Question

moment of inertia of a bar magnet of mass m length l breath b is l.then moment of inertia of another bar magnet of mass 2m Length 2l breath 2b would be

Answer 1

moment of inertia of a magnet of mass m, length l, breadth b along an axis passing through its centre is
I = m(l^2 + b^2) / 12 ..... eq. 1

Then, moment of inertia of another bar magnet of mass 2m, length 2l and breadth 2b is
I' = 2m[ (2l) ^2 + (2b)^2 ] / 12
= 2m ( 4l^2 + 4b^2 ) / 12
= 8m ( l^2 + b^2 ) / 12
= 8 I...... from eq. 1