1 A uniform semicircular lamina has diameter \(A B\) of length 0.8 m .
- Find the distance of the centre of mass of the lamina from \(A B\).
The lamina rests in a vertical plane, with the point \(B\) of the lamina in contact with a rough horizontal surface and with \(A\) vertically above \(B\). Equilibrium is maintained by a force of magnitude 6 N in the plane of the lamina, applied to the lamina at \(A\) and acting at an angle of \(20 ^ { \circ }\) below the horizontal.
- Calculate the mass of the lamina.