Asked by Shelby

A typical propeller of a turbine used to generate electricity from the wind consists of three blades as in the figure below. Each blade has a length of L = 33 m and a mass of m = 415 kg. The propeller rotates at the rate of 21 rev/min. 120degree angle between blades
a) Convert the angular speed of the propeller to units of rad/s.
(b) Find the moment of inertia of the propeller about the axis of rotation.___J · s2
(c) Find the total kinetic energy of the propeller.______ J
Answered by bobpursley
This is pretty standard question. What is it you do not understand?

For the moment of inertial figure each blade rotating about its end, then multiply by three.

KE=1/2 Itotal*w^2
Answered by Brandy
(A) w = (21rev/min) * (1min/60sec) * (2pi rad/1rev) = 2.2 rad/s

(B)

I = MR^2
I = (415kg)(33m)^2
I = 4.52E5 (I for one propeller)

I for all three propellers = (4.52E5) * 3 = 1.36E6

(C) KE = (1/2) * Iw^2

= (1/2)(4.52E5)(2.2)^2
=1.1E6 J

The book gives solutions for I and KE using one propeller. My thought were to multiply I *3....a little confusing. Thoughts...?

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