4 A uniform circular disc has mass \(m\), radius \(a\) and centre \(C\). The disc is free to rotate in a vertical plane about a fixed horizontal axis passing through a point \(A\) on the disc, where \(C A = \frac { 1 } { 3 } a\).
- Find the moment of inertia of the disc about this axis.
The disc is released from rest with \(C A\) horizontal.
- Find the initial angular acceleration of the disc.
- State the direction of the force acting on the disc at \(A\) immediately after release, and find its magnitude.