Help me proving this Kinetic Friction Coefficient

[Calabi_Yau]

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.

 

[nuclear_dog]

Is there any condition given that M >> m . since in that case (1 + m/M) will tend to 1, and your expression will reduce to the required expression. I am also getting the same answer as you got.

 

[tiny-tim]

me too

 

[rude man]

Does 4 make a greater charm than 3?