A bar has a magnetic moment equal to `5xx10^(-5) weberxxm`. It is suspended in a magnetic field which has a magnetic induction (B) equal to `8pixx10^(-4)` tesla. The magnet vibrates with a period of vibration equal to 15 sec. The moment of intertia of the magnet is
A. `22.5 kgxxm^(2)`
B. `11.25xxkgxxm^(2)`
C. `5.62xxkgxxm^(2)`
D. `7.16xx10^(-7)kgm^(2)`