Varrying load distance applies a two equal forces on two roller

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Discussion Overview

The discussion revolves around a homework problem involving the calculation of moments and forces acting on a system of rollers. Participants explore the relationships between various points and forces, specifically focusing on summing moments about different points to determine unknown values.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant suggests summing moments from points A, B, and L about point C, expressing uncertainty about the relationships between these points.
  • Another participant agrees with the approach of summing moments about C, noting that the sum of torques must be zero due to zero angular acceleration.
  • A participant reports calculating a value of b as 27 after summing moments about C.
  • There is a correction regarding the direction of the force at point C, with a participant realizing that the pawl can rotate freely, affecting the analysis.
  • A later post indicates that the equation for b changes when summing moments about point H, leading to a new calculated value of 29.
  • One participant requests detailed calculations to confirm the new value of b.
  • Another participant asserts that the current answer is incorrect and prompts a reevaluation.

Areas of Agreement / Disagreement

Participants express differing views on the correctness of the calculated values for b, with some calculations leading to different results. The discussion remains unresolved as participants continue to challenge and refine their approaches.

Contextual Notes

There are limitations regarding the assumptions made about the forces and their directions, particularly concerning the pawl's behavior and its impact on the calculations. The discussion also reflects dependencies on the specific definitions and relationships between the points in the problem.

GarrettKoep
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Homework Statement



http://img198.imageshack.us/img198/374/20856431.jpg

Homework Equations


Moment = R cross F
Couple moments?

The Attempt at a Solution



I think I have to sum the moments from A, B and L all about C but I am not sure about the relationships between them.
 
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Hi GarrettKoep! :smile:
GarrettKoep said:
I think I have to sum the moments from A, B and L all about C but I am not sure about the relationships between them.

Yes, that's right …

you know the directions of the forces at A B and L, but you have no idea which direction the force is at C, so the only sensible thing is to take moments about C. :wink:

And since the angular acceleration is (obviously!) zero, that means that the sum of the torques (moments) must be zero.

What do you get? :smile:​
 
After summing the moments about C I calculated that b=27
 
Hi GarrettKoep! :smile:
GarrettKoep said:
After summing the moments about C I calculated that b=27

(How did you get that? Anyway …)

erm :redface: … when I said "you have no idea which direction the force is at C", I thought that the "pawl" was rigidly fixed to the rest of the body.

But now that I've looked at the picture more carefully :rolleyes:, I realize that the pawl is loose … it can rotate freely at that unnamed point 8" up … let's call that point H.

And since the pawl isn't rotating, that means that the force at C must balance the force at H.

So we know the direction of both the forces at C and at H.

And the rigid body is supported by forces at A B L and H.

Use that information to find the direction and magnitude of the force at H, and then use moments to find b.

Sorry I missed that point earlier. :redface:​
 
Okay, so if you calculated the sum of the moments about H the equation for b would change from (b-7)*L to (b-9)*L and they others would stay the same ( Fab *20). In conclusion, b would then be equal to 29.
 
If you want anyone to confirm that, you'll have to show your detailed calculations. :smile:
 
GarrettKoep: Your current answer is incorrect. Try again.
 

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