GiSi Chu k i dao dong r i e n g cua mach dao dong dien tiX L C : T = 27IVLC K h i dien dung t h a y doi tii C i den C t h i chu k i dao dong r i e n g thay doi tii InyJLC, den In^lhC^ Vay chqn dap an D Cdu 46: M o t v a t dao dong dieu hoa c6 16n v a n toe cifc dai l a 31,4em/s Lay n = , Toe t r u n g b i n h cua v a t t r o n g m o t ehu k i dao dong l a : A B 15 cm/s C 20 cm/s D 10 cm/s Giai Vdfi V = CO A, t a c6 toe t r u n g b i n h cua v a t t r o n g m o t chu k i dao dong l a : 4A v =T 4A(0 2Aco 271 71 2V = 20(cm/s) 71 Vay chqn dap an C Cdu 47: M o t chat phong xa b a n dau c6 No h a t n h a n Sau n a m , l a i m o t p h a n ba so h a t n h a n ban d a i chiia p h a n r a Sau n a m nufa, so hat n h a n ,c6n l a i ehifa p h a n r a cua chat phong xa l a : B3 16 Giai Goi No l a so h a t n h a n ban dau, So h a t n h a n l a i sau n a m l a : t 2T =3 Sau n a m nffa, so h a t n h a n l a i chtfa p h a n r a : N N„ N„ N„ 2T Vdy chgn dap an A Cdu 48: M o t lac 16 xo gom 16 xo nhe va v a t nho dao dong dieu hoa theo phUcfng ngang v d i t a n so goc 10 rad/s B i e t r a n g k h i dong n a n g va the n a n g (mo'c d v i t r i can bSng cua v a t ) b k n g t h i v a n to'c cua vat CO I6n b k n g 0,6 m/s B i e n dao dong cua iSc l a : A 12 cm Gi4i Chi tiet B V c m thi TS BH, CD Mon Vat l( C cm D ^ cm 47