Mechanical Energy Changes in Perfectly Inelastic Collisions

Suppose a block of mass m sub 1 traveling at speed vsub 1 makes a one-dimensional perfectly inelastic collision with another block of mass m sub 2. What else does one need to know to calculate the fraction of the mechanical energy that is dissipated in the collision One needs to know the velocity vsub 2 of the other block defining its sign to be positive if it is in the same direction of travel as the first block, and negative otherwise. That makes sense because there is nothing special about the first block compared to the second one the energy loss must be the same if we interchange subscripts 1 and 2.