# Physics problem! Finding the moment of inertia of a hexagon.?

The six particles (of negligible size) in the figure opposite are connected together by rigid rods of negligible mass. The system forms a perfect hexagon of side 2 m, and the particles have a mass of 1 kg each.

a) Calculate the moment of inertia (no unit needed) of the system about an axis perpendicular to the plane and passing through the centre of mass of the system.

b) Calculate the moment of inertia (no unit needed) of the system about an axis parallel to the one in (a), but passing through one of the masses.

### 5 Answers

- Steve4PhysicsLv 72 years agoFavorite Answer
a) If you mark the centre and join each mass to the centre, you see you have 6 equilateral triangles. Distance of each mass to axis (centre) r = 2m.

Moment of inertia of each mass = mr² = 1 * 2² = 4 kgm²

Total moment of inertia I = 6 x 4 = 24 kgm²

b) Total mass M = 6kg

Axis displaced d=2m. Using parallel axis theorem, moment of inertia through a mass = I + Md² = 24 + 6*2² = 48 kgm²

- Anonymous2 years ago
it's 60 degrees at 420 .

- Anonymous2 years ago
The hexagon isn't moving because plane, 2D objects don't exist in real life.

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