A bar magnet has a magnetic moment equal to $5 \times 10^{-5}\,\text{Wb\,m}$. It is suspended in a magnetic field which has a magnetic induction $B = 8\pi \times 10^{-4}\,\text{T}$. The magnet vibrates with a period of vibration equal to $15\,\text{s}$. The moment of inertia of magnet is