Cdu 8: M o t chat d i e m dao dong dieu hoa vdri chu k i T T r o n g khoang thcfi gian n g a n n h a t k h i d i tCr v i t r i b i e n c6 l i x = A d e n v i t r i X = -A A , chat d i e m c6 toe t r u n g b i n h l a : 3A 2T B 6A C 4A D 9A 2T Giai Gia sur phi/cfng t r i n h dao dong l a x = A cos cot T a i thcfi d i e m to = t h i x = A T a i thori d i e m t t a c6: A X = Acoscot = ^ T 2n 2n cos—1 = — < ^ T T Mac khac S = A - A 231^ A c o s — t = ' 2K T = — =>t = 3' A^ _ A • 2j 3A V V a n toe t r u n g b i n h ~ = ^= j OA = ^ Vdy chgn dap an D Cdu 9: T a i ncfi c6 gia tdc t r o n g trifdng g, m o t l^c dorn dao dong dieu hoa vdri b i e n goc nho L a y mdc the nSng d v i trx can b k n g K h i l^c chuyen dong n h a n h d a n theo chieu dUcfng d e n v i t r i c6 dong nSng b a n g the tiSng t h i l i goc a cua l^c bang: A V3 • c "° B D " ° GiSi T a i thdri d i e m t , k h i goc lech l a a , the' n a n g cua He l a : W, = mg/ (1 - cos a ) « mg/.2 sin^ ^ « 2mg/ ^ = mg/a^ K h i dong nhng b k n g the n a n g t a c6: W = 2W, = ^ m g / a ' = m g / a ^ Q\ii Chi t i g t d l thi T S D H , C B M6n V $ t I (1) 57