This is my first time posting, but I've done quite a bit of reading around on here, and I admire your guys' intuition/skills for this stuff. Most of you appear to have a real knack for conceptualizing these problems, and I'm jealous ;). 1. The problem statement, all variables and given/known data Two identical blocks, A and B, on a frictionless surface are connected by a spring of negligible mass. The spring is initially unstretched. During the interval from t1 to t2, block A is pushed through a distance dA by a hand exerting a force of magnitude FA, as shown. Block B is held in place by a wall. The wall exerts a force on block B that varies with time but is always directed to the left. Write an expression for the net external work done on system ABS by external forces in terms of given quantities (ie. FA, dA, and/or t2). Explain. 2. Relevant equations Work = Force * displacement 3. The attempt at a solution The diagram shows block B resting against a wall, and block A being moved toward B, compressing the spring and moving displacement dA. Block B has zero work done on it (because it experiences no displacement), and block A has work FA*dA. So I know that the net work will have at least that component to it. My question is, do we account for the force of the wall being exerted on block B when we're describing total work on the system? My reasoning is that because the spring experiences compression that wouldn't otherwise occur without the wall, there appears to be a transfer of energy that occurs (that's stored in potential energy of the spring). This is obviously flawed logic though, because the only parts of the system that are experiencing displacement are the parts being directly influenced by the hand, and therefore they must be the only parts of the system with work being performed on them. Could I get some help straightening this out? Thanks!