Question

A system consists of three masses m1 m2 and m3 connected by a string

Answer 1

Here friction f2 and f3 will oppose the motion and weight (m1g=mg) will support the motion.

So, acceleration of mass m1 is

a=Net Force/Total mass

or,   

a=mg−μmg−μmg/3m          

=mg(1−2μ)/3m         

=g(1−2μ)/3

Answer 2

hope this helps....