Period: P=2fiitfln =2ms= rrM see 0; rl+6r+25=0; r=-3i4i . ‘ ._ . . The spring constant is l: = ISNIMOm " gnawing-mi" ~ v)+czsin(4v)] = I'3[c.c05(4lnx)+czsin(4lnx1] with 1(0): 0 and :40) = —10 15er mam-11:1”Imam - frequency is (00- — m: m =-_5 rail: .1» .3236 see. {fieoenierofmeeaMis g a 5111/3? ) frequency w nfa pendulum is given. . .,-_ 25d!” : ZER-JL/GM. day (36400 sec) at Paris, then jls fioniltflkfls 24hr2mjn405ec = ; . [e i5 [)2 = 86560”! SEQ NOW [is and R2 its "radius" at the equalOL = 3,132 of Prob'mfi (“"91 Ll. = L2) yields .pfisfic) calculation gives 7.33 ml as the thickness mm 5 (3950+x)1i100 yields x = |_9795 mi E a correct clock with unknown pendulurn .—. 35400 sec, so npl = 86400. The given “Jpn-ind p2 loses 10 min = 600 sec par day, so u Milli omeblem 5 yields But the that that the bun” wiiiiti‘ i these two results yields a- a 0317'. (c) The solution of this equation with rtOj' a when: ox. = ngR. Hence, with g = 32.2 film [hat the period of the particle's simple hmonio-‘rifo'fit'fiii' - p = 2m, = when; w 5063.10, ' 13. (a) The characteristic equation 101v1 + 9:- +2 = (5‘ mm. ,— = — 2 f 5, #112. When we impose the initial oondiiio‘ifis ., A general solution x(:) = o‘e'm’ +c1te'”1 we get Lhéfiiiifi .{ x“) = 50(e72115‘e—rn) (h) The derivative m) = 252"".4'20‘; _ when r = 10 mm.) as 2.23144. Henna“ ' 14. . 1: == i252"” and 91:3). 2)r3+3"+4=0 has roots r=_2 _ (I - 4. 9):; ;’{O)=0 on the general solutirm -2.r -4[ ‘ _ Irmlntion :0) = 4: - 29 that dcbcfibes {2)r2+4 =0 has roots r=1—2l-‘/i gqtuti n U 101:2. x10) = D on the general 501ution E 17' -.ser|]iep1rli6fllar solution um = 2.10505” . sham: in the following figure. with damping The characteristic When we impose the initial conditions .1: t hll WW I on = (c. + c106“ we get the minim; ‘- ""“"““-1--rI-m- ‘I- ' critically damped motion. I . without damping The characteristic aquatic we impose the initial conditions Jaw] = 5. :16 W) = A cos(4r) + B sin(4r) we get the pmicmarlm -_v “(0 = 5eos(4 r) +%sin(41) a Icharactcristic equation 3r! + 30r +63 = 0 has roots r = e 3‘ _ "I. toitialoonditiuns 1(0): 2, ITO) = 2 on the general solution 'gel-tltc'particular SOIUUOI'I I“) = 48—3" - 28"“ that describes characteristic equation 3r2 +63 = 0 has roots r : t tJ2_1. "conditions xfll) 2. x'(D) 2 on the general solution —5 -ll_} wcgct the particular solution 18. With damping The characteristic aquatic ‘25:" IE!) u Ema?“ _ 02149) ‘ When we impose the initial conditions :10 I x0) = 24' (AcosdH Bsin4r) weget the I inthe figure at the top of the next page. 5 x0) = ‘ 2 8—]. sin 4: = 2!“ mfiifil- - , .+169=0 hasroots r=-5!2i6i. When We =4. x’(0)=]6 on the general solution chmtnristic equation 41-2 +169 = 0 has roots r = 1r 13:72. conditions 1(0) =4, {(0) = 16 on the general solution , 13:! 2)“ get the particular solution ' E] s i 233cos[£!—O.55}7 . l3 2 21. With dampin 7 When we impose ' x(1)= 8"" (donut-+1 that describes nuclei-damped ml -' a Without damping The Chandra-Ii]; When we impose the initial Common "(1) = A cos(2J§ t) + Bsinu‘fgilweoe; that describes underdamped motion. Without damping The charactalistic equatiififi -3 [Mi], and k = 24 lblfl, the differential o The charaCEeristic equation When we impose the initial Corlditions .4. (Acos41J5 + Bsin4rfi} We get .-+1921'= 414E- ' ablation If!)=8 *1oos4:J§+(t/J§)sin4r‘/§] {Wt/5):" [(Jirzxos4rJ5+(1r2)sin4iJ§] “1215)! east4iJ§ #2116). ..‘tudeis 2N5 = 1.15 ft; the frequency is 4J5 z 6.93 ' __-:s :16. weget w- '- JHIOD. But we are given that '(80 cwleslmin)(21!)(l minIGO sec) = 32:13, \elds l: 5 701311113. ;).",sec Equation (2!) in the text yields c = 372.31 - l..86l5 Finally 9 "p’ = 0.0] gives I: 247 sec. 7 35in all]. 33in air] +e"’[—Aaisin mt + Braces am}. meequatiuns A = x0 and _..____ 8mk Ham—17:7— 3; If m) = Ce'F'costmu- a) then x'(l) = -pCe""cos(aJ.t— 0:) +00sz 1 yields tanwlf- a) = -p!w.. 33. If in = inl and x2 = 102) aretwo successive local so = Cum—Phi 905mm ' all X: = Cexpt-ptz) coswm— a) = agg- HCRCB x1! X2 = erpl-pth '12)]. and therefore ln(x1!x2) = -p(tl '12) = 2191' 34. With n = 0.34 and r2 = 1.17 we firstusethe ‘_ Problem 32 to calculate a): = 27d(0.83) as 7.57 _ x; = 1.46, the result of Problem 33 yields p = (110.83)1n(6.73ll.4 ’ Then Equation (16) in this section gives = 2mg = 2(100 and finally Equation (21) yields mwwww ”41'0“ whenwe 'fié x'(l)=0 on the general solution 311m m[(—1-10")r] )p,+(—l-10")c, = 1 2* '5'. This gives the pmficular solution wwyaxpl-m'”) =10"e"sinh(10'".')_ on rz+2,+(l+]o4“)=0 has roots r :—l:t10'"i. When We - "ans x(0)= o, X'(1)= 0 on the general solution g"[Aoas[ID‘"r)+Bsin(10‘"r)] '_ Hg]: 0, —cE+10"'c1 = l with solution r:l : 0‘ c2 : [m This " mlnlian 3:30) = lfl'e"sin(10"'t). I 4. (10"!) = le"-lim—————smh(m_ 0 = re" and m 10'": 1 . mm” = ”shaman-"n _ M, 5- m Hr": ‘ .mm = liflfiiuhayfl = o (by L‘Hfipital's rule. for sgcnou 5.5 ”ONHOMOGENEOUQCl THE METHOD OF UND " always successful — in which case the me complementary function is known. Howey". linden: well with a summing!!! large number of the nonhomugefi r: if“ "'3‘!” arise in elementary screntific applications. ' ' Ill 1 ‘31 I. In cach 0f l’mblems 1720 we give first the form of the trial 56 the coefficmnts we get when we substitute yum into the/dig? terms. and finally the resulting particular solution y“. . L ymd = A9“; 25A : 1-, yp = {”25”}: 2. J'ma, = A+Bx; —2A—B=4, ~23=3; y” = {flag}! . 3, yum, = Acos3x+Bsin3x; -lSA-—3B=0, 3,]-1'5-3' ya = (cos 3:: - 5 sin 3x)f39 5, First we substitute sinzx = (l — ms 2x)l'2 on the right l'i’ah equation. Then: I ‘ {J t 3m] -, A+Bc032x+Csin2Jq 14:1]2, —3B+‘2C="I ' ' yp = (13+ 3c052x— 25in2x)126 6- Jim, : A+Bx+Cx2; 7A+4B+4C =0, 73+ yp = (4 - 563: + 49x2)i343 7. First we substitute sinhx = (e’ - 9")”. 0111119; equation. Then: I ytrial = Ae‘uBe“; I fimcn'on - {war it - (”firsinhzr “J: I amnion J" = e", +33” - Then: EB 2, _6,1=J; y, = {lrsin 3x- 33:035..”6 'Ihc mmpiflflmm fimction I I its-uh: y, = (3: —2x}/s 0. 24B=l; y, = (—3x2e‘+x3e‘)/24 item. We cannot solve the characteristic equation «My function, but we can see that it contains no solution yakI = A leads immediately to the 17- First we note the dnptt ‘ Then: y“ = x[(A+Bx)cosx+(Cq-I‘J£ji .\ 23+2c=o 4b=i,-2A+2n.1, In 3 (xlsinx-xcosxlld 18- First we note the duplication with the comp ye = cle” + (38' +c,e“' +c.e". Then: yimi = XML") + :03 + Car) e"; —6.4 = 1. 12'3" ,.p -_-- 424“! ~ 19m“ + rule‘wm ‘-' 19_ First wc note the duplication with the pm ”i .+ ”a” . 1. (which corresponds to the factor 1'2 ol'lhe characr : )‘uial : x2(/l + Bx + 062); 4A-t- lZB =—l, 1'23 yp = (mg: — 4x] +x‘)f3 _' mu. _‘ 10. First we note that thc characteristic polynomial r5? . to the duplicating part 9‘ of the complementary. . ytrill. : A+x(Be‘); “A=7, 33:1; ypi ln Problems 21430 we list first the complementary function a function yi. and finally the actual trial function yII inwln complementary function has been eliminated. ll 2]. y: e‘(c,cosx+clsinx); yI : e‘(Acnsx+Bsinx] yp = x‘e‘ (Acosx + Bsinx) it = (A+Bx+Cx1)+(De’) -. yp = x3-(A+Bx+sz)+x-(De‘l‘) 22. V = (c,+c1x+cixz)+(c4e‘)+(c,e" ;, 23. y: = c.cosx+czsinx; yi = (A+Bx)cos2x+(c+D;).".‘ y,, = x- (A+Bx)cos2x+(C 33. (15 mh‘f 8, Sin 2x) ”c0052: 1- 95in 2 I) ”on; + (“052’ + D 51" 2"] 34. 35. 36. complementary function ya, the trial solution y" for the and tho corresponding general solutiOn yg : yc + yp where outs an n, .so as to satisfy the given nonhomogeneous 11m equations obtained by imposing the given initial ' 81' solution y(x). 37. Ci :1, 3c2+215 = 0 y(I) = (lScos3x—25in3x+33in'2:c). .1": = clcosx+czsinx; y" = x.“ y“ : alcosx+czsinx+éxsinx cl = 1, 6‘2 = *1; y(x) = cosx-sini- y: = e‘(clcosx+czsinx); y“ = y“ = e'(c.cosx+clsinx)+l+xi2' c1+1= 3, cl+c2+112 = 0 y[.\‘) = e'(4cosx—Ssinx)I2+l+xIZ_ Y: : cl+czx+cleat+cteh§ yu- h 3" yg = cl+czx+c,e‘1‘+c¢e“— ”15-; cl +cl+c4 31' 62-263+2c‘=1_, ¢ 320:) = (234 +240x—9e‘2‘533e‘f x I- y: = C|+Cze +0111 ’ y a? .1 ya = CI +1239" +caxle. Solution of this system gitres final particular solution of Problem-'41? . 41 (a) cos3x+isin3x = cos’ x - 3(cos x) (l — cos: x.) _ 0 ~c +c _C =0 1 and readily solve for cns’x = icosxp ’ ' I ‘ i similarly by equating imaginary pans? ' Se‘HOcosx-Zflyd ‘ J'; .-= A+Bx+sz+Dx’+Ex‘+Fx5 leads to the equations A~B-2C-6.D+24E = 0 _BI-2C-6D-24E+120F = 0 . , 313-123—601? = o 2. 44. We use the identity sinxsinsx = in 45—20:? _ solution yp = Acost+Bsin-2x+_ I y" +y'+y = Jicoslx—é-costl‘xl W D = 2/141. The resulting general 45. We substitute sin‘x = - .'_II"I_IHn-:u».h ‘ 4 Wgfindthflt A =—mo, 3:0,- so when We (llsficos 4x. substitute-in yp I III-Email: - pin 43 the differential equation can be Min-Bl} as $709331. Using the identities 1 {H1 0 we subsmute the trial SOlUtion the integrals and find that - in: = cimx+czsmx' s ‘mx+(c+m)sinx]+[(E4-FI)COS3X + (G + Hx)5in3x]_ i y!) = (4x 903112;: _ $11114: C=O.D=3116,E=0.F="“32'G=3"23sH=0-Hence 1 byy=ye+yl+y2 where . +‘3?sinx)fl5 and y2 -_— {3 sin 3x- 4x cos 3x)/128_ u, = (cosSx—Scosx)l20, "I =( _ .mdepmdent solutions yI and y2 of the associated hOmogeneous #370?» h). the coefficient functions ' Pa = —(U4)(c.os 1‘ “’5 x ‘ 5i“ 2.1: 5h”) + (1' = —(1I5)cos 3x (I) yltxmx) dx Wm ‘ (1)15 and uz(x) =I WI?) 52, y. = cos 3x, y; = sinSx, "i = —(6x—sin6x)136,l u, = = "IJ’|+"2J’2 aqu. (32) in the text, and finally yp itself. _ J’P -—- —(.t cos 320/6 .3” = e", W = e"3r ‘ ' - 53. y. = cos 3):, y; = sin 3):, u; = -(2{3)tan 31:, u; = 2:3!" yI1 : (2!9)[3x sin 3:: + (cos 3:) lnlcog3 . 54. y] = cos x, yz '-' sinx, H; = ucscx, 11;: cosxcsczk yp = —] — (coax) lnlcscx—cmgl _ 't 55. yl = cos 2):, 3n = 5m u; = -(1!2)sin2xsin2x = ...
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