Friction
Since some of the initial kinetic energy will go (transform) into some heat, the Elost should be a positive term if it is on the final side, or a negative term if it is on the initial side.
S Energiesinitially = S Energiesfinally .
KEi + PEi = KEf + PEf + Elost
where Elost = + Ffriction*s = + mFcs .