1, let the acceleration of object A be: a, and the angular acceleration of the disk be: ε,

Then it is: ε=a/R (1)

Differential equation of moment of momentum: Jε=(g-a)m R (2)

From (1) and (2):

(J+mR^2)a=mgR^2

A = mgr 2/(j+Mr 2) j is the moment of inertia of the disk: j = m' r 2/2.

Then: a = 2 mg/(m'+2m)

2. From: a = 2mg/(m'+2m), we can get: ε = 2mg/r (m'+2m),

Then it is: θ = ω 0t+ε t 2/2.

θ=εt^2/2=mgt^2/R(m'+2m)，