Where I am going wrong in summing moments for this diagram?

[Benjamin_harsh]

Homework Statement

Where I am doing wrong in summing moments for this diagram?

Relevant Equations

$\sum M_{A} = F.(d+d` )-F(d+d` )-F.d$

$\sum M_{A} = F.(d+d` )-F(d+d` )-F.d$

I am getting negative answer. Where I am doing wrong in summing moments for this diagram?

 

[Chestermiller]

If you are summing moments about A, what are the three moment arms equal to?

 

[Benjamin_harsh]

what are the three moment arms equal to?

I think three moment arms nothing but summing moments.

 

[haruspex]

This is a repost of https://www.physicsforums.com/threa...the-force-acting-at-a-in-this-diagram.972491/, but with a better explanation of the question.

 

[haruspex]

First, why are you now showing a force -F at A, which did not appear in the previous version of this thread? Is it something you forgot to mention before or did you invent it yourself? It is curious since the result is not equilibrium.

Secondly, you still don't seem to understand moment arms. The moment arm for the -F at A is the distance from point A to the line you have drawn to represent the force. How far is that? What moment does this force exert about A?

 

[Chestermiller]

I think three moment arms nothing but summing moments.

What does this even mean?