4.
\begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{60b9db45-b48e-40a1-bd22-909e11877bc3-3_275_842_194_408}
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\caption{Fig. 2}
\end{figure}
Figure 2 shows a uniform plank \(A B\) of mass 50 kg and length 5 m which overhangs a river by 2 m . When a boy of mass 20 kg stands at \(A\), his sister can walk to within 0.3 m of \(B\), at which point the plank is in limiting equilibrium.
- What is the mass of the girl?
- Find the smallest extra weight which must be placed at \(A\) to enable the girl to walk right to the end \(B\).
- How have you used the fact that the plank is uniform?