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

  • Thread starter Thread starter Bismuth
  • Start date Start date
  • Tags Tags
    Couple Moments
AI Thread Summary
The discussion revolves around calculating the coordinate direction angles for the resultant couple moment from two forces, F1 and F2. The calculated moments are M1 = 220 lb*ft and M2 = 600 lb*ft, leading to a resultant moment MR of -180(i) + 300(j) + 0(k). The angles derived from this resultant are α = 121 degrees and β = 31 degrees, with confirmation that the couple makes an angle of 121 degrees counterclockwise with the positive x-axis. Despite initial confusion, the calculations are validated, and the angles are reiterated as correct. The conversation emphasizes clarity in understanding the relationship between the angles and the resultant moment.
Bismuth
Messages
5
Reaction score
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 = \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:
Physics news on Phys.org
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:
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'Collision of a bullet on a rod-string system: query'
In this question, I have a question. I am NOT trying to solve it, but it is just a conceptual question. Consider the point on the rod, which connects the string and the rod. My question: just before and after the collision, is ANGULAR momentum CONSERVED about this point? Lets call the point which connects the string and rod as P. Why am I asking this? : it is clear from the scenario that the point of concern, which connects the string and the rod, moves in a circular path due to the string...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top