Moderate -0.3 This is a straightforward moments problem requiring equilibrium about the pivot. Students must identify the pivot position (2m from A), calculate moments for three known masses, and solve a simple linear equation for the unknown distance. It's slightly easier than average as it's a standard mechanics exercise with clear setup and routine calculation, though the multiple objects require careful bookkeeping.
The diagram shows a uniform plank \(AB\) of length 4 m supported in horizontal equilibrium by means of a central pivot. On the plank there are three objects of masses 8 kg, 2 kg and 15 kg placed in positions \(C\), \(D\) and \(E\) respectively. The distance \(AC\) is \(0 \cdot 6\) m and the distance \(AE\) is \(2 \cdot 8\) m.
\includegraphics{figure_3}
Find the distance \(AD\). [4]
The diagram shows a uniform plank $AB$ of length 4 m supported in horizontal equilibrium by means of a central pivot. On the plank there are three objects of masses 8 kg, 2 kg and 15 kg placed in positions $C$, $D$ and $E$ respectively. The distance $AC$ is $0 \cdot 6$ m and the distance $AE$ is $2 \cdot 8$ m.
\includegraphics{figure_3}
Find the distance $AD$. [4]
\hfill \mbox{\textit{WJEC Unit 4 2018 Q6 [4]}}