Gi^i V i lac dcfn va Ike 16 xo dao dong dieu hoa vdri cung t a n so nen chung cung chu k i : T, = 271 - = T , g =271 - ^ - = - = > m = k - = - - — = 0,5kg Vk g k g 9,8 Vdy chqn dap an B Cdu 57: M o t v a t r ^ n quay quanh m o t true co' d i n h dvCdi tac dung eua momen life k h o n g d o i v a khae khong T r o n g triforng hcfp n a y , d a i liftfng thay doi l a : A momen quan t i n h eua v a t d o i vdri true B momen dong lifgrng cua v a t d o i vdfi true C k h o i liTgfng cua v a t D gia toe goe cua v a t G\k\ V a t r a n quay quanh m o t true co d i n h difdfi tac dung eua momen lire khong doi va khae k h o n g t h i momen dong lifofng cua v a t d o i vdri true thay doi Vdy chon dap an B Cdu 58: M o t nguon p h a t song ca dao dong theo phUcJng t r i n h : u = 4cos 47rt- 71 (em) B i e t dao dong t a i h a i d i e m g a n n h a t t r e n It cung m o t phtTcfng t r u y e n song each 0,5 m eo lech pha la — Toe t r u y e n cua song l a : A 1,0 m/s * B 6,0 m/s C 2,0 m/s D 1,5 m/s Giai Do lech pha giCifa h a i d i e m : A(p = 27i — = — =>X, = 6d = 6.0,5 = 3m X Theo de b a i : co = 47i f = 2Hz Toe t r u y e n song: v = Vdy chqn dap an B Giai Chi l i e t d e t h i TS OH, CD MSn Vat II = 3.2 = 6(m/s) 51