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

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Homework Help Overview

The discussion revolves around determining the coordinate direction angles for the resultant couple moment involving two forces, F1 and F2. The problem is situated within the context of mechanics, specifically dealing with moments and their components in a three-dimensional space.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • The original poster attempts to calculate the resultant couple moment and its coordinate direction angles, expressing confusion about the complexity of the angles involved. They provide their calculations for the moments and express uncertainty about their approach.
  • Some participants question the clarity of the image provided, which is essential for understanding the problem setup.
  • Others suggest that the original poster's calculations may be correct, but they seek clarification on the definitions of the angles alpha and beta in relation to the axes.
  • There is an exploration of various angle combinations that the original poster has tried, indicating a search for the correct interpretation of the angles based on their resultant moment.

Discussion Status

The discussion is ongoing, with participants providing feedback on the original poster's calculations. Some guidance has been offered, suggesting that the calculations may be correct, but there remains a lack of consensus on the correct angles. The original poster continues to seek clarification and validation of their results.

Contextual Notes

Participants note the importance of the image for understanding the problem, which is currently inaccessible. There is also a mention of the potential for misunderstanding the definitions of the angles alpha and beta, which may affect the interpretation of the results.

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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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