- #1

Mikejax

- 7

- 0

**Moments and force couples...confused!**

## Homework Statement

I have attached 2 pdfs: 1 is the problem, the second is the solution. I need help understanding the solution. Diagrams included.

The gist of the problem:

Need to calculate a dimension "a" such that a resultant couple (from 2 force couples) will equal 480 N-m. I understand how they reduce couple AD, but not how they reduce couple CF. They reduce couple cf in their expression Mc + Mf + forcecouple C and F about C.

I understand why they take C and F about C, but why are Mc and Mf added on top this? I am trying to follow the following principle: The moment induced by 2 equal and opposite forces is equal to the moment of the one force about the point of application of the other".

I don't get how adding Mc and Mf on top this works. (I am referring to the first line of math under the diagram of the solution).

I am so confused, it would be so amazing if someone here could clarify this for me.

## Homework Equations

M = M1 + M2## The Attempt at a Solution

see above.