Let say we have a horizontal mass-spring system oscillates without friction on a smooth surface. One side of the spring is attached / fixed to a wall. The other is where the mass is attached to. Let say we choose our system to be the mass and the spring (negligible mass), so our free body diagram for the system that we have chosen consists of the following forces: Normal force on the mass. (A) Weight on the mass. (B) Spring force on the mass (C). Same force (D) will be acting on the spring according to Newton's third law. Another force (E) is exerted on the spring by the wall. Question: What is the work done by force E on the spring? Explain.