A student attaches a block to a vertical spring of unknown spring constant k0 so that the block-spring system will oscillate if the block-spring system is released from rest at a vertical position that is not the system’s equilibrium position. The student varies the object’s mass and uses a stopwatch to determine the time it takes the object to make one oscillation. The student creates the graph that is shown. The slope of the line of best fit is equal to which of the following quantities?