Equilibrium and principle of moments

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Discussion Overview

The discussion revolves around the concept of equilibrium and the principle of moments in a physics homework problem. Participants are analyzing a scenario involving forces and torques acting around a pivot point, with a focus on understanding the role of a specific force, F, in the calculations.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant states that the moment on the left side of the pivot must equal the moment on the right side, leading to the equation (Fx.2)+(5x.14) = (7xd).
  • Another participant suggests that the question is poorly worded, noting that in part (b), F replaces the 5N force, implying that F does not exist in part (a).
  • A different participant points out that if F exists in part (a), the problem cannot be solved as there are two unknowns with only one equation available.
  • Another participant clarifies that F is relevant only to part (b) and that the diagram serves a dual purpose, indicating that F is not factored into the working for part (a).

Areas of Agreement / Disagreement

Participants express differing interpretations of the problem, particularly regarding the existence and role of force F in the calculations. There is no consensus on whether F should be included in the analysis for part (a), and the discussion remains unresolved.

Contextual Notes

Participants highlight potential ambiguities in the wording of the problem and the implications for solving it. The dependence on the interpretation of the problem statement and the roles of the forces involved is noted.

Apple&Orange
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Homework Statement



upload_2016-5-14_20-34-7.png


Homework Equations



Torque = F x D
Manticlockwise = Mclockwise

The Attempt at a Solution



From what I understand, the moment on left hand side of the pivot point needs to be equal to the moment on right hand side, therefore...

(Fx.2)+(5x.14) = (7xd)

My initial thinking was to substitute 2N into F, so that both forces on either side of pivot point are equal to 7N. However, this was not correct because the resultant forces were not in equilibrium after checking.

The answer in the book was this:
[/B]
upload_2016-5-14_21-16-11.png


Could someone explain to me why F wasn't factored into the working? The way I'm interpreting this is that there is no force acting at point F. Would this be a correct assumption?
 
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Looks like a badly worded question to me.

If you read Question (b) it says F replaces the 5N force. So F doesn't exist for question (a) ?
 
Apple&Orange said:
(Fx.2)+(5x.14) = (7xd)

If F does exist for (a) then that's correct but you can't solve it. You have one equation and two unknowns so best you can do is write an equation for d in terms of F.
 
Apple&Orange said:
Could someone explain to me why F wasn't factored into the working?
Part (b) explains that F acting at a distance 200mm is used in (b) as the substitute for the 5N force at a distance 140mm.

So the diagram is doing double-duty, and F is relevant only to part (b).
 

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