A uniform solid disk of mass \(M\) and radius \(R\) is mounted on a frictionless horizontal axle that passes through its center. A light string is wrapped around the outer edge of the disk, and a constant force of magnitude \(F\) is applied to the end of the string, as shown in the figure. The rotational inertia of a solid disk about its center is \(I = \dfrac{1}{2}MR^2\). Which of the following is a correct expression for the magnitude of the angular acceleration of the disk?