4 A uniform lamina ABDE is in the shape of an equilateral triangle ABC of side 12 cm from which an equilateral triangle of side 6 cm has been removed from corner \(C\). The lamina is situated on coordinate axes as shown in Fig. 4.
\begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{fa99d9e6-e174-42dd-ac92-7b7d112c08be-4_501_753_406_646}
\captionsetup{labelformat=empty}
\caption{Fig. 4}
\end{figure}
- Explain why angle \(\mathrm { BDA } = 90 ^ { \circ }\).
- Find the coordinates of the centre of mass of the lamina ABDE .
The lamina ABDE is now freely suspended from D and hangs in equilibrium.
- Calculate the angle DE makes with the downward vertical.