Consider the system: A block of mass M is placed on a level table and connected to a mass m by a light string running through a pulley. If mass m is released, it will start to fall and the wooden block will be pulled across the table. Prove that the kinetic friction coefficient can be given by the expression: μ = m/M - a/g I have tried, but could only get this expression: μ= [mg - (M+m)a]/Mg . I can't get to the one outlined in the question. What am I missing? Thanks in advance.