A block on a horizontal floor is initially either stationary, sliding in the positive direction of an x axis or sliding in the negative direction of that axis. The block then explodes into two pieces that slide along the x axis. If the two pieces are an isolated system, determine which of the graphs below represent impossible situations.

A block on a horizontal floor is initially either stationary, sliding in the positive direction of an x axis or sliding in the negative direction of that axis. The block then explodes into two pieces that slide along the x axis. If the two pieces are an isolated system, determine which of the graphs below represent impossible situations.