1. The problem statement, all variables and given/known data Quick conceptual questions: Is springs are considered a non-conservative force why is the mechanical energy conserved when a moving object compresses the spring? 2. Relevant equations 3. The attempt at a solution This isn't a homework question or anything but I working on a problem that involves a spring and the problem says that a mass horizontally attached to a spring is moving compressed by a bullet being shot into the mass (wood) and that the mechanical energy is conserved during the compression of the spring. Confused.