52. A simple Atwood's machine remains motionless when equal masses M are placed on each end of the chord. When a small mass m is added to one side, the masses have an acceleration a. What is M ? You may neglect friction and the mass of the cord and pulley.
(A) 2am(g−a)
(B) a2m(g−a)
(C) a2m(g+a)
(D) 2am(g+a)