A yo-yo of total mass \(M\) consists of two uniform solid disks, each of radius \(R\), joined by a central cylindrical axle of radius \(r\) and negligible mass. The rotational inertia of the yo-yo about its central axis of symmetry is \(I = \dfrac{1}{2}MR^2\). A light, inextensible string is wound around the axle, and its upper end is held stationary. The yo-yo is released from rest and falls vertically as the string unwinds without slipping. Which of the following expressions correctly gives the magnitude of the downward linear acceleration \(a\) of the yo-yo and the tension \(T\) in the string during its descent?