Parallel and Perpendicular Axis theorem is considered one the most difficult concept.
35 Questions around this concept.
For the given uniform square lamina ABCD, whose centre is O,

Consider a thin uniform square sheet made of a rigid material. If its side is 'a', mass m and moment of inertia I about one of its diagonals, then :
Consider a uniform square plate of side a and mass m. The moment of inertia of this plate about an axis perpendicular to its plane and passing through one of its corners is
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The moment of inertia of a solid sphere, about an axis parallel to its diameter and at a distance of x from it, is 'I(x)'. Which one of the graphs represents the variation of I(x) with x correctly ?
Two identical spherical balls of mass M and radius R each are stuck on two ends of a rod of length 2R and mass M (see figure) The moment of inertia (MR2) of the system about the axis passing perpendicularly through the centre of the rod is :
From the theorem of the perpendicular axis. If the lamina is in the Y-Z plane
Parallel Axis Theorem-
$I_{b b^{\prime}}=I_{a a^{\prime}}+M h^2$

$b b^{\prime}$ is axis parallel to $a a^{\prime} \& a a^{\prime}$ an axis passing through the centre of mass.
Perpendicular Axis theorem-

$
I_z=I_x+I_y
$
(for a body in XY plane )
Where $I_z=$ moment of inertia about the z axis
$I_x I_y$ :moment of inertia about $\mathrm{x} \& \mathrm{y}$ axis in the plane of body respectively.
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