Interesting exercise: Torque, radiation, momentum and equilibrium

[LCSphysicist]

Homework Statement

Print below

Relevant Equations

.

t is Torque
I is the inertia moment
P is the power
c is the constant light speed
r is the spot distance to the fiber
p is the torsional constant
theta is what we want
In the equilibrium $$t = 0$$

$$ F\Delta T = \frac{E}{c} = \frac{P\Delta T}{c} => *F* = \frac{P}{c} (1) $$
This will be the "model" equation to the force
$$ t = rF - p\Theta = 0 $$
But, as 0,4 photons are absorbed and 0,6 has their vector momentum on the contrary
$$ (0,4\frac{P}{c} + 2*0,6\frac{P}{c}) = F $$
$$\frac{1.6rP}{pc} = \Theta $$

Is this right?
"we can find p with I and m, but if this above is right, i though the rest is straightforward

 

[haruspex]

Looks good.