Line of action from pivot to force should be zero?

[johnnyboy53]

Homework Statement

I am seeing the steps on others who have worked this out and they are taking the pin as the pivot position. I thought a force's line of action that passes the pivot position produces zero torque? So i tried to make the center of mass the pivot position and each calculate each torque with respect to the center of mass, which is the wrong approach. So why can we say that the pin produces a torque when the force of the pin's line of action crosses the pivot position? Shouldn't that produce a torque of zero?

Homework Equations

The Attempt at a Solution

 

[haruspex]

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