Determine the rotational inertia of the construction about an axis perpendicular to the picture and passing through point b.

m* 8.0 kg*m²

Explanation:

Rotational inertia of a set of discrete masses (considered point masses), regarding an axis passing through a given point, is just the sum of the products of each mass times the distance to the point of interest.

In the attached picture, neglecting the masses of the rods joining the masses, and taking into account that all masses are equal each other, being  equal to m kg, we can write the following equation:

I = m₁*r₁² + m₂*r₂² + m₃*r₃² + m₄*r₄²,  

⇒ I = m kg*0 +m kg*2 m² +m kg*2m² + mkg*4m²

⇒ I = m*8 kg*m²