ac=ag”+acB”+acB aravxlol as”=ac1=o7 3 B ac cos60=ap"sin30+dce" (3分) 号o7(4分) 八、(12分)解: FBy D(1分) (1分) B B ig ac =ac+acy=ac"+ac mdcs Fas mdcy =FBy-mg, =-0-01.0 2 -mfa-FwZ 1 do =-dd'=-al 2 38 求得:a= a6=-子8,=0,R-484分) 1 M F 118 (1分) ∑F=0,Fa-Fa=0 FAs =FBr =0 ∑E=0,F-Fs-mg=0,{F=F+mg=mg (3分) 4 ∑,-0+e分+M=-0M=-f-sg (4分) 共4页第1页(3 分) 2 2 2 2 1 3 1 3 n n t C B CB CB n B BD n CB BC a l l a l l = + + = = = = a a a a cos60 sin 30 n n C B CB a a a = + 3 2 3 C a l = (4 分) 八、(12 分)解: (1 分) (1 分) 1 2 12 2 Cx Bx Cy By By ma F ma F mg l ml F = = − = , 2 0 2 2 n t C Cx Cy C C n BD Cx C t Cy C l a a l a a = + = + = − = = = − = − a a a a a 求得: 3 3 1 , , 0, 2 4 4 Cy Bx By g a g F F mg l = = − = = (4 分) (1 分) 0, 0 0, 0 0, 0 2 x Ax Bx y Ay By A By A F F F F F F mg l M F l mg M = − = = − − = = + + = , 0 5 4 3 2 4 Ax Bx Ay By A By F F F F mg mg l M F l mg mgl = = = + = = − − = − (3 分) (3)根据动能定理: 1 1 2 0 2 2 B J mgl − = , 1 2 3 B J ml = ,故 3g l = (4 分) 共 4 页第 1 页