How to find the Coefficent of friction w/o the m?

boandrespect already showed you this quantitatively; the qualitative idea is that the frictional force is proportional to the normal force which is proportional to the m, so the acceleration on the object due to the frictional force will always be the same no matter what the m - when you make your calculations, you'll be dividing by and then multiplying by a m, so it's as if you didn't have anything to do with the m in the first place. If it makes you feel better, you can think up a number for the m (preferably 1 kg, for convenience) and you'll see that the mass doesn't really matter. You can then find acceleration of the puck with your kinematics equations and the frictional force with F=ma, and then compare with the normal force (again using the mass you imagined :]) to get �.