What are the coordinate direction angles for the resultant couple moment?

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SUMMARY

The discussion focuses on calculating the coordinate direction angles for the resultant couple moment generated by two forces, F1 = 110 lb and F2 = 300 lb. The calculated resultant couple moment is MR = -180(i) + 300(j) + 0(k), leading to angles α = 121° and β = 31°. The user confirmed that the resultant couple makes an angle of 121° counterclockwise with the positive x-axis, affirming the correctness of their calculations. The angles α and β represent the angles between the moment axis and the x and y axes, respectively.

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Homework Statement



[PLAIN]http://img25.imageshack.us/img25/5139/physicsproblem.jpg

If F1 = 110 lb and F2 = 300 lb, determine the magnitude and coordinate direction angles of the resultant couple moment.

Homework Equations



MR = \Sigmar x F, M = Fd

The Attempt at a Solution



Unfortunately, the couple on the angle is too much for my tiny brain to tolerate. I have found the moments to be:
Couple moment of the forces on image M250 = 500 lb*ft
M1 = 220 lb*ft (i)
M2 = 600 lb*ft (j)

I tried to further break up the angled moment M250 into its x and y components based on the hypotenuse it lies perpendicular to of the 3-4-5 triangle within the box, which gave me M = -400(i) - 300(j) + 0(k). Summing all the moments together gives me MR = -180(i) + 300(j) + 0(k), from which I get \alpha = 121o and \beta = 31.0o

I'm pretty sure I'm over complicating things and making a stupid mistake. Any guidance would be greatly appreciated. Thank you.
 
Last edited by a moderator:
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Your image does not appear.
 
PhanthomJay said:
Your image does not appear.

How very computer illiterate of me. Thank you for letting me know!
 
Bismuth said:

Homework Statement



[PLAIN]http://img25.imageshack.us/img25/5139/physicsproblem.jpg

If F1 = 110 lb and F2 = 300 lb, determine the magnitude and coordinate direction angles of the resultant couple moment.

Homework Equations



MR = \Sigmar x F, M = Fd

The Attempt at a Solution



Unfortunately, the couple on the angle is too much for my tiny brain to tolerate. I have found the moments to be:
Couple moment of the forces on image M250 = 500 lb*ft
M1 = 220 lb*ft (i)
M2 = 600 lb*ft (j)

I tried to further break up the angled moment M250 into its x and y components based on the hypotenuse it lies perpendicular to of the 3-4-5 triangle within the box, which gave me M = -400(i) - 300(j) + 0(k). Summing all the moments together gives me MR = -180(i) + 300(j) + 0(k), from which I get \alpha = 121o and \beta = 31.0o

I'm pretty sure I'm over complicating things and making a stupid mistake. Any guidance would be greatly appreciated. Thank you.
You didn't overcomplicate it at all, you did it perfectly! Note that the resultant couple makes an angle of 121 degrees ccw with the positive x axis, which I assume is your beta angle. Nice work!
 
Last edited by a moderator:
PhanthomJay said:
You didn't overcomplicate it at all, you did it perfectly! Note that the resultant couple makes an angle of 121 degrees ccw with the positive x axis, which I assume is your beta angle. Nice work!

It wants alpha as the angle between the moment axis and the x axis, and beta as the angle between the moment axis and the y axis. I have tried inputting the following:

\alpha = 121, \beta = 31
\alpha = 149, \beta = 31
\alpha = 31, \beta = 59
\alpha = 59, \beta = 31

With no success. Given the resultant moment I found, I believe it should be \alpha = 121, \beta = 31. Thanks for your help!
 
Last edited:

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