The answer is A. X rays or it can be visible light but mostly A.
The disk has a moment of inertia of 1/2 M R^2
and dw/dt = T /I but T = F* R so dw/dt = F*R/I = F*R/( 1/2 M R^2) = 2 F/(MR) Now v = wR so dv/dt = 2 F / M
For the individual to rush at g/4 then the force performing on the wheel must be 3mg/4 ( where m = 90 kg) so g/4 = 2 * 3mg / 4M 1 = 2*3 m / M M = 6 * 90 = 540kg
And tension must be 3/4 of the weight of the person = 3mg/4 = 405 N
Well, the lines of workings are cut off in the middle, and there's no 2nd image.
But I think it must have to do with the "cos" terms at the right end of the picture.
I'm guessing now, because the part I'm interested in would be just past the edge, where we can't see it.
I <em>think</em> that the first line says "cos(some angle)", and at the same place in the second line it says "cos(180 - the same angle)".
If that's what it says, then that's your answer, because cos(anything) is equal to the <em>negative</em> of cos(180 - the same thing).
That's the best I can do for you just now. Honestly, I don't see the connection yet between the question Dave is working on and the two lines I see in the picture.