Answer
Graph (c) and Graph (d) are physically impossible.
Work Step by Step
Graph (a) and graph (b) are both physically possible since the sum of the final kinetic energy of each block is equal to or less than the initial kinetic energy.
Graph (c) is physically impossible because the final kinetic energy of one block is negative on the graph.
Graph (d) is physically impossible because the sum of the final kinetic energy of each block is greater than the initial kinetic energy.
