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Statics cable length problem

  • Thread starter sevag00
  • Start date
  • #1
80
1

Homework Statement



The window is held open by the cable AB. Determine the length of the cable and express the 30N acting at A along the cable as a Cartesian vector.
http://img802.imageshack.us/img802/9599/ru5y.jpg [Broken]

Homework Equations



vector(F) = FuAB

The Attempt at a Solution



Here's my solution
http://img833.imageshack.us/img833/6996/n7b0.png [Broken]
 
Last edited by a moderator:

Answers and Replies

  • #2
ehild
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Check the x and z coordinates of A.

ehild
 
  • #3
SteamKing
Staff Emeritus
Science Advisor
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Check the coordinates of B.
 
  • #4
80
1
Yeah the B coordinates should be B(0,150,250) but i don't know what's wrong with the A coordinates especially the z one.
 
  • #5
ehild
Homework Helper
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The plate is not horizontal, but inclined at 30°angle downward. 300 mm is the length of the edge.

ehild
 
  • #6
80
1
300mm is the length of the edge which is the x coordinate, just like 500 which is the y coordinate.
 
  • #7
gneill
Mentor
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300mm is the length of the edge which is the x coordinate, just like 500 which is the y coordinate.
Nope. Sketch the side view:

attachment.php?attachmentid=62900&stc=1&d=13817679824.gif


EDIT: Added point A to the diagram.
 

Attachments

Last edited:
  • #8
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But isn't the y of point A at the end of the window and not at 0?
 
  • #9
gneill
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But isn't the y of point A at the end of the window and not at 0?
Yes. The sketch is looking along the y-axis (the y-axis is coming straight out of the page), so all y-coordinates will be seen as flat against the x-z plane. Point A is at the end of the heavy line, not at the origin.
 
  • #10
80
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So in this case, what is the coordinate?
 
  • #11
gneill
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So the y coordinate will be 300, right?
How do you get that? I thought we were talking about the x and z coordinates for point A.
 
  • #12
gneill
Mentor
20,793
2,773
So in this case, what is the coordinate?
I modified my diagram to show the location of point A (I thought it was obvious, but it never hurts to clarify). What x and z coordinates would you assign to point A?
 
  • #13
80
1
So z=-300sin30 x=300cos30 and y=500.
 
  • #14
80
1
How do you get that? I thought we were talking about the x and z coordinates for point A.
No. That was stupid. I edited my post.
 
  • #15
gneill
Mentor
20,793
2,773
So z=-300sin30 x=300cos30 and y=500.
Yes, that looks better.
 
  • #16
80
1
Thanks for the help.
 

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