Question

A disk with a mass is 3kg. diameter is 20cm, rotating about its symmetry axis

a) compute the rational inertia of the disk

b)three 1 kg masses are placed at the edge of this disk, each seperated by 120 degrees. what is the total rotaional inerteria?

Answer 1

Mass of the disk = M = 3 kg

Diameter of the disk = D = 20 cm = 0.2 m

Radius of the disk = R = D/2 = 0.2/2 m = 0.1 m

Rotational inertia of the disk = I₀

I₀ = 0.015 kg.m²

Number of objects placed on the edge of the disk = n = 3

Mass of each object placed on the edge of the disk = m = 1 kg

The objects are placed at the edge of the disk therefore they are at a distance equal to the radius from the center.

Total rotational inertia of the system = I

I = 0.045 kg.m²

a) Rotational inertia of the disk = 0.015 kg.m²

b) Total rotational inertia of the system = 0.045 kg.m²