# Equilibrum question help here?

1. Jun 28, 2012

### Questions999

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

We have a bar with the weight of 500 N which stands in A and B.In this bar an object which weights 1500 N has been hung.The length of the bar AB is 2 meters and AD is 0.8 meters.Find FA and FB just like in the picture.

http://s1171.photobucket.com/albums/r549/Elaia06/?action=view&current=sdsd.jpg

3. The attempt at a solution

The resultant momentum is zero so

FA*0+1900*0.8+500*1+2*FB=0
But FB in my book is 850 N.This answer does not fit my answer.

2. Jun 28, 2012

### Staff: Mentor

(1) Why 1900?
(2) Distinguish clockwise and counterclockwise moments: they have different signs.

3. Jun 29, 2012

### Questions999

it is 1900 sorry , I have written it the wrong way in the data.
FA*0-1900*0.8-500*1+2*FB=0
Still FB is not 860..

4. Jun 29, 2012

### azizlwl

Your drawing is not clear enough.
Maybe you make the drawing, take a snapshot and insert image.

5. Jun 29, 2012

### Staff: Mentor

Are you sure? When I solve for FB using your original data (weight of object = 1500N) I get FB = 850 N. Which matches the answer in your book (at least according to your first post).

6. Jun 29, 2012

### Questions999

i have written it wrong ,i was sleepy last night :P
It should be 860 N, the Fb.
Yes I get 850 N too.The drawing is just like in my book.

7. Jun 29, 2012

### Questions999

Not related to this exercise :Ah and by the way, If we have a bar with two forces acting in the begining and the end of it, what is the relationship of the weight of the bar with the forces? I mean, is the distance from a force to the point of weight equal to the distance of the other force with the weight or not?

8. Jun 29, 2012

### Staff: Mentor

If the bar is uniform, the weight acts at its center. The support forces at each end will (of course) be equidistant from the center.

9. Jun 29, 2012

### Questions999

what is a uniform bar? Sorry but english is not my native language :P

10. Jun 29, 2012

### Staff: Mentor

A bar whose weight is evenly distributed along its length.

11. Jun 29, 2012

### Questions999

Yes this is an uniform bar, thanks :)