Nối tiếp nội dung phần 1 tài liệu Phương pháp giải bài tập trắc nghiệm cơ học 12, phần 2 cung cấp cho người đọc phương pháp giải bài tập trắc nghiệm sóng cơ và sóng âm. Mời các bạn cùng tham khảo nội dung chi tiết.
Cty TIMHH MTV DVVH Khang Vigt PtiLiOng ph^p giai bai tgp tr^c nghigm Co hqc 12 - Trgn Trgng Hang BAI TAP C d BAN dy T r e n mat nu-dc dang c6 song, ta thay khoang each giiJa hai gdn song lien tiep la 10cm va chiec la nho tren mat nuTdc nho l e n lien tiep Ian D a n g C H U K I - T A N S O S P G - thdi gian 5s Toe truyen song tren mat nu-dc la: Chu k i T cua song la chu k i dao dong cua mot phan tuf cua m o i trUdng c6 song truyen qua B V = 6cm/s \ \ 4cm/s •'•r•;^'•^•^r^''''r - Tan so cua song: f = C v = 8cm/s D v = 2cm/s Giai > • ' Khoang each each giffa hai gdn song lien tiep la bude song: X = 10cm La nho nho l e n lien tiep Ian iJng vdi chu k i dao dong, vay 2T = Vi du: M o t ngiTdi quan sat tha'y chiec phao tren mat niidc bien nho l e n cao 10 Ian 36s Chu k i cua song bien la: - A T = 3,6s B T = 4,0s ' - > T = ^ = 2,5 (s) C T = 2,0s I,.' I.•••• • ^ • i ' D T = 1,5s Toe truyen song: v = — = ^ = 4,0 (em/s) T 2,5 Giai !]:hpn dap an A Nu^dc bien tai phao dao dong c6 song truyen qua nen phao dao dong Dang VIET theo Phao nho len cao 10 Ian tufc nu-dc bien tai diem dao dong dat ciTc dai - Uf^^ =: Acoso) t - - = A c o s 0)t - - ^ Chon dap an IJ BU6c s6riG T A I M O T D I E M Phu-dng trinh song tai M each O khoang O M = x song truyen tiT O tdi la: f = (s): cung la chu k i cua song bien Dang TRIPOl B i e t phu^dng trinh song tai O la: Uo = Aeoscot 10 Ian Thdi gian giiJa 10 Ian ciTc dai lien tiep la chu k i (9T) V a y : 9T = 36 => T = P H U O N G £-i x) Phu-dng trinh song tai N tru'de O vdi O N = x (sdng truyen tijr N tdi O) la: S6NG N_v_ u ^ = A c o s cot + ; : X - Bu'dc song X la quang diTcJng ma song truyen di diTdc mot chu k i - Cong thufc: A = v.T = y , vdi v la van toe truyen song - Hai phan ttf tren cting phUdng truyen song cac m o t biTdc song X thi ^ O Vi du M o t sdi day O A rS't dai cang ngang Cho dau O dao dong theo phU'dng vuong goc vdi day PhiTdng trinh dao dong tai O la: U Q = 2eos 57Ct + - - (em) dong pha Biet toe truyen song tren day la 2m/s Hai dinh song lien tiep each mot bi/dc song X i • • — • ' Phu-dng trinh song tai M each dau O khoang 50cm l a : Vi du 1, M o t day dan hoi cang ngang Cho mot dau day dao dong theo phu'dng thang du-ng vdi chu k i 2s thi tren day c6 song truyen d i Sau thdi gian 0,3s dao A u ^ = cos 57rt + dong truyen di du^dc 1,5m Bu-dc song l a : ' ' A.X = 2,5m —- • B.X=\ • C = 5,0m D.X = 4,0m C u ^ = cos 57tt - (cm) B U w = - c o s j i t (cm) 7t - (cm) D u^^ = cos 57tt+ — (cm) Giai Giai Toe truyen song: v = — = - ^ = 5(m/s) At 0,3 Birdc song: X^v.T - 6J Cd: U Q= 2COS 57tt + M - 4J = 5.2 = 10 (m) Nen: Chon dap an B UM = cos 57t t - - + — = 2eos 57t t- 05^ J + — = 2cos(57it - 7t) = - 2cos57tt (cm) 1Q4 ••••• 195 Chon dap an B Phu'dng irinh dao dpng truyen den M : V i du Song truyen tren phUdng x'x tiY M N each 40cm vdi hiidc son X = 0,8m Bie't phUdng trinh song tai N la u ^ = 4eos SOTTt (em) Phu-dng = 2cos47r t - 0,3^ = 2cos 47rt 4J (em) Chpn dap an D Yi du M o t song cd hpe du'de truyen theo phu'dng Ox vdi toe dp 20em/s Cho trinh song tai M la: A U M = 2cos4Tr t - • rang truyen di bien dp song khong doi Biet phu'dng song tai O la 371 = cos 50711 (cm) (em) B U M = e o s 507tt ) (cm) D U M = e o s 507:t - C U M = 4cos507tt (cm) "o = c o s (em) l i dp dao dpng tai M each O 40cm liic l i dp dao dpng tai O dat cifc dai la: A Giai -t v6 y UM = B 4em UM = :, • C UM = -2em D UM = 2cm Giai N —1— • UN = cos 507rt - - =4 UM COS -t UQ = 4C0S 27tx V6 ^ 507rt - - + X { U M =4eos- (dau + V I song truyen den M trUdc) 7C 2Tt.0,4 U M = e o s 507ct - - + — '•*f ( 371^ = 4cos 507it + — 0,8 I J (cm) • UQ: Chpn dap an A / 0,4 x = 4cos — t t - 0,2 = 4cos (cm) ^71 ^ n max cos - t = ^ - t = k27t v6 y V a y : U M = c o s k r - — = cos 7t = (cm) - V i d u Sdi day dan hoi Ox ra't dai Qang ggang Cho dau O dao dong dieu hoa theo ph^dng thang duTng vdi bien dp 2cm, chu k i 0,5s L a y t = la liic dau Chpn dap an D dat l i dp cifc dai Toe dp truyen song tren day la 8m/s Phu'dng trinh song tai Dang M each O 50cm la: T I M B U C SOIMG X V A V A N T O C V B U M = 2cos 47tt + — A U M = 2cos4TCt ( c m ) C UM = cos B I E T F H U O M G T R I N H SOING 47Ct (cm) D U M =2COS 47tt- 7t So sanh phu'dng trinh da cho vdi phu'dng trinh tdng quat: (cm) 27tX^ u = Acos cot - • ) bu'dc song X X (em) • Giai • Phu'dng trinh dao dpng tai dau O: U Q = Aeos(cot + cp) Vdi: + 271 271 T 0,5 (0 = • + A + t = 0, u = A A = Acoscp = 471 (rad/s) (cm) coscp = ->(p = V a y : u,, = 2eos(47it) (cm) 196 I T i m van toe v: T i m X:=^v - — T hoac so sanh phu'dng trinh da cho vdi phu'dng trinh tong quat: u = Acos CO t - - => van toe v V r TtX ^> d u M o t song ngang truyen tren day eo phu'dng trinh u = 2cos lOOTTt-(cm) x tinh bang cm, t bang giay Bu'dc song la: A A,= lOcm B.X = 5cm C.X = 20cm D A, = 40cm 197 Phuang phdp gii'i b^i t$p tr^c nghigm Cp, hgc 12 - Tian !i:in(j Hifng Dang TIM V A N T O C D A O D O N G C U A M O T D I E M Giai PhLTcfng t r i n h d a c h o : u = 2cos lOOnt- TREN FHUONG TRUYEN 7TX To X cijng ddn vj '• T a diTdc: — = — ^X 10 X i > ^ J t r o n g d o x va , du u = — = -coAsm cot-X dt » V i d u PhU'dng t r i n h s o n g t a i d i e m M v d i O M - x l a : ' " ' v:: Vi d u PhiTdng t r i n h s o n g t a i m o t d i e m c t o a d p x t r e n phU'dng t r u y e n soim v a o i u c t diTdc c h o b d i : u = c o s ( t - , x ) ( c m ) t r o n g d o t t i n h b a n g giay, b a n g c m V a n toe t r u y e n s o n g l a : , | A V = 4m/s B V = 2m/s , I'feP: : C v = 5m/s ( c m ) t r o n g d o t t i n h b h n g g i a y , x t i n h b h n g c m V a n tdc d a o d p n g t a i d i e m M c x = 10cm l u c t = I s l a : A ,; ' B - , m/s u = — = -37isin dt 1: S o s a n h v d i phU'dng t r i n h s o n g t d n g q u a t : V d i t = Is, ta du'dc X = c m , ta c : 20 + 10 0,05 = ~ - ^ l =^ 0,05 = -37rsin - - = 40n ( c m ) Dang (cm/s) = (m/s) g ^ 0,05 ^ 2: V i e t l a i phU'dng t r i n h s o n g d a c h o : u = 5cos t 20 So s a n h v d i phU'dng t r i n h s o n g t d n g q u d t : u = A c o s Tad.«c:M5a^v =^ VI x CO = 400 0,05 d d n v i la c m n e n v c d d n vj l a cm/s V a y : v = 0 (cm/s) = (m/s) ChpndapanA = - , (cm/s) cot-271-!- X ( o ^2 ; U = Acos c o t - ^ XT - X D p l e c h p h a giffa h a i d i e m : Acp = T C ^ ^ — — ; Acp = t — X X t - - T R U Y E N S61NG PhU'dng t r i n h s o n g t a i d i e m c tpa d p X | v a X c u n g l u c t l a : Ui = Acos V DO L E C H P H A G I O A H A I D I E M TREIN P H U O N G 20 = -37rsin- C h p n d a p a n li V a n t d c t r u y e n s o n g : V = — - "^^"^^^"^^ = 0 Cdcli D m/s -t-0,2KX u' = -37:sin - - , (0 C 9,42 m/s V a n tdc dao d p n g l a dao h a m cua li dp u theo t: PhU'dng t r i n h s o n g da c h o : u = c o s ( t - , x ) 27rx u = A c o s (Ot - • u = 6cos - t - , i x D v = 400m/s Giai Cdcit X V a n t d c c u a m o t d i e m c t o a d p x l a d a o h a m c u a u do'i v d i t: = 20.Vi\h b h n g c m n e n A = ( c m ) ChondapanC X 27rx^ ^ , r PhU'dng t r i n h t r u y e n s o n g : u = A c o s cot So s a n h v d i p h i f d n g t r i n h s o n g t d n g q u a t : i i = A c o s cot - S6NQ X Vf d u S o n g t r u y e n t r e n d a y d a i v h a n v d i b i f d c s o n g X K h o a n g e a c h giiJa hai d i e m t r e n day dao d p n g c u n g pha each A d = 2kA B d = ( k + l ) ? C d = k - D d = k?^ (vdi k = 1,2,3, ) e Giai H a i d i e m tren day each k h o a n g d dao d p n g c u n g pha k h i : Phuohg phap giai bai t^p trSc nghigm Co^bpc 12 - Trai Acp = 2n.— X = 2kn HKng (vd\k= d = kX Cty TNHH MTV DVVH Khang'Vift y,' du Hai diem M , N each 28cm tren day c6 song truyen qua luon luon 1,2,3, ) lech pha vdi mot goe Acp =(2k + l ) ^ vdi k = 0; ±1; ±2; Chon dap an D Vi du Song truyen tren day dai v6 han c6 bu'dc song X Mai diem tren day dac dong ngu'dc pha each A d = k Ichoang ttr 22Hz de'n 26Hz Tan so cua song la B d = U C d = U D d = k + V ( V d i k = 0, 1,2, .) ;, 2y X Hai diem tren day each khoang d dao dong ngUdc pha khi: ' X d= Chon dap an D f ^ k+i I X vdi k = 0, 1,2, 2j Hai diem tren phUdng truyen song dao dong: Cung pha each d = k> lech pha gdc ' each D d = 25,0cm Giai X vdi X- — , 4d Dang 2.3+1 0,28 = 25 (Hz) Chon dap an A BIET L I D O C U A S O N G T A I MOT D I E M NHAT DINH V A O • Rie't li d thdi diem t, la U| Tim li U2C! thdi diem t2 • Neu At = t, - t = T thi T Neu At = jt, - , = Y thi nen Acp - • Ne'u At^T T thi giai he f 27td.f V f =I _ d=^ = = 0,625 (m) = 62,5 (cm) 4f 4.20 Chon dap an B 200 KHAC U2 = Ui Ji'f! U2 'lit:' I • fvi = -u i'i,! son! Uj = Acos(coti +cp) U2 = Acos co(ti + At) + cp Vi du Tren phu'dng Ox c6 song truyen qua vdi chu ki ciia song la T Vao lue diem Pco l i d o A U2 = 2cm ^, ^ B U2 = -2cin • , C U2 = 3cm 7t V • nao diem P tren phu'dng Ox c6 li Ui = 3cm thi sau liic thdi gian T 27td Hal diem dao dong vuong pha: Acp = — Vay: ^ , B d = 62,5cm C d = 50,0cm -1]^ ,,7t V k + , 2k + l k + f = _ = v = = (*) X 4d 4.0,28 0,28 22sin(ntj - , i x ) = - C chat k h i Bu'dc song la quang di/dng ma song truyen di di/dc mot giay III du B chaft long I :,„:, + u, =3cos(7rt,-0,27tx) = V , J + l i dp dang t i n g tiTc ; D truyen du'dc chaft k h i , long va ran Giai Luc ' 12.4 Co phat bieu nhu'sau ve bu'dc song: • • C U2 = - v ' c m ' Phat bieu dung la: A Ca I , I I va I I I B Chi cd I va I I C Chi cd I I va I I I D Chi cd I I '2.5 D o i v d i mot m o i tru'dng nhat dinh thi to'c dp truyen song A chi phu thupc vao bien dp cua song , •i B khong d o i C chi phu thupc vao tan so cua sdng D phu thupc vao bien dp va tan so cua sdng 203 Phi/Ong phap gi^i bai t j p trSc nghi§m Cc hpc 12 - T d n Trpng Hung Song truyen tur O tren true Ox, toe truyen song la v, bu'dc song X Ne\ bieu thiJe dao dong tai O la: Uo = Acoscot thl phu'dng trinh song truyen theo true Ox la: X A = Acos cot - - C = Acos cot B u ^ = Acos TUX I u = 4cos X 50cm vdi to 4m/s Phu'cJng trinh dao dong cua M la: A U M = 2cos(1007tt-7i)(cm) B U M = 2eosl007it (em) 12.7 Cong thiJc dung la: A ;^ = v.f (cm) t tinh bang giay, x tinh bang em Toe 507rt - — X 10 truyen song tren day la: ' ' - • A V = 5m/s I T B v = 5cm/s C v = lOm/s D v = lOem/s j2 15 Phu'dng trinh dao dong tai mot diem O tren phifdng Ox la U(, = 2coslOOTtt ' (cm) t tinh bang giay, sau dao dong truyen den M tren Ox each O 2nx cot - • D u^^ = A c o s CO j2.14 Phircfng trinh cua mot song ngang truyen tren sdi day dan hoi ra't dai la: B.v = X.T C f = v ^ C V 12.8 Cho mot song cd la song ngang Vao luc t song U M (cm) = cos l O O n t - D khac vdi A, B, C 12.16 Tren sdi day dan hoi ra't dai c6 song hinh sin truyen di Phu'dng tnnh dao C O hinh dang nhu* hinh ve, phan tiir A dao dong tai diem M tren day la: u ^ = 5cos dong vcti van toe v theo hu'dng chi tren hinh ve Song dang truyen ve: A phia ben phai (cm) t tinh bang giay, sau dao dong truyen den N each M met vdi toe 5m/s Phu'dng ' \ B phia ben trai C hu'c^ng cua v trinh dao dong tai N la: D ngu'dc hU'dng cua v A U N = e o s ( T c t - i ) 12.9 Mot ngirdi ngoi d bien nhan thay c6 20 ngon song di qua trU'dc mat minh 76 giay Chu ki cua song la: :;nn (cm) B U N =5COS r t - ^ D U N = (cm) J M , ? , i?'Vv;r;i / i ; C A T = 4s 257:t-^ C.T=15s D T = —s 76 38 12.10 Mot ngUdi ngoi d bien thay khoang each giiJa ba ngon song lien tiep la U N =5eos(257it) (cm) -5 cos 25Kt-^ (cm) B T = 3,8s 12.17 Tren day dan hoi kha dai eo song truyen qua Song truyen theo ehieu tif • M -> N nhu' hinh ve vdi toe Im/s Biet phiTdng trinh dao dong cua diem N 15m va ngu'di de'm du'pc 10 ngon song di qua trUde mat mlnh th5i la: Ufq = 4eos gian 27s Toe truyen song bien la: A V = 2,5m/s B V = 2,78m/s C v = 0,4m/s D v = 0,28m/s 12.11 Mot ngu'di go mot nhat bua tren du'dng sat va each day 1530m c6 mot ngufdi khac ap tai len du'dng sat thi nghe du'dc hai tie'ng biia each 4,2s Biet toe truyen am khong la 340m/s va nho hdn toe truyen am I phu'dng trinh dao dong cua M la: i A U M = 4cos(507tt - n) (em) =4cos m - ^ C sat Toe truyen am sat la: A V = 3600m/s B v = 2700m/s C v = 8400m/s D v = 51 OOm/s 12.12 PhUc^ng trinh song truyen theo true Ox cho bdi: u = 5eos(207it - 0,47tx) (cm) t tinh bhng giay Chu kl cua song la: A T = 0,2s B T = 0,4s (cm), t tinh bang giay M each N 65cm, 507it C T = 0,ls D T = 0,3s C t - - X (em) N ; B U M = 4cos50;ct (em) D U M =4eos 507tt + - (em) 2y 12.18 Day dan hoi Ox kha dai cSng thang nam ngang Cho dau O dao dong dieu hoa theo phu'dng thang diirng vdi chu ki 0,2s va bien 3em Toe truyen dao I dong tren day la 2m/s Lay t = la lue dau O dao dong qua vj tri can bhng theo ehieu du'dng Phu'dng trinh dao dong tai diem M tren day each O m la: 71 12.13 Phu'cfng trinh song tren true Ox la: u = 3cos (cm) _M v_ A U M =3 COS 107:t + (em) B U M = 3cos(107it) (em) C UM = 3cos(107tt + 7t) (cm) X tinh bang met Bi/de song la: A.X^lm B >i = 4m C X = 2em D = 4em D U M =3cos ' l O T T t - ^ ' (em) 2j 205 204 Hhd'dng ph^p giit bit tjp trie nghigm Do hgc 12 - Tran Trgng Hung 12.19 PhiTcfng trinh dao dong cua mot diem M tren phiTdng Ox c6 song truyej, j2 26 PhU'dng tnnh song ngang truyen tren phiTdng Ox nhU' sau: qua cho bdi: U M = 2cos(47it - 0,057tx) (cm), t tinh bang giay va x V\n\y u = Acos bang cm L i dao dong cua diem M c6 toa x = 2cm vao luc t = 0,5s la; A u = 2cm B u = -2cm C u = l c m D u = - l c m ^2n t + ^ STIX • , x tinh bang met Do thi cua li u theo t tai = 10cm la du'dng sin ed dang 12.20 D a u O cua day dan hoi raft dai dao dong theo phiTdng vuong goc vdi d a y , CO phu'dng trinh: U Q = A C O S "• ' : T vao luc t = — C O li 1,5cm B i e n dao dong la: A A = 2cm B A = V c m , , '""f"/T\'" — t D i e m M tren day each dau O —bu'dc sono T A i \ / I \ \ j ^; _ _/4 3_ _T T \ -A •-s •• -A A / T ' V / B A C A = % / c m "\ D A = 2^3 cm u i ,• 12.21 D i e m O tren mat nu'dc dao dong vcti phu'dng trinh: Uo = Acos47it, t O hai d i e m gan nhat tren du'dng thang qua O each A d = l m B d = 2m C d = 0,5m A A tinh bang giay To'c dp truyen song tren mat nu'dc la 2m/s Khoang each giL7a D d = l , m -A T r T \ T \ / ^ A : / Viy T I i \^ -A \ i Z ? - A D 12.22 M o t day dan hoi kha dai cang ngang D d u O cua day dao dong vdi tan so 36Hz thi tren day c6 song ngang truyen di vdi van toe khoang tu" 4m/s \ 12.27 L i i c t = dau O cua day dan hoi rat dai cang ngang dao dpng theo phufdng 5m/s Quan sat tha'y hai d i e m tren day each 40cm dao dong cung pha t h i n g dilng v d i phufdng trinh: U Q =3eos t - ^ Toe truyen song la: A v = 4,8m/s B V = 7,2m/s C v = 4,1 m/s D v = 5,6m/s giay T r e n day ed song truyen di vdi biTde sdng~K= 4cm Dang cua day vao 12.23 M o t day dan hoi ra't dai c6 song ngang truyen qua vdi van toe v = lOm/s, luc t = 1,5s la: t^n so song khoang tiJf 40Hz - > 60Hz Hai d i e m tren day each > * u (cm) (cm) 6,25cm se dao dong lech pha vdi goc Acp = k + - - v d i k = , , , (cm), t tinh bang 3 tan so song la: A.f=20Hz B f=IOOHz C f = 50Hz X (cm) X (cm) D f = H z 12.24 M o t song ngang tren day dan hoi rat dai c6 phU'dng trinh dao dpng tai d i e m ed tpa dp x vao luc t la: u = Acos(47it - a.x), t tinh bang giay, ^ la hang so diTdng Bie't toe dp truyen song tren day la 16m/s Gia trj cua hang so a la: A a = 0,25n(m) ^/:,:r.^i.::^:'ry C a = 0,57t (m) • V B a = 0,257t (1/m) , D a = 0,57t (1/m) v 12.25 M o t song ngang ed phiTdng trinh song la: u = 0,3cos(314t - 5x) (cm), t tinh bhng giay V a n toe dao dpng cifc dai eua mot phan tuT vat chat c6 12.28 PhiTdng trinh sdng tren phiTdng Ox la: u = 3cos(57it + 0,4x) (cm), t song truyen qua la: A v„,ax = 0,3 em/s C v,„ax = 94,2 cm/s B v,„ax = 0,6 ' D v„„x = 15,8 cm/s cm/s tinh bang giay T a i mot diem nhat djnh tren day vao liic nao no cd l i dp 2cm thi sau s d i e m dd cd l i d6: A u = l c m B u = 2cm C u = - e m D u = - I c m 207 Cty TIMHH MTV DVVH Khang Vi^l 12.29 Hinh ve ben bieu dien hlnh dang scfi day chieu truyen song dan hoi thcJi diem t c6 song truyen qua theo chieu tij" trai qua phai diem Dap an A , ,^ r , Trong 76 giay trifc^c mat mlnh c6 20 ngon song di qua tiJc cho c6 20 Ian ni/dc len cao nhat Thdi gian giffa 20 ian lien tiep la 19 chu ki Vay: P d vj tri can bang va Q d vj tri cao nhat 19.T = 76 = > T - — = (s) 19 Hu'dng chuyen dong cua P va Q thcJi diem t la: - • f.- 12.10 Dap an A A Pdi len, Q d i xuo'ng B P di len, Q diJng yen C P di xuong, Q di xuong D P di xuong, Q diJng yen HI/6NG DAN • H") Khoang each giifa ba ngon song lien tiep la h—^ ^ < 2:^ (Hinh ve) nen: X = — = l,5 (m) \ ^ \ GIAI • 12.1 Dap an C C Sai vl: song ngang la song cac phan tuf cua moi tru'dng dao dony theo phu'dng vuong goc vdi phu"clng truyen song 12.2 Dap an D Song doc truyen du'pc ca chat ran, long va 12.3 Dap an A Song ngang truyen du'dc cha't ran (va tren mat niTdc) 12.4 Dap an D Chii y rang phat bieu III dung la: 10 ngon st5ng lien tiep di qua trifdc mat muih ti'rc C\\Q vat chat da thifc 27 hien dao d()ng lien tiep nen chu ki song: T = — \5 Toe truyen song: ^ = — = (s) = 2,5 (m/s) 12.11 Dap an D Ngirdi nghe se nghe hai tieng bila: tieng am truyen du'dng sa't (nghc Bu"dc song la khoang each giiJa hai diem GAN NHAU NHAT tren phu'dng truyen song ma dao dong tai hai diem dong pha trUde) va tieng am truyen khong Goi V va t la toe va thdi gian truyen am du'dng sat, ta ed: 12.5 Dap an l i Doi vdi mot moi tru'dng nhat djnh thi toe truyen song khong ddi 12.6 Dap an C ^ x^ u^^Acosco A c o s CO t - - = A COS cot U M = Aeos cot CO 271 2K vdi — = — = • nen V v.t X S = v t - ( t + 4,2)= 1530-^t = - ^ - , - , ( s ) 340 Vav= ^ Tlx t D c6 ;i = v.T = - hay: T = - f 12.8 Dap an B , : Phu'dng trlnh song eo dang long quat: u = Acos cot 27rx V - So vdi phu'dng trlnh da cho: u = 5cos(20jit - 0,47ix) Ta dirdc: co = 207i (rad/s) T =^ CO Vao luc t diem A di len theo hu'dng v nen cac diem cung pha C, E, cung i-'' ?; len va liic t + — cac diem len cao nhat NgUde lai liic t cac diem B, 1^' T dao dong ngu'dc pha vdi A nen di xuong va luc t + — chi'mg xuong thfip ' T , nhat Vay luc t + — song la du'dng cong khong lien tuc nhu' tren hinh ve Q^''^ ket qua ta thay song truyen ve ben trai 208 -^^-^ = ^ 0 (m/s) 0,3 12.12 Dap an C 12.7 Dap an ^ = - ^ = o,I(s) 20n '2.13 Dap an B ^ S So c phu'dng trlnh da cho vdi phu'dng trlnh tdng quat: u = Acos cot -271 — K , i ''J'*,';/ , i : f Ta ladirdc: — = — — -> A = (m) '2.14 Dap an A So phu'dng trlnh da cho vdi phirdng trlnh tdng quat: u = A cos 2n 2nx) Phuong oiy ii\]HH M i v u v v H T ' T i a n g v i e i ph^p giai bai tjp trie nghigm Co hpc 12 - TrSn Trpng Hung T a diTdc: — T = 507i T = — = , (s) 50 + X, = ( c m ) + A = 3cm + t = : Uo = va X 10 — = 107t (rad/s) 0,2 1" cm Toe t r u y e n song: v = — = CO = — = T • / •i > U Q coscp = 0 = Acoscp = 0 (cm/s) = (m/s) • U(, = - C L ) A s i n ( p > [sm(pn = 0,5 ( s ) ; ? i = v T = 2.0,5 = ( m ) ^^«''',' 471 e a c h n h a u - J = 0,5 ( m ) * 12.22 D a p a n A gian At = — V a y : V '' ' ' > ' 14,4 , , , H a i d i e m dao d o n g c i j n g pha each nhau: u^^ = cos 5071 t + = cos - 507t t - 0,65 ^ r V - Uo - Acos((Ot + cp) X,- 1 -1 o f , ,u O d.f 0,4.36 k k d = k ? i = k - v d i k = 1, 2, 3, => v = -— = — = 4cos(507it + 327t) = 4cos507tt ( c m ) Vdi: X 1,5 ( c m ) n e n = H a i d i e m g a n n h a u nha't t r e n phiTdng t r u y e n s o n g va d a o d o n g ngu'dc p h a V i s o n g t r u y e n t d i M triTdc n e n d a o d o n g t a i M s d m h d n d a o d o n g t a i N tht'i • 271.X/6 A |2.21.DapanC 12.17 D a p a n B 12.18 D a p a n A r27i T U M < V M = < :cfeMVii}|j>'fi(i!iv iVw I'fAil^-anii' 2n Co: T = — - 0,4 (s) nen At = Is = 2,5T: d i e m qua li - c m 571 12.29 Dap an D 8(m) 12.25 Dap an C I , lai dang cua day la hinh A , ^ , , ^ , 12.28 Daj^ an C 4, , Tom X = 471->T = - - , ( S ) T x „ „ x = - l , = ( c m ) = 1,5?> 2n So vdi phiTdng tnnh da cho thi: • 2KX truyen di xa nhal la: x,„„ = v.t = —.t vdi T = ^ = ^ _ \ n^,, r (0 271 tinoi i.;::;.: In PhiTdng tnnh song tai mot d i e m tren day c6 dang: u = A c o s — t T I': X 7t Chu y rang liic t = dau O bat dau dao dong nen de'n liic t = 1,5s song = 50 (Hz) 2) = 3cos Dang cua day la thi cua u theo x: la du'dng sin lap lai sau X = 4cm • 2.1 Vay: f = 20 2nx^ vOil 40 < 20 k + 2, n Ngay thdi d i e m t: • ' Vy = 0: d i e m Q di?ng yen v j : max nen d i e m P dang chuyen dong Van toe dao dong cua mot phan tuf vat chat c6 song di qua la: u' = — = - , s i n ( t - x ) (cm/s) =-94,2sin(314t - 5x) (cm/s) dt Vl song truyen qua ben phai nen sau — song truyen di difdc — i?ng vdi • du'dng khong lien iiet: P den P' V a y P dang di xuong ( { ' , < '•»> Van toe dao dong ciTc dai: v,„ax = 94,2 (cm/s) 12.26 D a p an D ^ - PhiTdng tnnh dao dong tai d i e m x = 10cm = 0,1m u = Acos • luc t = '2n T u t + 57r.0,l '2n n - Acos — + - IT 2J ' * 13 G I A O T H O A S O N G = Acos—= - *' * ' -' TOMTATLITHUYET Hien tU'dnjj jjiao thoa ciia hai son u = AcosTi = - A K e t qua: tren mat nu'dc xuat hien cac gdn song on dinh CO hinh la cac du'dng hypebol vdi tieu d i e m la «^ Vay thi la hinh D - 12.27.Dapan A ; Phu^dng tnnh dao dong cua song: vdi ?i = cm u = 3cos 2Kt •I , 2i2 X ) Hien tu'dng hai song gap tao nen cac gdn song on dinh goi la hien tu'dng giao thoa cua hai song I Cac gdn song c6 hlnh hypebol goi la cac van giao thoa 213 Phuong phap giai bai tgp triSc n g h i j m Co hpc 12 - T r i n Trgng HLfng Thdi gian ngan nhat de vat di tij' O den x = +2cm Ian thi? hai la: Call 45 M o t van dpng \ i c n tiifcn bang nghe tluiat quay quanh mot true t h i n g diJng vdi toe 90vong/phut \ d i hai tay dang ngang, luc momen quan At= tinh cua ngu'di do'i vdi tru quay la 2kgnr Sau ho dot ngot dat hai tay dp sat than l a m momen quan tinh eon lai K g n r L a y n~ = 10 Dong nang r a u Dap an A fx - Acos(a)t + (p) quay cua van dong vien dat hai tay ap sat than la A.16200J B.4,5J C 36()J T T 5V , , - + —= =- s 12 Co a = - o r Aeos(o)t + (p) D 180J Cau 46 M o t may toe phal tin hicu am eo Ian so 1380!Iz hu'dng ve phia Liic (wt + 9) = "~ thl a = 8m/s" nC-n: - S xa CO tan so 1680Hz Biet toe dp am irong khdng la 340m/s Toe dp to -8 = - ( t ) - A - = B 150km/h C 120km/h (m/s' ) V d i (0 = 27if = 471 (rad/s) ncn: la A lOOkm/h fo' \eos| — \ mot chie'c to dang hifdng ve phia dat may tin may nhan du'dc song phan D 80km/h - > A - ().()5v2 ( m ( - 5N/2 ( c m ) - , V2, Cau 47 M o t banh xe to eo khoi lu'dng 20kg coi nhu" dTa tron ban kinh 20cm Cau Dap an D Dpng nang toan phan cua banh xe to chay vdi to'c dp 72km/h la A 6000J " B 2000J • C 4000J D 3000J W, + W , : - k A - f Cau 48 M o t to dang d giifa ngu'di quan sat \ toa nha cao tang O to dang -A 2\ - - k A - chay ve phia toa nha vdi toe dp 108km/h va keo c o i A m cua coi c6 tan so lOOOHz va to'c dp am khong k h i la 330m/s Ngu'di quan sat da nghc - k x ' - - k A ' - >x ::^± du'dc am phan xa tiV toa nha co tfin so' A 916,7Hz B 1091Hz C 1125,6Hz D llOOHz Cau 49 Rong rpc co hhih dTa tron khoi lu'dng 300g du'dc qua'n bdi mot day khong dan khoi Urdng khong dang ke Dau day co treo vat nang lOOg L a y rOm/s" Tha nhe vat nang thl sau 0,5s vat di duTdc A 0,3125m B 0,5m i> C 1,25m Cau 50 M o t dTa tron quay nhanh dan deu • g = • ^ — ^ X = licMi theo x tang tiTc vat chay ve phia O \ lin .i> the nang - a i '.i - A Vay : t = 0, ,\ •—j= va v > v2 M A , A cos (p cos (p ->\ v - -(oAsifup > sincp < bat dau quay vectd gia toe a' tai d i e m M Iren vanh dTa hdp vdi ban kinh O M 4i ->cp = 3n ?au Dap an D gocabang B - r a d C - r a d HLfdNG D A N D ^ , a d 12 GIAI -4 O +2 m +4 1.-^.0,2(s) 1071 , ,: , • ,v • L u c t = 0: X = 2cos(0) = (cm) • -\ T Thdi gian de vat di li:r x = - » x = - (cm) la At = — + — — 12 Cau l D a p a n C 292 Tai giam ,„,;., quanh tam O Sau thdi gian 2s ke tif li'ic C6T = ^=.2(s) 4i A T a i X = — , lien thco x tang tiVe viit chay dan ve + A xa li'ic the nang D 5m A — rad +A O cung tang tCr nghi vdi gia toe goe — rad/s xung li.il A/ (s) V a As = + I = (cm) 293 _ As Vay: v = — = At 0.2/3 Can Dap an A / - n.— = n.— 2f CauG.DapanC 2^^ Theo de • ^—^ = 0,05% = 0,0005 = 43(CITI/S) 2.'^.600 n = —— = —2 = (bung) -> So nut : n + = ^ : ; , V ^v.400 : < X''"^v-^'~~\X~~X If 21 • , Hoa am bac iJug vdi n = nen: f = ^ l i ^ = 450(Hz) 2.0,3 Cau Dap an D T=^.i^=o,2(s) Co (0 ?, = v.T d,-d, IOTT A.=2A > = 30.0,2 = =2(cm) ^ d,-d, '^f-' ; ^ (cm) 271 n = 2.2 cos — = (cm) ( au Dap an I) - Ne'u X = A.sin((ot + cp) thi a = -(o'Asin((ot + (p) = -2sinlOt (m/s^) 200 V3y : or A = m/s" = 200 cm/s' A = = 2(cm) CO.S (10)^ D o d o : x = 2sin(I0t)(cm) = • Liic t = 0,0785s: x = 2sin( 10.0,0785) - 2sin(0,785 rad) = ^2 (cm) Cau Dap an C a =-arAcos57it i;v'fev' • |a| = (i)^A|cos5;xt| |a|: max |cos5jit| = 57tt = kn - > t = 0,2k (*) CanCan 10 lim D d p: a n A , T, T, T, i 294 ^ = 0,9995-^^ = — g2 0,9995 - ^ = 0,0005 I - - , 0 = 0,025% > 0: chu ki lac du'a ttr 709995 Quang Ngai (T,) vao TPHCM (T.) tang len , r Cau 11 Dap an C / Giffa hai Ian lien tiep hai liic cCing qua vj tii can bang thang diJng va cung chieu CO so' dao dong hdn kern mot ddn vi Vay ne'u N| la so' dao dong ciia lac thiJ nhat (chu ki TO thi so' dao dong lac thu" hai (chu ki T2) la N| - (VI T2 > T| tiJc lac thu" hai chuyen dong cham hdn) Vay: A t - N , T , = ( N , - 1)T2 2,2 [2 N,(T2-T,)=T2-^N, = = 11 (dao dong) T,-T, 2,2-1 Vay: At = N,.T, = ll.2 = 22(s) Cau 12 Dap an D " ' Con la'c d to chuyen dong theo phifdng nhm ngang c6 gia toe hieu dung g' = V g ' + a - = V I O ' + ( N / | T ) ' = ( m / s ' ) "'' ' (*) AT T = 2n Co \ T g T = 2n / |g T Vg' no^^,^ V12 0^ V12 Cau 13 Dap an C Tai dau hd ciia o'ng la biing Song nen: / = m.— = m - ^ -> f = ilil vdi so' bung = so' niit = ULil • 4f 4/ m=5 Vay: f = = 850 (Hz) 4.0,5 Cau 14 Dap an B Con la'c se dao dong vcti bien Idn nhat c6 cong hifSng, liic do: T = T' Vdi: • T la chu ki dao dong cua lac bang - s 295 • T' la c h u kl dao d o n g cua ngoai lUc c i r d n g biJc b a n g Cau 19 Dap an B — V • V i i y : - = — = — ^ v = 15 ( m / s ) V V Cau 15 Dap an D Tan = 54 (kiii/h) L xo va vat in: T = 2K , , , Dp ciJug moi 16 xo sau cat: k| = 2k Do ciJng cua he dao dong: k" = 2k| = 4k so cua dao dong cifdng bi?c bhng tan dao dong rieng ciia ngoai so lire m Chu k i : T ' = 27C cifSng biJc k' Cau 16 Dap an C " Chii y rang: noi dai lifclng x giam di a'r (a > 0) tiTc: X - X I 100 , , T' fk Laptiso: — = , — T Vk' Cau 20 D a p an C Vay tlico de ta can tun: I - cos 2a Dung cong thiJc: sin' a = a co: — = — - 1, vdi : h , =^ - k A ^ ; h , Fi, n, ,,, A, ncn : A , A -, Da c6: A, AI - ' -kAr ' ,2, T >1 = — Ta difrtc: x = 10 — " " " ^ ^ ' ^ " ^ ^ = - 5cos47Tt ( c m ) !,,„j4-.fA Vay : vat dao dong vcti bien 5cm -1 Cau Dap an A I ; A -, - - - ^ - = - , -> - i - = 0,95 A, A, • -v- 0,4^-0,3^ 2gA 2.10.0,05 = 0,07 l a u 24 Dap an B \V(i: / = v T - v — = 10 50K 296 /(, ^au 23 Dap an D \ -„ 7t 27ld, u,^, = cos 50m + -2 I ) ; c ( d , - d , ) 71 , = (cm) - , - n : hai dao dong ngiriJc pha Cau ! Dap an A N c n : Acp = 54-46 Luc vat d vi tri can bang, lo xo dai: /| = /,„;„ + A = 46 + = 50 (cm) Cau 17 Dap an D Vay A9 = _/ — ^ = n = ~ i 'i^sa |-iL:,-i;;:|iyt', M^'ifmrn:!! • t i t v ; ••ji i " • ff>V 297 If Phuong phap g\i'\i tap trie nghigm CO hgc 12 - Iran Trpng Hung Cty TIMHM M ! V O W N Khaiii] Vifil Can 26 Dap an C 2Tid, u , M = A c o s U)t - • \ Co "2M = A C O S ^'t + ^ X J 2TT(d2-d,) A4: = 4:| -4^2 = -K a \ 2TT(d;-di) ' K _ - = 2kix X ^dn-d, (1) LO 1= -UiU X = 490 ( r a d / s ) (2) v P 4TT.I0- = 10(lg " - Ig 8TX) = 10(11 - , ) = 96 (dB) 23 s.S = — X • lit-! • Can 29 Dap an B ' : ni^ , „i 12 Do lech pha cua hai dao dong tai M : Aip = 22 — X ->-2 ' ui/? 2|img 4(img Vao luc to: i W, = - ^ k x ^ = ^ 0 ( , ) ^ c o s ' ( T T t ) = 0,02cos^(10TTt)(J) 300 = Chon true li u hu'dtng len va cho: ^ A, k s r O ( U M ) ' = -Uo(osin((ot„) > - > sin(o)l|,) < 301 "Cty f = Uy cos [ - t o Ngay liic do: 5X] ^ f ii()a;sin [ - t o 5X^ 2TT ^ = U(, J = iio sin(u;to) < cos :au 45 Dap an D Dinh luat bao loan momen dong IiTdng: = —Uo-osin - t ( ) - - J = Uojjcos(u;to) > 40 Dap an - B > ,, =-r «, = 7-90 = 180 (vong/phut) I,CO, = l M j Vi U N < va ( U N ) ' > nen liic diem N d diTdi diTdng AB va dang di len Can ! N ! l i i M T V OVV!) Khang Vigt = 6n (rad/s) '''•'•i A T to = — = — = 0,25 (s) " 12 12 -A y o A 1 • 'Dong nang: Wj ^ - I ^1,(0^=1, w ^ = - (671)^ = 180(J) ' ' Cau 46 Dap an C t=() T Call 41 Dap an B - Thco dinh liiat biio loan momen dong li/dng: O to nhan du'dc am c6 tan so' f vdi: V + V IiCOi - I2CO2 f = f ! R ^-mRf ' ^ x2 - uj, > u), V I R i > R ^ i'.^^v.:iMx/-^l Can 42 Dap an B ' '»^^''>'" r , - ? ; - - - - / ' thu dUdc am c6 tan so f": I', f" = f'.- ] V Co M = I.-t L = I.u; L _ - _ '^•t _ J M ^ • = f • -1 100 , rad 2., TV ^ — - ~ (rad/s ) 10 - R R = I.-t = - m R ^ ' ^ :CU\j = — , * ' I ioj = 6,28.10~^(N) Cau 44 Dap an A = = 3' mg ^' = 1,256 (s) 302 I = i m R ' =-.20.0,2' =0,4(kg.m') v i, CO = - = — = 100 (rad/s) R 0,2 ' : - Dong nang quay: = ^ I c o ' = ^ , 0 ' = 0 (J) V - Dong nang tjnh tien: W, = ^ m v ' =^.20.20' =4000 (J) - Dong nang toan phan cua banh xe: Wd = Wq + W, = 6000 (J) Toa nha thu du-cJc am c6 tan so': f = f — — (v„ la to'c to) V - v„ m/' 271 , :au48 D a p a n D I = - m / ^ d = OG = - nen: mgd (m/s) = 120(km/h) lOy = 27r rad/s Aip = 20TT 0-(2TT)^ • ^ 340-v„ Cau 47 Dap an A vdi 2.10TT - v„ A 2A V = V 340 + V 10" - LOQ = 2^'.A'^p = - - = f.V - V,, Thayso: 1680=1380 Cau43.DapanC ,„ , V + V0 V + V,- - v„ L = M.t = F.2R.l= 10.2.0,5.10= 100(kgm'/s) T la van toe to) Sau to coi nhif nguon phat am, phat song phan xa am va may R Vay toe goc tang dan (Vo V ' 271 V3'g < ^ 10 = 1000 =1100 (Hz) 330-30 303 Phuang p h i p g i i i b&i t j p t r J c n g h i g m Co hpc 12 - TrSn Trpng Hung Sail d o t o a nha p l i a n xa a m v d i a m p h a n xa c i i n g c6 t a n so' f ngirt^fi q i i a n sat diJng y e n c u n g n h a n difdc a m c6 t a n so n a y TRfCH D E = lOOHz va HOC VA CAO D A N G 2010 VA (Plian c(Mioc) ' ' m • B c u n g phifcJng e i m g I a n so C CO e i i i i g piia ban d f i u va c u n g b i e n d o I ) C l i n g p h i r d n g , c i m g (an so va eo h i e u so'pha k h o n g d o i (heo thtJi g i a n I a u 304 m a ( t h o a n g c i i a m o ( cha( l o n g c6 hai n g u o n s o n g k e t h d p A va B e a c h n h a u c m , d a o d o n g t h e o piiirifng t h a n g diVng vi'-fi pluriing t i i n h U A = 2cos40nt va U | ) - 2cos(40n;t + n) ( U A vii Uu t i n h b a n g m m , t ( i i i h b a n g s) B i e t toe 305 PhUdng phap giai bai tap trac ngtii$m C O HQC I ^ - Iran irqng Hung' uiy truyen song l i e n mal chat long la 3()cm/s Xet hlnh viiong A M N B thuoc mat iniiiil l¥l I V U t f v i i ivHuiiy Cau 13 V a t nho cua mot lac 16 xo dao dong dieu hoa theo phUdng ngang, Ihoang chat long So' diem dao dong v6i bien circ dai tren doan B M la mo'c the nang tai vj tri can bang Khi gia to'c cua vat co dp Idn bhng mpt niVa A 19 dp Idn gia to'c cifc dai thl t i so'giu'a dpng nang va the' nang cua vat la B 18 C 17 D 20 Cau M o t ific 15 xo gom vat nho khoi liTdng 0,02kg va 16 xo c6 ciriig A I vat nho diMc dat tien gia del co djnh nam ngang doc theo triic 16 xo IN/m He so'ma sat triAJt giCra gia dil \ vat nho la 0,1 Ban dau giff vat d vi t i i 16 \(, B ; C D - • Cau 14 M p t cpn lac ddn cd chieu dai day trep 50cm va vat nho cd kho'i lifdns bi ncn 10cm roi buoiig nhe de lac dao dong ta't dan L a y g = lOm/s" 'i'oc 0,01kg mang dien tich q = 5.10^'C dUdc coi la dien tich d i e m Con lac dao dp k'^n nhat vat nho dat du'de qua trinh dao dong la dpng dieu hoa dien tru'dng deu ma vectd cifdng dp dien trUdng cd dp A V c m / s B 20^/f)em/s C 10^30 cm/s D ^ cm/s Cau Dao dong tdng lidp ciia hai dao dong dieu hoa citng phiWng, cCmg tan so' c6 phu'dng trinh li dp x = 3cos Tit 5ii (cm) Biet dao dong thir nhat co Idn E = lO'* V / m va hu'dng thang di?ng xuo'ng du'di Lay g = lOm/s' va TT = 3,14 Chu k l dap dpng dieu h6a cua cpn lac la A 0,58s B 1,99s C I,40s „i^:;r , D 1,15s phiftdin B Theo chif(/nj^ trinh niins cao /• Cau 15 M p t banh da cd mpmen quan tinh dp'i vdi true quay co djnh ciia nd la trinh li X | = 5cos Tit + • v cm Dao dpng thuf hai cp phu'dng trinh li dp la 0,4kg.m" De banh da tang to'c tiY trang thai ddng yen de'n to'c dp gdc co phai to'n cong 2000J Bd qua ma sat Gia tri ciia co la B x-i = 2eps Ttt A X T = 8cos Ttt + - (cm) + - (cm) A lOrad/s 6; B 200rad/s C lOOrad/s D 50rad/s Cau 16 De k i e m chiJng hieu ting Do'p-ple, ngu'di ta bd' tri tren mpt difdng ray •^71 C X , = 2cos Tit (cm) 5Tt^ (cm) D X - 8cos xac dinh va mpt may thu am du'ng yen Biet am truyen trpng khdng vdi Cau Li/c keo \ tac dung len mot chat diem dao dpng dieu hda C P dp Idn A va hu\3ng khong dpi r;, , IV' B ti le vdi dp Idn cija l i dp va lupn hu^ng ve vj tri can bang j;^]/ ' C t i le vdi binh phifdng bien dp • A 620Hz B 820Hz C 780Hz dap T a i thdi d i e m t, chat diem cd to'c dp dai, td'c dp gdc, gia tp'c hu'dng tam va dpng lu'dng Ian lUdt la v, (o, a„ va p M o m e n dpng lu'dng ciia chat d i e m ddi vdi triic A du'dc xac dinh bdi = 10 Tan so'dao dpng cua vat la A L = p.r B L = m.r.co C L = mvr^ C IPiz D 2Hz Cau 12 T a i mpt d i e m tren mat chat Idng C P mpt nguon dap dpng vdi tan 120Hz tap sdng p'n dinh tren mat cha't long X e t gdn Ipi l i e n tiep tren mo' phirdng truyen sdng d ve mpt phia sp vdi ngupn, gdn thu" nhat each gdn t l ' " nam 0,5m To'c dp truyen sdng la A 3()m/s 306 B 15m/s D L = ma„ Cau 18 Trpng chuyen dpng quay cua vat ran quanh mpt true C P ' dinh, mpmen quan tinh ciia vat dd'i vdi true quay A phu thupc vap tpc dp gdc ciia vat B 3Hz D 560Hz D bien dp va gia tp'c trpng mpt chu k i khpang thdi gian de vat nhp ciia cpn lac C P dp Idn gia to Ig lg^=:2-loglO > ^ '40n CO • k + nen: d; - d , = ^' 2n \ 'A 40= X T V 1,5 2; V - 100 > r„ = lOOr^ - -"A ( d : - d | U , - M B - M A = 20(V2 - 1) ; ^ = 50,?r (d:-d,)„„„ = - B A = -20 L A - I.M = 201g ^ 'i = 20lg5() v > l,M = L A - 201g50,5 = 60 - 201g50,5 « 26(dB) Vay:-20 - L5£20(V2-1) k+ fl! Co HA T TI^T^T V As A • to v = = A , 3A At 2T , As = — + A = — 2 lAj, (((1 V I ' n " i ; Cau Dap an B i^: I 12 I M r ' i fi tj • Co W, + W,| = W ' 111 i I ' d ' « ( , Dat: = -mg/a(-, 72 -I ' " - • -Limg(A-x) < ^ 4—&- () (*) y = -mv"^ la mot ham so theo bien so x |.img -> i) 0,1.0,02.10 X = - — ^ = ,^ ^ 0,02 ( m ) ,.; 'I •< i' '1: ' Lucd6(*)cho: ymax Cau Dap an A 308 -, •, y: max thi y' = V d i y' = - k x + ).img = V2 so' nut = n + = ^'.^i" \na Con idc chuycn dong nhanh dan theo chieu du'dng ti?c li'ic a < 2W, = \ () ? (19 gia tri k) •< • Tai W, = W.I till: Cau Dap an D «I n k = -13 Vay 4f i>/ •' ' • ' )! -13,8 ? k < 5.0062 () Cau Dap an D I *• / f 2.1.40 , >• n = — =: =4 V 20 =^mvL,x =^.1(0,1 0.02-)-0,1.0,02.10(0,l-0,02) = 0,0048-0,0016 = 0,0032 , , 1,' - V - , , , =0,0032 -> v - , „ = , ^ v , „ „ = / a = , ^ (m/s) = 40V2 (cm/s) 309 Lty IIMHH IVIIV UVVH l^n^".j viei Phuong phap gidi bai tap trSc ngtiigm Co hpc 12 - Iran Trpng Hung \_ Can Dap lin D Co: X = X| + X: ^ -> W , = - k x ^ = - k X: = X - X ] :i Vectcfquay: X = X - X i r vdi W = - k A ^ 2 ^ •/v.-^ | » w,, = w - w, = - w Cac hinli chie'ii ciia chiing xuo'ng true difng va ngang Ian Ajsincp^ = Asincp - A j sincpi = s i n 571^ f I A-, coscp-i = Aeoscp - A , cos(P| = 3cos ^ A : = - sin ; ( 57t^ I = -4 FVay: ,< ;;au 14 Dap an D = -473 - eos P' = mg + qE 6y g = m 7t , P=- = - T = - > (p, = — hoae -4x/3 V3 ::=g + ^ = + m -4 Chi'i y rang sincpj < nen cpi = V a y x^ = 8cos(7it = ) (m/S 0,01 1,15(8) ; 57t | u 15 Dap an C 2A 2.2000 I 0,4 ) (em) _A Cau9 D a p a n B -A Cau 10 Dap an A - = 100 (ra.d/s) uTU 16 Dap an A A , , - - - ^ 1= ( r=( A S A p dung cong thiJc tong quat: f' = f o V Cau 11 Dap an C V ± VM V=FVjj V I nguon thu diJng yen (VM = 0) nen: f = f Tronsi thdi siian — v a t d i tu" - — ( h i n h ve) • 2 340 340 - = f 740 = f.340-30 310 —> Thdi gian di tCr O - > — la — CO = [6 7(-4)-+(-4N/3)- =8(em) va tancp = w, 340 340 - = f f = f.340 + 30 370 = I m / s " = (o~|x v d i x = — = - ^ ( m ) ' 2 f 310 740 370 ta dirdc VT-W f ' - (Ilz) | a u 17 Dap an A ',, nen: = ( o - - ~ - - > ( d - = , ' - (27if)' = o - > f = (Hz) '' " L = I.co = ( m r ' ) — = m.v.r = p.r '' Cau D a p a n B ' ' ' Khoang each hai gdn song lien tuc la X nen gdn lien tuc each AX V a y 4X = (),5 -au 18 Dap an C M =1 =1 CO - ) = 10 = 2,5 (N.m) 120 t ; 0-30 Nam 2011 ' A = M = ()j23(m) - - > v = ^ f = 0,l25.120== 15(m) " ^10 X , , = -co^A -> V P h a n chunj» cho tS't cii thi sinh 'au M o t chat d i e m dao dong dieu hoa tren true Ox Khi ch;ft diem di qua v] tri can bang thi toe ciia no la 20cm/s Khi chat diem c6 toe la lOcm/s thi Cau 13 D a p a n B a -^ X gia toe ciia no co Idn 40V3 cm/s" B i e n dao dong cua chat diem A I x'f A 5cm B.4cm , C 10cm ^ D 8cm 311 Cty TNiiii Miv OVVH Khang Viet Phuong phap gi4i bai tSp trSc nghi?m Co hoc 12 - Trap Trpng Hung b h n g c m , t t i n h b f i n g s) K e tir t = c h a t d i e m d i q u a \ t i i c H d o x = - e n i I a n tin? 201 t a i t h t i i d i e m A 3015s B 6030s C I C a u D a o d o n g m o t c h a t d i e m c k h o i k r d n g lOOg la l o n g h d p c u a h a i d a o C a n M o t c h a t d i e m d a o d o n g d i c i i hoa t l i c o phircJng t r i n h x = i i > s - ^ - t (\i D 6031s C a n M o t c h a t d i e m d a o d o n g d i e u hoa t i e n t r i i c O x v d i b i e n d o c m c h u k i d o n g d i e u hoa c i m g p h i f d n g c d p h i f d n g t r n i h l i d o Ian lu'di la X | = ?cosl(Jt va x^ - l O c o s l O i (\| X2 t i n h b h n g c m , t t i n h b h n g s) Mo'c t h e n a n g cf v i t r i c a n bhng C d nang ciia chat d i e m bhng A.0,112.'SJ B 225J C 112,5.1 D 0,225J C a n M o t s d i d a y d a n h o i c a n g n g a n g d a n g c s o n g d i f n g o n d i n h T r e n day, 2s Mo'c t h e n a n g d \ t i i c a n b h n g T o e d o i r u n g b l n h c u a c h a t d i e m tionx = ± 2 Cau 19 Mot vat ran quay quanh mot true co dinh, cd momen quan tinh khong ddi doi vdi true Neu momen lire tac d i m g len vat khae khong va khong ; , ^ A Thdi gian nho nhat vat di tir y AS , (ho^c A AV3 ) vdi thdi ddi thl vat se quay A vdi gia toe gde khong do'i B vdi toe dp gde khong ddi C cham dan deu rdi dij'ng han D nhanh dan deu rdi cham dan deu Cau 20 Mot dTa tron mong ddng chat cd dirdng kinh 30cm, kho'i Iu'png 500g quay gian: T At = T T ,^ = — = - (s) 12 12 d e u quanh true co' dinh di qua tam dTa la 0,03s Cong can thiTc hien de dTa dtrng lai cd dp Idn la A 820J 314 B 123J Toe dp trung blnh: v = C 493J D 246J As At 2^^-') 5(V^-1) * 21,96 (cm) 315 PhL/ang phdp giai bai tr5c nghigm Co hoc 12 - Trgn Trqng Hang tap C a n D a p a n D (^au • • Dap an = 2A cos- C ' a u D a p a n D B ' • ^ i'' " U i M = i b M = a c o s ( ( ) n t - 2n—) , ' Thcfi g i a n n g a n n h a t d e d i e m B d a o d o n g v d i b i e n d o A d i l i f AN/2 - > A\^2 - > U M = I | M = a c o s ( ( ) i t - 2n.^ ) U K , = U : , , = a c o s ( i t - T t - ^ ^ ) - > Uo = 2U|() = a c o s ( ( ) n t - ^ ^ ) la 2.1 = Vay: D o I c c l i pha giffa M va O : V = ^ - ( c l | - A O ) = 2kTt - > d| - A o - k> ;,; Acp = cpo - ' () (cni/s) = 0,5 (m/s) —» I 0,8 San M J.:.' k h i b i i o n g 16 x o t h l n i i d a o d o n g 111] m n h a n h d a n ncMi ca h a i v a t m , \ m^ n h m sat n h a u va c i i n g d a o d o n g d i e u h o a \ d i v d i X = v T = 50.0,04 = ( c m ) „ = A ( ) + A = + = I I (cm) t a n so () -'(mill) — A i ( ) -2A ^ i ! a u 10 D a p a n D - > k = : 1,2, , Vaydu - = , - > T = 0,8 (s) T > kA > ( = ' = ) - > d , „ „ „ „ - A ( ) = k,„i„A= \ ^71 ' CO I lim, nil + m (cm) \/>-'|(iiiin) r'k" k~ = V t a i v i t i i c a n b h n g C) (16 x o t r d \ t i a n g t h a i tu" n h i e n ) v d i : C a n D a p a n D V = I " +a k A, (A, = 8cm) Si-a 2,"52 5—^= — = g +a 3,15 = 3,15 0,8 - > a = — g 41 ;- S a n k h i q u a k h o i O I h l n i i d a o d o n g c h a m d a n c n v a t m^ d o q u a n t i n h n e n v a n giCf n g u y e n t o e d o v \ t i d t h a n h c h u y e n d o n g n h a n h h d n v a t n i i , d o « - a hai vat b a t d a u tach ra: 41 50 - 271 50 41' ->T= V 271.1- = j ^ , ^2,78 (s) [T n i l d a o d o n g d i e u h o a v d i t a n so' ( : = V = (O2A2 C a n D a p a n A '• X = X i + X2 = 15co.slOl Cau9 ( ) v a (2) c h o : W i A ; = (O2A2 8(cm)= I — A , - > A = 4^ = ^ ( c m ) : m, V2 l u c n a y 15 x o c c h i e u d a i ci/a d a i T h d i g i a n l i r l u c 15 x o c c h i e u d a i t i f n h i e n ( v a t d O ) d e n k h i 15 x o d a i cifa song dtrng tren day: f 2n(i 7c^ + — cos X 2j \ (Ot - — y L a y A l a m goc thi d difdc tinh tif A B i e n dao dong tai C: ac = 2A cos 2m 125 (J) DapanB I , va c b i e n d o A ; c h o b d i : ' -mw-A-=-.0,l.(10)-.(0.15)-=0.1 2 u = 2Acos II— m (2) ^ E= (1) 2m -2,.'i2 T =2n T , = 2n (0|A| = 27rdf X 71 -i— vdi < d( = A C = c m X = A B = 40cm dai la: — = — : , / — 4 k V T r o n g t h d i g i a n — v a t q u a m2 c h u y e n d o n g t h a n g d e u va d i d i f d c : n T S2 = V - = 2m, k 2V k A,.71 2V2 87T 2V2 = 2V2,7t ( c m ) 317 "rnmtig pna'p'OTar'TOTiaprai; ngnieiti Lo iiyu i ^ - imii iiyiig nuiiy Khoang each hai \at: As = S2 - AT = 2\[2.u - \ / =3,2 (cm) Can 11 Dap an D — — r,'1 '1 J Can 12 Dap an • • T= phu thupc viio khoang each d niiid tarn ciia vat ran den true Can 16 Dap an C B X - + t = 0, I quay Vlu T= ^ = 0,314-^(0 = ^ ^ - ( r a d / s ) iOO 0,314 A= 27t —f • I, • Can 15 Dap an C X = 2^ + - 2cm, V< 40N/3 C(S: -(0 -CO2) = I(C0| M L,-L L , - L • = —>y[ t = — - t— - = 1=9 1= Ap dung cong thiYc Acp = ^yt^ +(o,)t K ->(p = - Trong 9s dau (tiV t = -» t = 9) vat quay diTdc: A(p= - = 126(rad)nen: 126= ^ Y ' + ( O O sincp > Vay: x = 4cos 20t + = -1,4 (cm) • B t = l() Giay tliif 10 V = -(oAsin(p < 1,5 — B Cau 17 Dap an COS{p = — 3-0,9 Vay | M | = 1,4 (N.m) = cos (p Can 13 Dap an CO, I L| - L T = 4(cm) 20 M =I.Y = I (I) Trong Os da u (tij" t = -> I = 10) va t quay difdc 150 rad: 150= -y.Ur (2) + 10.(0o % - mg(3cos(x - 2cosao) ^ i m x =mg(3-2co.sa()) mg(3-2cosa„) ^ V = , 200 ' , (cm/s) • k+ k+ 2 200 70< v = -(em/s) < 100 k+ I , < k < — = 2,3 - ^ k = 14 Vay V = — 3,02 a o « 6,6" B Hai diem ngu'dc pha each nhan: d = , Cau 18 Dap an -> - 2cosao = 1,02cosao -> cosuo = Can 14 Dap an (1) va (2) cho: = 1,02 l ^ 2J ' \ ^ 2J / = /„ Jl ^ , ^ (Oo = (rad/s) = 9^ 126-9(0,) , , -63(11/.) \ 2f' ^ v = 80 (cm/s) 2,5 318 319 MXJCIAJC ('lii('