# Finding the resultant couple moment

1. Jan 26, 2012

### theBEAST

1. The problem statement, all variables and given/known data
I attached the question as a picture to this thread

2. Relevant equations
M=Fd

3. The attempt at a solution
I was taught that the moment produced by two equal but opposite forces is the magnitude of one force multiplied by the distance between the two forces.

I used Pythagoras to solve for the distances between each of the couples and found sqrt32 and sqrt8 to be these distances.

Thus
M1= 150*sqrt32
M2=200*sqrt8

and the resultant moment
=M1-M2
=283Nm [clockwise]

This is not the answer, the method the answer key used was breaking up the couples into x and y. I don't understand why my method does not work as well.

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2. Jan 26, 2012

### tiny-tim

hi theBEAST!
nooo

√32 and √8 are the distances between the points of application of these forces

the couple uses the distance between the lines of application of the forces