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

In summary, to determine the magnitude and coordinate direction angles of the resultant couple moment, you can use the formula MR = \Sigmar x F, where M is the moment, r is the position vector, and F is the force. By breaking down the angled moment into its x and y components, summing them together, and finding the resultant moment, you can determine the angles between the moment axis and the x and y axis. In this case, the angles are \alpha = 121 degrees and \beta = 31 degrees.
  • #1
Bismuth
6
0

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 = [tex]\Sigma[/tex]r 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 [tex]\alpha[/tex] = 121o and [tex]\beta[/tex] = 31.0o

I'm pretty sure I'm over complicating things and making a stupid mistake. Any guidance would be greatly appreciated. Thank you.
 
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  • #2
Your image does not appear.
 
  • #3
PhanthomJay said:
Your image does not appear.

How very computer illiterate of me. Thank you for letting me know!
 
  • #4
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 = [tex]\Sigma[/tex]r 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 [tex]\alpha[/tex] = 121o and [tex]\beta[/tex] = 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!
 
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  • #5
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:

[tex]\alpha[/tex] = 121, [tex]\beta[/tex] = 31
[tex]\alpha[/tex] = 149, [tex]\beta[/tex] = 31
[tex]\alpha[/tex] = 31, [tex]\beta[/tex] = 59
[tex]\alpha[/tex] = 59, [tex]\beta[/tex] = 31

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

What is "Adding Couple Moments"?

"Adding Couple Moments" is a technique used in physics to describe the rotational motion of a system. It involves calculating the total torque, or rotational force, acting on an object and using that to determine its angular acceleration.

How is "Adding Couple Moments" different from regular addition?

While regular addition involves combining two numbers to get a sum, "Adding Couple Moments" involves combining multiple torques acting on an object to determine its overall rotational motion.

Why is "Adding Couple Moments" important?

"Adding Couple Moments" is important in understanding rotational motion and predicting the behavior of objects such as spinning tops, gyroscopes, and wheels. It is also used in engineering and design to ensure stability and balance in structures and machines.

What is the formula for "Adding Couple Moments"?

The formula for "Adding Couple Moments" is Στ = Iα, where Στ represents the total torque, I is the moment of inertia, and α is the angular acceleration.

How do you calculate the total torque in "Adding Couple Moments"?

The total torque is calculated by adding up all the individual torques acting on an object. This can be done by using the equation Στ = F * d * sin(θ), where F is the force applied, d is the distance from the pivot point, and θ is the angle between the force and the lever arm.

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