对物体：ng-T=ma ① 对滑轮：TR=MR2·&=MRa ② ①②→a=2mg/(2m+M) .·a=const. v=at =2mgt/(2m+M) Note: 绳中张力T<mg 对物体： mg −T = ma ① 对滑轮： TR MR 1 2 MRa ② 2 2 1 =  = ①②→ a = 2mg /(2m + M )  a = const.  v = at = 2mgt /(2m+ M) Note: 绳中张力 T  mg