G.V NGUYỄN HỮU LỘC CHUYÊN ĐỀ VẬT LÝ 12 CÁC PHƯƠNG PHÁP GIẢI BÀI TẬP VÀ TUYỂN TẬP ĐỀ THI ĐẠI HỌC QUA CÁC NĂM LƯU HÀNH NỘI BỘ 2011 PHẦN I: A/ PHƯƠNG PHÁP GIẢI: I/ DAO ĐỘNG ĐIỀU HÒA VÀ CON LẮC LÒ XO – 1 – Kiến thức cần nhớ : – ω+ !"#–ωω+ !"–ω 2 ω+ ! –$%&'()* ++–,-.!" –+ ++,!" 2 +  . . + α  +.   . +    . − /  2 +   . . − α –0&' ω . 1 π .,2 2 – Phương pháp : –3*45 5ω666 –7*#89:*&'()*/ –*#;<=5 5ω666// –>=*?@@9 –1=A#B*    ! #    ! = ω + ϕ   = − ω ω + ϕ  ⇒ A A  #    ⇒0*?@@9 / 3 – Phương trình đặc biệt. –Cω+ !#;⇒      –C 2 ω+ !#;⇒DE  . "ωF.ω" F. / 4 – Bài tập : a – Ví dụ : 1.0G<498H / ! ω+!ID/ω+ ! !/I0/ω+ !+/I!/ω +!I/ 1J5ω5(BKL%/0*() ! 5 ! =MN:/ DE 1GO10D 1G#4@EC HD :>*#;#B9PQJω+ !+/I!/ 0G0/ 2.9R#J9ω!/SR9L ET /A/ D/,-./ 0/,/ /.,/ HD :7*#89ω,-.! = ,-./ 0G D/ 3.9J9ω/U%:(B(V# /J(+/ D/J(/ 0/WO10DN89/ /WO10DN8XI/ HD : 1=A#B)+ 0G b – Vận dụng : 1.1*B?&<498HT /Y,+I!/ D/ZAA,+,-[!I 0/. 2 .,+,-[!I/ /ZY,+ZY,I!/ 2.9R#J9 2 ω+,-\!I/0G?(VT /O9#;E-./ D/O9#;E/ 0/O9#;E./ /O9#;S,-\/ 3.9R#J9Y,+Y,I!/E9R# (B /-./ D// 0/ . / / Z / 4.9J9ω+,-Z!/U%:(B(V#J /(-.5=<N89 D/(-.5=<N8 XI 0/(-.5=<N89/ /(-.5=<N 8XI 5. ;*9]RI(^J9_A5`Y,-.!/OJ?%()I\AA59 8H/DE9R#(B /Z.I/ D/.AI/ 0/.I/ /`I/ .–0?a9 1 – Kiến thức cần nhớ : –bEW;%(B9:1   "2   "ω .   π       –bEW;9cd(R(H 1., I ? = ( 1 .  ( 1 .    ∆ = π    ∆  = π  α  . #;d(  A ( ( − ( A 089B^ER(H! –bEW;^=M?%()I –>%9  –1: (e(HNf ' (e(HLI E   . . I 1 . ? I 1 . ?  = π     = π     ⇒   . .   . . . . I 1 \ ? I 1 \ ?  = π     = π    ⇒ . . . Z Z  . Z Z  . . . . \ \  . \ \  . I I I I 1 . 1 1 1 ? I I I I 1 . 1 1 1 ?  = + ⇒ = π ⇒ = +     = − ⇒ = π ⇒ = −   –bEW;^=M?%()? Ug(H + %  .    ? ? ? = +  ⇒1 . h 1  . i1 . .  +>??  +? . ⇒ . . .  .    1 1 1 = + 2 – Bài tập : a – Ví dụ : 1.0(e(HjI#I#B(H?98H5?IeEI#B#II#?* J?%()kZ(S#I?9RV !l(EZ(S !mIZ(S !l(E.(S 9!mI.(S HD :Chọn C.0?9R(e n I I ZI \I 1 . "1 . . ? ? ? + = π = π = π n 1   1 . ⇒ = 2. oN#I#B(H?(Hc.5YI5?@@I9/0?9 ^9R#(B !/ !A5Y/ !A5Z./ 9!A5.`/ HD :Chọn C.1#4@XLG(^*9]#B#XL#;(^BjR(B A A ( I I ? ( ?  ∆ = ∆ ⇒ =  ( ) A ( . I A5A.Y 1 . . . A5Z.  ?  A ∆ π ⇒ = = π = π = π = ω 3. $(e(H9f'/OJ?%()IhA5.?/1.A(e^ Q)YA9/1@'R(H/ ![A-I! !\A-I! !YA-I! 9!YY-I! HD : Chọn C.1.A(e^Q)YA9EmJ1   A5\ $P?*J I 1 . ? = π . . . . \ I \/ /A5. ? YA - I! 1 A5\ π π ⇒ = = = / 4. p(HJ89BL''(B?  5? . /oIe#I#BI(H?  5 #I9#;?1  A5[/oIe#I#B(H? . 5#I9#;? 1 . A5`/oIe#I#BQ(H?  #;? . ?9RI(B/ !A5\` !A5q !5AA 9!5\ HD : Chọn A 0?1  51 . *4r   . . I 1 . ? I 1 . ?  = π     = π    .  .  . . . . \ I ? 1  \ I ? 1  π =   ⇒  π  =   . . .  .  . . .  . 1 1 ? ? \ I 1 1 + ⇒ + = π ?  5? . g5'RQg*4r&'??  +? . /0?9R (e(Hg ( ) ( ) ( ) . . . . . .  .  . . . . . . . .  .  .  . 1 1 1 1 I I A5[ /A5` 1 . . . I/ A5\`  ? ? ? A5[ A5` \ I 1 1 1 1 = π = π = π = = = + + π + + b – Vận dụng : 1. oe#J?%()I  \?#BI(HJ?%()?&*?<5J9 #;?1  /oeI#?*J?%()I . #B(HEJ9#;??1 . A5Y/o%()I . LET !A5Y? !.? !? 9!Z? 2. $(HJ'?Ie#;#PI  J?91  5`/Ie(HJ#; #PI . ?9(B1 . .5\/1I?9?gI  #BI . #;(HJ E !.5Y !.5` !Z5[ 9!Z5A 3. p(HJ89BL''(B?  5? . /oIe#I#BI(H?  5 #I9#;?1  A5[/oIe#I#B(H? . 5#I9#;? 1 . A5`/oIe#I #BQ(H?  g%? . ?9RI(B !A5\` !5A !.5` 9!\5A 4. $(HJ'?h.Y-I!/$SR(He#B<Is%4/ 1N#B(H#J ?%()IhAA#B∆Ih[A/1@9cR(H?#XL#BS% J9R(e/ ! ( ) ( ) A ( \5\ I " .5Y 9-∆ = ω = !d( A [5\I"ω.5Y9-! ! ( ) ( ) A ( [5\ I " A5Y 9 - ∆ = ω = 9! ( ) ( ) A ( [5\ I " Z5Y 9-∆ = ω = 5. 0(e(HjI(H?#B#I598H#;?1/$%S%9 R(e(B2 F A5Ypt?%()R#Im(B !I F .I !I F ZI !I F \I 9!I F YI 6. bS()N#I  #BI . #BI(HJ'?\A-I#B?@@V9 /1uI?m:k45I  ^Q.A9#BI . ^QA 9/Nm##B(H?9RQLπ-.!/o%()I  #B I . (S()LE !A5Y?"? !A5Y?".? !?"? 9!?".? 7.198HRI(e(H5mI?%()R#P.Av% (S9R(eI#4: /l Y -.(S/ D/l Y (S/ 0/mI-.(S/ /mI Y (S/ I I∆ Z–3*4*9R#w:<I#BF+d 1 – Kiến thức cần nhớ : –1*9R#w:<I .    ! #   !    !  = ω + ϕ  = −ω ω + ϕ   = −ω ω + ϕ  pQ'(   2  .   + .  . # ω 0&'  ω 2  –0=<9S#/> A –0=<I9S#/< A 2 – Phương pháp : x0*;mB*I(5#%9w:<I –0*Thay t vào các phương trình : .     ! #   !    !  = ω + ϕ  = −ω ω + ϕ   = −ω ω + ϕ  ⇒5#5/ –0*.sử dụng công thức :  2  .   + .  . # ω ⇒ 1 C . .  . #  − ω  2  .   + .  . # ω ⇒# 1 Cω . .   −  x0*;mB*I(5#%9;!:<II?m :∆/ –D:<I#J( A / –1r98B=ω+ != A –bk=QIω+ =α#; A ≤ α ≤ π '#;mI#=<N8XI# #<A! P ωi =yα '#;l#=<N8 9! –b#B#%9;!:<IJ∆X=(B     ! #   ! = ±ω∆ + α   = −ω ±ω∆ + α   P    ! #   ! = ±ω∆ − α   = −ω ±ω∆ − α  3 – Bài tập : a – Ví dụ : 1. $k<I=<EfJG#B%(EQ#;w< '.YI- 2 !0?#BS%JRk<I(B /5.Y[".Y9-/ D/"Y9-/ 0/."Y9-/ /5.Y["Y9-/ HD :>*#;ω 2 / 1Jω 2 .Y⇒ωY9-51 . π ω 5.Y[/ 0G/ 2.$#98HJ..,–,-[!I5!b#B#%R #(VA5.Y(B /I"C. Z ,/I-!/ D/5YI"C, Z I-!/ 0/A5YI"C Z I-/ / I"C,I-/ HD : 1r..,–,-[!I5!⇒#\,.,–,-[!I-/ 1=A5.Y#B#B#5)I5#C. 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D.bVA A `I"# A AO)8+r#4@E9! DZOWO10DA5#< A M, t A M’ , t #< 0  A  #< 0 #> 0  A O A −A M 1 x M 0 M 2 O ∆ϕ A −A M 1 x M 0 M 2 O ∆ϕ D\OWO10D5'#;#=<H8W$ 0 #B$ 1 /O A5#k* r$ A E:<I'k#WO10D'#;#W$ 1 /oJ*?@WgJ∆  . π ⇒ ∆ϕ ω  A Z[A ∆ϕ 1  \ / 2.$#98HJ`A,/1:<I#W#4@\(S '.AAƒ?<r:<IeS9(B / [A.Y ZA !/ D/ [.AY ZA ! 0/ [.YA ZA ! / [5A.Y ZA ! HD :1^QN*;J 0* x  ? A  ?.  ?  Z ZA Y  \     ? A  ?.  ?  Z ZA Y π   π = + π = + ∈   = ⇒ ⇒   π   π = − + π = − + ∈     OW(S'.AAƒ(„!'#;#4@$  #<A⇒>A5GQIE #; .AAƒ  ? AA\ . − = =  ⇒   ZA + AA\ Y  [A.Y ZA  0*. bVA A `I5# A A OW\(BW$  #B$ . /OW=#H?a!W\(B.(S/…(S'.AAƒ mW=AA\#Hjr$ A $  / UJWg  [A.Y AA\/.  AA\ !/A5.  Z [ ZA π ∆ϕ ∆ϕ = π + ⇒ = = + = ω / 0G b – Vận dụng : 1.$#98B#;\\π+,-[!I/1:<I'Z#W#4 @.IN89/ !ƒ-` D!-` 0!Y-` !5Y 2.O98HJY,I5!/OWO10D(S'Z#B: <I /.5Y/ D/./ 0/[/ /.5\ 3.O98HJ\.,-,!I5!/O<IE9 D+\!(S'Y#B:<I/\5Y/ D/.5Y/ 0/  ./ /A5Y/ 3.$#98HJ[,,-.!I5!/1:# r O10D(VW<IJZI(S'Y(B/ [ [ / D/ ƒ Y / 0/ .Y [ / / Zq [ / 4. $#77p#;\\π+,-[!I/1:<I'.AAƒ#W#4@ .I?<rA5(B ! .A\ƒ .\ / D! .A[  .\ 0! .A.Y  .\ !7**?* 5. $#98HJ`A,/1:<I#W#4@\(S '.AA`N8XI?<r:<IeS9(B / .A\Z ZA !/ D/ A.\Z ZA ! 0/ .\AZ ZA ! / .\ZA ZA ! 6.0(e(H98BEIPf#;?1 5Y5E\I5 S(BY,-[/1@r(VA5#J.I(S'.AAY#B:<IB /YAZ D/YAZ5.Y 0/YA.5.Y /YAZ5ZqY Y–O98H– 3*4*PRI77p/ 1 – Phương pháp : x0GQW= -1]s666 -U%GO10D -089666/ -U%:666 x9J9 ω+ !I x#% #-ωω+ !I- x% -ω 2 ω+ !I- 2  1 – Tìm ω x781525?5I55∆( A -ω.,2 . 1 π 5#;1   ∆ 5–1M%9:d (B(e(H LI N f' ω= ? I 5?-I"I?! ω= A  ( ∆ 5?∆( A  I ?  .  ω / 785#55 -ω . . #   −     I    I #  2 – Tìm A x78'#;# ⇒ h . . #   ! / + ω -#A&†! ⇒  -## I ⇒A ⇒  I # ω x78 I  ⇒  I .  ω x7889BW‡0 ⇒ = 0 . / x78(^_ I ?/ ⇒ = I _ ? / . HỮU LỘC CHUYÊN ĐỀ VẬT LÝ 12 CÁC PHƯƠNG PHÁP GIẢI BÀI TẬP VÀ TUYỂN TẬP ĐỀ THI ĐẠI HỌC QUA CÁC NĂM LƯU HÀNH NỘI BỘ 2011 PHẦN I: A/ PHƯƠNG PHÁP GIẢI: I/ DAO. –0=<I9S#/< A 2 – Phương pháp : x0*;mB*I(5#%9w:<I –0*Thay t vào các phương trình : . 