Rotating Anemometer?

Question

An anemometer for measuring wind speed consists of four metal cups, each of mass m = 105 g, mounted on the ends of four essentially massless rods of length R= 0.32 m. The rods are at right angles to each other and the structure rigidly rotates at f = 12 rev/s. Treat the cups as point masses.

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a) What is the moment of inertia of the anemometer about the axis of rotation?

I = g m2

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b) What is the angular momentum of the anemometer about the rotation axis?

L = g m2/s

Answer 1

If the cups are considered to be point masses,

I = 4(105 g)(0.32 m)^2

I = 43.008 g∙m^2 ≈ 43 g∙m^2 ≈ 0.043 kg∙m^2

L = Iω

L = (43 g∙m^2)(12 rev/s)(2π rad/rev)

L ≈ 3,242.7 g∙m^2/s ≈ 3.24 kg∙m^2/s