Determine the rotational inertia of the four balls shown in

Determine the rotational inertia of the four balls shown in Figure P8.28 about an axis perpendicular to the paper and passing through point A. The mass of each ball is m. Ignore the mass of the rods to which the balls are attached.

Solution

MOMENT OF INERTIA OF MASS M at a distance R from the axis is MR²

So for the figure the total rotational inertia is m x 1² + m x 1² + m x 1² + m x 1² = 4 m ans