# Homework Help: Representing two couples by a force F

1. May 1, 2014

### TheRedDevil18

1. The problem statement, all variables and given/known data

Sorry if I posted in the wrong section, this is actually an App Maths question, but anyway

The two shafts are subjected to the
torques (couples) shown.

(a) If you represent the two couples by a force F acting
at the origin O and a couple M, what are F and M?

(b) What is the magnitude of the total moment exerted
by the two couples?

Diagram:

2. Relevant equations

3. The attempt at a solution

I do know what M is, long story but my final answer is 6.05Nm. I just don't get how to solve for F and I am completely stuck, any help ?

2. May 1, 2014

### paisiello2

∑F=ma

Last edited: May 1, 2014
3. May 2, 2014

### BvU

I'm subscribing out of curiosity; could you fill in something under 2. and relate to us the long story ? I take it you added up the two pseudovectors ?

4. May 2, 2014

### TheRedDevil18

Firstly I found the components of the moments by using simple trigonometry. I then summed them up and finally to get the magnitude I squared each component added them and took the square root

5. May 2, 2014

### SammyS

Staff Emeritus
Do you have the dimensions of the cube ?

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6. May 2, 2014

### paisiello2

Dimensions of the cube are irrelevant.

7. May 3, 2014

### TheRedDevil18

No, the dimensions are not given. I think the force is zero because the two couples each have two equal and opposite forces(by definition of a couple) that would cancel. Is that correct ?

8. May 3, 2014

### SammyS

Staff Emeritus
I think you are correct. ... but then I'm the guy who asked about dimensions.

9. May 3, 2014

### paisiello2

I agree the resultant force is zero.