Hello everybody , I am stuck at this question , 1. The problem statement, all variables and given/known data Two blocks of masses m=1kg and M =2kg are connected by a non-deformed light spring .They are lying on a rough horizontal surface . The coefficient of friction is 0.4 ,What minimun constant force has to be applied in the horizontal direction to the block m , in order to shift the order block M . 2. Relevant equations I came up with work energy conservation theorem F.x = 1/2 kx^2 +f1.x + 1/2mv^2 (where F is external force f1is force of friction on m. and v is velocity of mass m) F-kx-f1=ma1 and when block M is just about to move kx=f2 (here f2 is force of friction on M , its leading me nowhere . Any help?