Figure shows two pulley arrangements for lifting a mass m. In (a) the mass is lifted by attaching a mass 2m while in (b) the mass is lifted by pulling the other end with a downward force F= 2mg, If fa & fb are the accelerations of the two masses then (Assume string is mass less and pulley is ideal)
(A) fa = fb
(B) fa = fb/2
(C) fa = fb/3
(D) fa = 2fb