Finding angular acceleration from torque

[mohabitar]

We have to analyze this video:

Givens:

1) An applied net torque due to the wind on the windmill is equal to 1500 N*m.

2) Each (of the 3) propeller props weighs approximately 45 Kg and has a Moment of Inertial equal to about 65% of that of a rod of the same mass being spun about its end.

3) This torque is applied for approximately 45 seconds before the explosion, prior to which the windmill was at rest.

Question: What was the angular acceleration caused by the torque?

So here's my attempt at it: T=Ia (a is alpha) T=ML^2/3 * a * .65 (due to the whole 65% thing. Actually not sure if I should put 3*M for each propeller)

And so this is where I get stuck. I'm not given L, so I'm not sure how to work around this. I could also use T=1/2*MR^2*a, but then I don't know R.

 

[Chi Meson]

You are correct in that you would need to know the length of the blades, which is also the radius of the circle. The radius of motion is crucial for moment of inertia. It's more than crucial, it's "crucial squared." I watched the video, and there is no reasonable way to estimate the size of this turbine since there is nothing in the scene to compare it to. The best thing to do is keep the "L" in as a variable and find the answer in terms of a "coefficient times L"
such as "3.25 L^2." (But I made that number up).

And you can multiply the I of each propeller x 3 for the net I of the turbine, and I think that the .65 is correctly applied, if I am understanding the question correctly.