Giai K h i dong n a n g v a t h e n a n g bang nhau, t a c6: Wd = — mv^ = — k x ^ 2 Ccf n a n g cua he: W = —mv^+ —kx^ = mv^ = —kA^ 2 ,2 = li^A^=lco^A^=>A = ^ V = ^ V = V ^ ( c m ) m CO 10 ^ ^ Vdy chqn dap an D Cdu 49: K h i n o i ve t i a h o n g ngoai, p h d t bieu nao sau day l a sai? A T i a h o n g ngoai c6 t a n so nho hofn t a n so cua a n h sang t i m B T i a h o n g ngoai c6 b a n chat l a song dien tCr C Cac v a t d n h i $ t t r e n 2000''C chi p h a t r a t i a h o n g ngoai D Tac d u n g n o i b a t cua t i a h o n g ngoai l a tac dung n h i e t Giai Cac v a t d n h i e t t r e n 2000°C c6 t h e p h a t r a t i a h o n g ngoai, t i a tuf ngoai, a n h sang t r o n g t h a y Vdy dap an C la sai Cdu 50: D o i vdfi nguyen tuf h i d r o , k h i electron chuyen tCr quy dao M ve quy dao K t h i nguyen tijf p h a t r a p h o t o n c6 budrc song 0,1026nm L a y h = 6,625.10-^'J.s, e = 1,6.10-i'C va c = S l o W s N a n g lifong cua p h o t o n n a y bang: A 12,1 eV B 121 eV C 11,2 eV D 1,21 eV Gi^i N a n g lUcfng cua p h o t o n : s = J ^ = ^ - ^ ^ ^ - ^ ^ " ^ - ^ ^ ^ ^ , - J = 12,leV X 0,1026.10-" Vdy chgn dap an A Cdu 51: M o m en quan t i n h cua mot vat r a n doi vdri mot true quay co dinh A phu thuoc vao momen cua ngoai l\ic gay r a chuyen dong quay cua v a t r a n B C O gia t r i dtfcfng hoac a m t u y thuoc vao chieu quay cua v a t r ^ n C k h o n g phu thuoc vao sir p h a n bo k h o i Itfcfng cua v a t rSn d o i vdri true quay D dac t r i f t i g cho muTc qudn t i n h cua v a t r ^ n t r o n g chuyen dong quay quanh t r u e ay 48 • GiSi Chi tigt thi T S S H , C D M6n V$t If