A point mass $m$ rests on a long block of mass $2m$, which sits on a horizontal floor. The coefficient of friction between the mass and the block is $\mu$; between the block and the floor it is $\mu/4$. (Static and kinetic values are equal at each interface.) An impulse delivers horizontal momentum $p$ to the point mass. After all motion has ceased, what fraction of the initial kinetic energy has been dissipated by friction between the block and the floor? Assume the mass does not fall off the block.