加速度a =6合力=拉纳谈力T - f =ma=12(N)指茄纯所以 f = 8(N)撤唯咐去外力后 a‘ = 4t = 24/4 = 6 (s)后物体即静止位移S = 6 x 1/2 x (0+24) = 72 (m)