A disk of radius $R$ rotates about an axis passing through its center and perpendicular to the plane of the disk. The initial angular speed $\omega_i$ is positive, and the disk is given a constant, negative angular acceleration $-\alpha_0$. Which of the following expressions correctly represents the magnitude of the net linear acceleration for a point located at the edge of the disk?
$R\alpha_0$
$R(\omega_i - \alpha_0t)^2$
$R\sqrt{(\omega_i - \alpha_0t)^2 - \alpha_0^2}$
$R\sqrt{(\omega_i - \alpha_0t)^2 + \alpha_0^2}$