A disc of mass m is connected with an ideal spring of spring constant k inside a lift as shown.The lift starts moving with constant acceleration (ai -aj )At the same moment disc starts rolling without sliding on the wall of lift (from rest). If spring is in natural length initially then friction force acting on disc as a function of y is given by: (y is the displacement of the disc with respect to lift)
(A) –ky
(B) 2 /3 (mg + ma – ky)
(C) 1/3 (mg + ma – ky)
(D) mg + ma – 2ky
