Two identical blocks, each of mass \(m\), are connected by an ideal spring and rest on a frictionless horizontal floor. A constant horizontal force of magnitude \(F\) is applied to the right block, pulling it toward the right. At a particular instant, the left and right blocks move to the right with speeds \(v_1\) and \(v_2\), respectively, where \(v_2 > v_1\). Which of the following expressions represents the instantaneous rate of change of the internal energy of the two-block-spring system?