1. The problem statement, all variables and given/known data A system of two blocks (each of mass M) are connected by a spring with spring constant k. The system is shoved to the left against a wall and the spring is compressed a distance D. The block(s) are then released. Determine the period of oscillation for the system when the left-hand block is no longer in contact with the wall. 2. Relevant equations T=2π√m/k 3. The attempt at a solution So my inclination is to say that T=2π√M/k since I assumed we could consider the oscillation of one individual block to be the same as the other. However, I have the solutions provided by the College Board and they indicate that the mass should be 1/2M resulting in T=2π√M/2k. Can someone explain why the mass is halved?