Block A of mass 2m,B and C each of mass m are in equilibrium at rest as shown in figure.Assume the spring balance,pulley and string to be ideal.Now,an additional force mg is applied on block C in downward direction .Find the new reading of the spring balance
(a) 5/2 mg (b) 5/3 mg (c) 5/4 mg (d) None of these

In the beginning the system is in equilibrium.   When additional force mg acts on mass of block C then,        ma=2mg-T-----1and       ma = T-mg----2from eqn 1 and 2 we get,                  2ma = mgor                       a = g/2 Now eqn of motion for block A is given by,        2ma =T-2mgPutting the value of a in above eqn, we get,         T =2ma+2mg=2m×g/2 +2mg =3mg.Therefore answer D none of these  is correct.    

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