Why is the weight going upward? Statics

[asz304]

Homework Statement

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

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

 

[rock.freak667]

In the first part I think they just used W to represent the force acting in the vertical chain connected to A.

 

[asz304]

But in the calculations, W = mg, where m = 200kg. I still don't get it...

 

[rock.freak667]

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.

 

[nvn]

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[/color] (ISO 31-0[/color]).

 

[dacruick]

W must mean Tension in the string. It can't be anything else.