a student conducts an experiment in which an object is released from rest and falls to the floor. in the experiment, frictional forces cannot be neglected. the student uses experimental data to create two graphs. figure 1 is a graph of kinetic energy of the object as a function of time. figure 2 is a graph of the object-earth system’s gravitational potential energy as a function of time. how should the student use one or both graphs to determine how much the total mechanical energy changes after 5s ?