1. The problem statement, all variables and given/known data Inside a mass M box, over a horizontal floor, there are a massless spring of elastic constant k, fixed to a body of mass m. That body is trapped to a wire in the bottom of the box. After the wire breaks the box will jump with which deformation b of the spring? 2. Relevant equations F=m.g F=k.b 3. The attempt at a solution I know the answer is that below but i just can't think how would I get to it. b > (M + 2m)g/k.