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Why is the weight going upward? Statics

  • Thread starter asz304
  • Start date
  • #1
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Homework Statement



http://www.engr.mun.ca/~neil/1010/prob11/set2.pdf" [Broken]

In the first problem in the link above, why is the weight pointing upwards instead of downwards? I thought there will be a different force prolly called Fae pointing upwards with the weight pointing downwards.

Thanks
 
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Answers and Replies

  • #2
rock.freak667
Homework Helper
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In the first part I think they just used W to represent the force acting in the vertical chain connected to A.
 
  • #3
108
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But in the calculations, W = mg, where m = 200kg. I still dont get it...
 
  • #4
rock.freak667
Homework Helper
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Yeah I see it now. Not too sure why exactly they did that other than to get a positive answer. If you had W acting downwards, then you'd get the two forces to be negative meaning that the forces act in the opposite direction.
 
  • #5
nvn
Science Advisor
Homework Helper
2,128
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asz304: W points upward in the FBD of joint A because chain AE applies an upward force on point A, called Fae, where Fae = W. If you wish to write vector Fae, that is fine. And the magnitude of vector Fae is W; i.e., Fae = W.

By the way, always leave a space between a numeric value and its following unit symbol. E.g., 200 kg, not 200kg. See the international standard for writing units (ISO 31-0).
 
  • #6
1,033
1
W must mean Tension in the string. It can't be anything else.
 

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