Q.

A system consists of three masses m1,m2 and m3 connected by a string passing over a pulley P. The mass m1 hangs freely and m2 and m3 are on a rough horizontal table (the coefficient of friction = μ). The pulley is frictionless and of negligible mass. The downward acceleration of mass m1 is

(Assume m1=m2=m3=m)                                          [2014]

1 g(1-gμ)9  
2 2gμ3  
3 g(1-2μ)3  
4 g(1-2μ)2  

Ans.

(3)

Force of friction on mass m2=μm2g

Force of friction on mass m3=μm3g

Let a be the common acceleration of the system.

  a=m1g-μm2g-μm3gm1+m2+m3

Here,  m1=m2=m3=m

  a=mg-μmg-μmgm+m+m

=mg-2μmg3m

=g(1-2μ)3