Theo d i n h luat bao toan nSng lucfng, t a c6: - +2C— cu^ =- q = ^ C ' U ^ - C L i ' =8.10-'° (C) Vdy chgn dap an D Cdu 35: H a t n h a n ^^gRa bien ddi t h a n h h a t n h a n ^g^R" p h o n g xa: A p \ a va p " C a Ta CO phircJng t r i n h : -fgRa ^ D p" 'g^Rn+ 2He ^He la h a t a Vdy chgn dap an C Cdu 36: M o t c h a t d i e m dao d o n g d i e u h o a X = 3sin 6J theo phiTcfng t r i n h (x t i n h bang cm va t t i n h b ^ n g giay) T r o n g m o t giay dau t i e n tCr thcfi d i e m t = 0, chat d i e m d i qua v i t r i c6 l i x = + 1cm: A I a n B I a n C I a n D Ian , GiSi Chu k i dao dong: T = — = 0,4s N g h i a la t r o n g I s , v a t thufc h i e n CO 2,5 chu I d T r o n g m o t chu k i , v a t d i qua v i t r i c6 U x = + l c m h a i l l n nen t r o n g I s , v a t d i qua v i t r i c6 l i x = + l c m n a m I a n Vdy chgn dap an C Cdu 37: M o t song ccf Ian t r u y e n t r e n m o t dLforng t h i n g tii d i e m O den diem M each O m o t doan d B i e t t a n so f, budc song X vk b i e n a cua song k h o n g doi t r o n g qua t r i n h song t r u y e n N e u phi/cfng t r i n h dao dong cua p h i n tuT v a t chat t a i d i e m M c6 dang UM(t) = asin27tft t h i phifofng t r i n h dao dpng cua p h a n tuT v a t chat t a i O 1^: A U o ( t ) = asinjr B U o ( t ) = asin;c C U o ( t ) = asin23i D U o ( t ) = asin2;i ft4 Neu phifcfng t r i n h dao dong cua p h a n tijf v a t chat t a i d i e m M c6 # d dang U M ( t ) = a sin Inft t h i t h d i gian t r u y e n song tCf O d§n M 1^ At = — Gt&i Chi ti^t d l thi TS OH CD M6n V$t II I 17