Two blocks of masses \(m\) and \(2m\) are placed on a horizontal surface where the coefficient of kinetic friction between each block and the surface is \(\mu_k\). A compressed ideal spring between the blocks is released at time \(t = 0\), causing the block of mass \(m\) to move to the left with initial speed \(2v_0\) and the block of mass \(2m\) to move to the right with initial speed \(v_0\). The spring detaches immediately after release, and the blocks slide along the surface until both come to rest. Defining the positive direction to the right, which of the following best describes the shape of the graph of the velocity of the center of mass, \(v_{cm}\), of the two-block system as a function of time \(t\)?