A bar magnet has a magnetic moment equal to \(5 \times 10^{-5}\,\text{Wb}\cdot\text{m}\). It is suspended in a magnetising field equal to \(8\pi \times 10^{-4}\,\text{A}\cdot\text{m}^{-1}\). The magnet vibrates with a period \(15\,\text{s}\). The moment of inertia of the magnet is: