SỞ GD& ĐT NGHỆ AN KỲ THI CHỌN HỌC SINH GIỎI CẤP TỈNH LỚP 12 NĂM HỌC 2010 - 2011 HƯỚNG DẪN CHẤM ĐỀ THI CHÍNH THỨC  VẬT LÍ LỚP 12 THPT – BẢNG A Hướng dẫn chấm gồm 05 trang Câu NỘI DUNG Điểm 1.1a (1,5đ)    x A c t ω ϕ = +     K rad s m ω = =              x cm Ac cm t v A cm ϕ ϕ π ϕ = − = − =    = → →    = = =        x c t cm π = + 0,5 0,5 0,5 1.1b (1,5đ) !"#$%&'cm ()(#*(+#,-.()(/0(/12#$%& #*34560       t t T − = + 78t 2 #9560#$%&'cm #*3 !%)(:560#$%&'cm#* 32;< 7=(>/(16? 560@*/-#A(#$%&'cm#* 37=(>/0(    B    C '  CM OM t ω π π π = = − =  '   D t s π → =  E560#$%&'cm#*3#9  '  DF G   D  D t s π π π = + = 0,5 0,5 0,5 1.2 (1,5đ) + HA((0)24 !IJ(K7#$ %@-404 2'  mg l m K µ ∆ = = !"(!IJ(K7.</(79(L/(/6(K72-/7 .M#A(#$%&2'00!IJ#9@,)N7:OI  2#A(7)09 #$%P2'00!IJ#9@,.MN7:OI   Q.<#/@M9R#S2OS(M04(T(4/ 0U#*>/N#9VW79@V %  2'  m mg x m K µ ∆ = =  XW((K7Y(L/#*3G3787>/!IJI  =(L/ )#*32).<:#/@M9R#SS(  [ ]   G % % % %              C   C  m m m m mvKA K l mg A A x A x A x A x l µ ∆ − + = = + − ∆ + − ∆ + − ∆ + − ∆ − ∆ G 2D'  v m s→ = 0,25 0,5 0,25 0,5 2a (1,5đ) Z#[(.(K4060()(\2J]4  79  #9 0,5     ^' ^  _ _ _ O C 1 C 2 x       d d π π ϕ λ ∆ = − + 78 C C   v cm f λ = = = !4#9(T(4-/             G d d k d d k π π ϕ π λ λ ∆ = − + = → − = − /(\J,      D``D G AB d d k AB k λ − < − = − < → = −  !,4\J(C60(T(4 !4#9(T(6/              G d d k d d k π π ϕ π λ λ ∆ = − + = + → − = + /(4\J      D``D G AB d d k AB k λ − < − = + < → = −  !,4\J(C60(T(6/ 0,25 0,25 0,25 0,25 2b (1,0đ) !460/(\J()(/60a04x2([/5(K #9   d d x− = Z60/(4\J3,M0P           G G  d d x k x k λ λ − = = + → = + 78 D``Dk = − E % 0  C D  F2Cb'  G   C   2Cb'  G  m x cm x cm  = + =     = + =    0,25 0,25 0,5 2c (1,5đ) YS.4()(\2J]4  79  #9                G G M u c d d c t d d mm π π π π ω λ λ     = − + + + +         a60  79  L//(0=#.\2J#90,/60,      AM BM AM BM b+ = + = c/.(K  79  #9         C   C G G     G2'   C G G M M M M b u c c t u u b u c c t π π π π ω λ π π π π ω λ      = + + +           → = −       = + + +           !4560         M M u mm u mm= → = − 0,5 0,75 0,25 3 (4đ) de*W 'f Hz= "    AM AB MB U U U= + (3fU AB 7/.78U MB ,4\J16(3 g79I271U AM 7/.U MB  g79(//*(M0H271U AM 7/.U MB  (//*(M0H79<[I271U AM S(.U MB  (/(M0([h/*79[h/*g271(#[(.]U AB 79 U MB #9(i  E24\J(6(3(/(M0([h/*2T(M0H79<[I deMR.j(3<[2k(3(/(M02H e 'f Hz= 2"      `  C C MB r L L C L C U V U U U U U Z Z= = + = → < → < l"1R*W#,>/)'HzZ L RZ C M02-#A(Z L = Z C $[ [/<084(T(42m#9R*W#,>/)'HzIR2) E21MR9@:#4 deMR.j(3(/(M02H79.k(3<I e 'f Hz= 2([          C  C   C     C C AM r L L r AB r L C U V U V U U U U V U V U U U U   = =     = + = → =     = = + − =      C ' C   ' C   ' C 2' C    '  ' C L Z C F Z L H r r π π −   = Ω =     → = Ω → =     = Ω = Ω     El"#A( 'f Hz= %M(h2n 0% opg,-/Rq#,>/)'Hz nM0M0P .j(3(/(M0( ' ` 2' C   r L H π = Ω = 79.k(3 < C   ' C C F − =   0,5 0,25 0,25 0,25 0,25 0,25 0,5 0,5 0,75 0,5  4a (2đ) !,/(T(K"/1O     2'  R f cm n = = = − −  Zr1M()(]779M#9l2(         l d d d ld lf f d d  = +  → − + =  = +   ' Z6.'([02(*L/1[  G  G s l lf l f cm∆ = − ≥ → ≥ = 2 "/o%M1   Gd d f cm= = =  E@*/M()(701M  C C F  C  l cm= + = − e:((/6"/1O%72-7:O"/1O()(7Gcm1M 0,25 0,25 0,5 ()(lM0-):l min =scm2/:("/1O%,01M()( lR-  C b C b '    l cm + = + + = −  >/P5:((/6(KM  0  0 F s ' s '' s l l l l cm= − + − = − + − = 0,5 0,5 4b (2đ) ct4M     O L AB A B A B→ → !(    C C  D  C  d cm d cm= → = = − eM()(]"/1O#9x2#4(      D F d x d x d x  = − = −   = −   D u>/[#9M2,\  J  #97MW78"/1OH79\  J  (v(L/ \  J  23(M\  J  S((L/\J7\  J  S((L/\J2=/ W.4M>/[           F    G  G C  C D f d x k k k x cm f d d x − = = − = − → = − → = − − − !x oCcm79D(    C ` D d cm d cm= − = 2/          CD D  C D d d f cm d d − = = = − + − +  0,25 0,5 0,5 0,25 0,5 5(2đ)  w  ! w o  DUu AB →= 0 x 2( y D 2  z   ` UCqUuuuu MMBAM =→====→  z  MB uTt G <<  x 0 y    → U ,D 1 0 x / w I  . z , w >/I  7 y / y  1. z , w >/D 1  w ( 2( z    UCqq =+− b ! w o!G  =+→= MBAMAB uuu s`1, z  w .7 y { y  w o!G w (         > + = < + −=       CC UC u CC UC u Mb AM F,L/@:("0 c/o!G x (, z  w  x  w 2, y /@ w (| z 02( z $>/<#9t "2,  ((       tUCCtICCtUCCqCqC tUCCuCCuCCtUuu MBAMMBAM ωωϕωωω ωω −=++−⇔−=+→ =+→=+                      C C U I q q c t a C C U C C i t q q c t a C C ω ω ω ω ω ϕ  = = +  −  + → → = →   = + +   =                   ( d ( AM MB C U q a u t C C C C C U q a u t C C C C ω ω  = = +  +  →   = = +  +  0,25 0,25 0,25 0,5 0,25 0,25 ! w o!Gd x 0 } F, w (        = + = + −         C a CC UC C a CC UC 7 y d(  ( )        + + + = − + =       ( ( CC UC t CC UC u t CC UC u Mb AM ω ω " `  AM MB u u t≤ ≥ ∀ ,1Y: L/@:("0 0,25 6 (1,5đ)) + !8(-O(5$[(4>/ 51O(K7$$,79.*($#4(K .O8           C  C  C C     C  I I I I I r R I I I I r R π π π π π  + =  =    + →   = =   =   +  + $|(|@V100=(K#T(?)(<#, 7$|(|@V7800=(Ki#T( dZ6O00=#T(?)(<#,7$2%=0787$| ^7$3"Ws($[(5n2(4S((L/10tt2 (00=#T(?      M I B r c π α = ^7$|3#97$|t07$$879;7$$,78(5 n  (4=(L/(v(L/10tt>/451O7$$, =.*7$|82(00=#T(?     2'  M I B r c π α = − d0=(Ki#T((K1/ G         p M r g r r g r π ρ α ρ α = + ZL/1[(|@V      G       2'   p M M M r g r B r I I c π ρ α π α = + → + = −   →    2'  C s    G   s C   − + = = + + + B I I B I g g π π π α π ρ π π ρ 0,25 0,25 0,25 0,25 0,25 0,25 Chú ý : Nếu học sinh giải cách khác đúng vẫn cho điểm tối đa A B C 1 C 2 M D 1 D 2 H.2 B ur α n P r n  n  . GD& ĐT NGHỆ AN KỲ THI CHỌN HỌC SINH GIỎI CẤP TỈNH LỚP 12 NĂM HỌC 2010 - 2011 HƯỚNG DẪN CHẤM ĐỀ THI CHÍNH THỨC  VẬT LÍ LỚP 12 THPT – BẢNG A Hướng.   C  m m m m mvKA K l mg A A x A x A x A x l µ ∆ − + = = + − ∆ + − ∆ + − ∆ + − ∆ − ∆ G 2D'  v m s→ = 0,25 0,5 0,25 0,5 2a (1,5đ) Z#[(.(K4060()(2J]4