14 A \(\pounds 2\) coin has a diameter of 28 mm and a mass of 12 grams.
A uniform rod \(A B\) of length 160 mm and a fixed load of mass \(m\) grams are used to check that a \(\pounds 2\) coin has the correct mass.
The rod rests with its midpoint on a support.
A \(\pounds 2\) coin is placed face down on the rod with part of its curved edge directly above \(A\).
The fixed load is hung by a light inextensible string from a point directly below the other end of the rod at \(B\), as shown in the diagram.
\includegraphics[max width=\textwidth, alt={}, center]{ad6590e8-6673-45ca-bef3-a14716978827-22_195_766_854_639}
14
- Given that the rod is horizontal and rests in equilibrium, find \(m\).
14 - State an assumption you have made about the \(\pounds 2\) coin to answer part (a).