# Statics cable length problem

1. Oct 14, 2013

### sevag00

1. The problem statement, all variables and given/known data

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]

2. Relevant equations

vector(F) = FuAB

3. The attempt at a solution

Here's my solution
http://img833.imageshack.us/img833/6996/n7b0.png [Broken]

Last edited by a moderator: May 6, 2017
2. Oct 14, 2013

### ehild

Check the x and z coordinates of A.

ehild

3. Oct 14, 2013

### SteamKing

Staff Emeritus
Check the coordinates of B.

4. Oct 14, 2013

### sevag00

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. Oct 14, 2013

### ehild

The plate is not horizontal, but inclined at 30°angle downward. 300 mm is the length of the edge.

ehild

6. Oct 14, 2013

### sevag00

300mm is the length of the edge which is the x coordinate, just like 500 which is the y coordinate.

7. Oct 14, 2013

### Staff: Mentor

Nope. Sketch the side view:

EDIT: Added point A to the diagram.

#### Attached Files:

• ###### Fig1.gif
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Last edited: Oct 14, 2013
8. Oct 14, 2013

### sevag00

But isn't the y of point A at the end of the window and not at 0?

9. Oct 14, 2013

### Staff: Mentor

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. Oct 14, 2013

### sevag00

So in this case, what is the coordinate?

11. Oct 14, 2013

### Staff: Mentor

How do you get that? I thought we were talking about the x and z coordinates for point A.

12. Oct 14, 2013

### Staff: Mentor

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. Oct 14, 2013

### sevag00

So z=-300sin30 x=300cos30 and y=500.

14. Oct 14, 2013

### sevag00

No. That was stupid. I edited my post.

15. Oct 14, 2013

### Staff: Mentor

Yes, that looks better.

16. Oct 14, 2013

### sevag00

Thanks for the help.