M2 Point C Moment Calculation: Why is it Not the Same as Book?

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Homework Help Overview

The discussion revolves around calculating moments in a mechanics problem, specifically focusing on the moment at point C compared to the moment at point D. Participants are examining the differences in their calculations and questioning the accuracy of values derived from a diagram.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to calculate moments about points C and D, questioning the direction of forces and displacement vectors involved. There is a focus on discrepancies between personal calculations and those presented in a textbook.

Discussion Status

The discussion is ongoing, with participants providing insights and clarifications regarding the forces and vectors involved. Some participants are exploring different interpretations of the problem setup, while others are questioning the accuracy of the diagram and its implications for their calculations.

Contextual Notes

There are indications of confusion regarding the diagram's clarity and the values associated with the forces at points C and D. Participants are also reflecting on the potential inaccuracies in the triangle depicted in the diagram.

werson tan
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Homework Statement


for M2 , if i take the moment at pont C , then my ans would be (0.3i) x ((125X(3/5) j +125(4/5) k )= 30j +22.5k
Which is not same with the book which use moment about D . why ? Is the value at the triangle at te upper part incorrect (circle part) ?

Homework Equations

The Attempt at a Solution

 

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Picture is too small to read.
 
paisiello2 said:
Picture is too small to read.
 

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Still too small. Just blow up the diagram.
 
If you are taking moments about C then presumably you are considering the force at D. Isn't that in the direction -3/5j+4/5k? And should't the displacement vector be -3i?
 
haruspex said:
If you are taking moments about C then presumably you are considering the force at D. Isn't that in the direction -3/5j+4/5k? And should't the displacement vector be -3i?
Ya, I would ended up getting 22.5k +30j . But if I take moment about D , I would get 22.5j+30k... Is it correct?
 
werson tan said:
Ya, I would ended up getting 22.5k +30j . But if I take moment about D , I would get 22.5j+30k... Is it correct?
No, sorry, I had it wrong. The force at D is in the direction -4/5j+3/5k.
 

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