The situation is shown :- All surfaces are frictionless. I am trying to find the max extension of the spring as the force is applied. Spring is massless. F=ma I tried drawing FBDs for block A and B:- F-kx=Ma(from fbd of A) kx=ma(from fbd of B) , we get x=Fm/k(M+m) Is this correct?? Also can anyone explain how to visualize when spring if stretched from both sides? How do you then apply Hooke's law?