1. The problem statement, all variables and given/known data Two bars of masses m1 and m2 connected by a non-deformed light spring rest on a horizontal plane. The coefficient of friction between the bars and the surface is equal to k. What minimum constant force has to be applied in the horizontal direction to the bar of mass m1 in order to shift the other bar? 2. Relevant equations Friction = mgk 3. The attempt at a solution Since the spring transfers the force applied to m1, I assumed I could treat the two masses as a single mass m1+m2. Thus the minimum force required is (m1+m2)gk. This is the wrong answer- but I don't know what I did wrong. Any suggestions? Thanks.