5 A uniform circular disc has diameter \(A B\), mass \(2 m\) and radius \(a\). A particle of mass \(m\) is attached to the disc at \(B\). The disc is able to rotate about a smooth fixed horizontal axis through \(A\). The axis is tangential to the disc. Show that the moment of inertia of the system about the axis is \(\frac { 13 } { 2 } m a ^ { 2 }\). The disc is held with \(A B\) horizontal and released. Find the angular speed of the system when \(B\) is directly below \(A\). The disc is slightly displaced from the position of equilibrium in which \(B\) is below \(A\). At time \(t\) the angle between \(A B\) and the vertical is \(\theta\). Write down the equation of motion, and find the approximate period of small oscillations about the equilibrium position.