Cdu 55: M o t v a t r S n quay n h a n h d a n deu quanh m o t true co d i n h dudi tac dung cua m o t momen life M Bo qua m o i life can N e u t a i thofi diem v a t C O toe goc co, ngCfng tac dung momen life M t h i v a t r S n se A quay cham d a n deu r o i dtrng l a i B quay deu vdri toe goc co' < co C dCfng l a i D quay deu v6i toe goc ct) Giai N e u t a i thcfi d i e m v a t co toe goc co, ngOfng tac dung momen life M t h i v a t r a n se quay deu vdri toe goc co Vdy chgn dap an D Cdu 56: M o t mSu chat phong xa co chu k i b a n r a T d cac thcfi diem t i va t2 ( v d i t2 > t i ) ke tCf thori d i e m b a n dau t h i phong xa cua mSu chat tifcfng ufng l a H i va H2 So h a t n h a n b i p h a n r a t r o n g khoang thcfi gian tCr t h d i d i e m t i d e n thofi d i e m t2 bang: ^ (H,-H,)T ln2 g • H,+H, ^ • 2(t2-t,)' (H,4H^)T • ln2 ^ • • (H,-H,)bi2 T ' Gidi T a c o : H , =A.N,; =?.N2 ^ A N =N,-N^ = X, In Vdy chgn dap an A Cdu 57: Cho p h a n ufng h a t n h a n ' L i ^ H e + i H e B i e t k h o i li/cfng cAc h a t dorteri, l i t i , h e l i t r o n g p h a n ufng t r e n I a n li/oft l a 2,0136 u; 6,01702 u ; 4,0015 u Coi k h o i l i i O n g cua nguyen tuf b k n g k h o i Icfgng h a t n h a n cua n o N a n g lifcfng toa r a k h i co g h e l i diigfc tao t h a n h theo p h a n ufng t r e n l a : A 3,1.10''J B 4,2.10'°J C 2,1.10^T D 6,2.10"J Gi^i Tac6:Wt6a= ^N„(mo-m)c^ = - - , " (2,0136 + 6,01702-2.4,0015).931,5.1,6.10-" ^ = 3,1.10"J Vdy chgn dap an A 150 Gi4ichiti«t(3«thiTSDH, CBMftnVatIi Cdu 58: M o t v a t rSn quay deu quanh m o t true eo d i n h xuyen qua v a t Mot d i e m t r e n v a t r S n eaeh true quay em eo toe d a i l a 1,3 m/s Toe goc eua v a t r a n c6 \6n l a : A 5,2 rad/s B 26,0 rad/s C 2,6 rad/s D 52,0 rad/s Giai v T a e o : co = - = = 26rad/s r 0,05 Vdy chgn dap an B Cdu 59: T r o n g m o i triJcimg t r u y e n a m , t a i h a i d i e m A va B c6 mufe CLfofng a m I a n luot l a 90 d B va 40 dB v d i eung ei/drng a m chuan CUcfng a m t a i A \dn gap bao n h i e u I a n so vdfi cifotog (Jp a m t a i B? A 2,25 I a n B 3600 Ian C 1000 I a n D 100000 I a n Giai T a c o : L A - L B = 1 g - ^ = 50 ^ ^ = 10'= 100000 I a n • h Vdy chgn dap an D Cdu 60: T r o n g t h i n g h i e m Y-ang ve giao thoa a n h sang, chieu a n h sang t r S n g vao h a i khe T r e n m a n , quan sat t h a y : A chi m o t dai sang c6 mau nhiT eau vong B he v a n gom nhCifng vach mau t i m xen ke v i nhOfng vach mau C he v a n g o m nhffng vach sang t r S n g xen ke v d i nhuTng vach t o i D v a n t r u n g t a m l a v a n sang t r a n g , h a i b e n c6 nhOTng d a i m a u nhif cau vong, t i m of t r o n g , d ngoai Giai Trong t h i nghiem Y-ang ve giao thoa anh sang, chieu a n h sang t r ^ n g vao hai khe T r e n m a n , quan sat t h a y v a n t r u n g t a m l a v a n sang t r a n g , h a i ben eo nhufng d a i m a u nhif cau vong, t i m d t r o n g , or ngoai Vdy chgn dap an D Gik\i tiet d« thi TS DH, CD M6n v a t If 151 D E THI T U Y E N SINH DAI HQC NAM 2012 Mon: VAT Ll'; Khoi A Thdi gian lam bai: 90 phut Cho Met: h a n g so P l a n g h = 6,625.10~^^J.s; lorn dien t i c h nguyen to e = 1,6.10~^^C; toe a n h sang t r o n g chan k h o n g c = 3.10^ m/s; so Avogadro N A = 6,02.10^^ m o r ^ I PHAN CHUNG C H O T A T C A THi' SINH (40 cau, tCrcau den cau 40) Cdu 1: M o t l^c 16 xo gom 16 xo nhe c6 cufng 100 N / m va vat nho k h o i lirgrng m Con iSc dao dong dieu hoa theo phtfong ngang v6i chu k i T B i e t d t h i d i e m t v a t c6 l i d6 5cm, d t h i diem t + — vat c6 to'c 50cm/s Gia t r i cua m b k n g : A 0,5 k g B 1,2 k g C 0,8 k g D 1,0 k g Giai Tai thdi diem t : x i = Acos(cot + (p) = 0,05m T a i t h i d i e m t + —: X2 = A COS 71^ cot + (p + — 2) V = - coA sm l^fot + (p + — = - a ) A c o s ( ( o t + (p) = ± , m / s Suy r a : ( O = 10 rad/s => m = k g Vdy chqn dap an D Cdu 2: M o t chat d i e m dao dong dieu h6a v6i chu k i T Goi V T B la toe t r u n g b i n h cua chat diem t r o n g m o t chu k i , v 1^ toe tufc t h i cua chat d i e m T r o n g m o t chu k i , khoang t h d i gian m a , v > ^ v ^ l a : A I B C T D.I GISI V > - VT-B = ^ = — tifong iJng vdri l i do: - — < x < — 152 Giai Chi