# Torque Truss Question

1. Jan 31, 2006

### Jordan_

Okay, I have uploaded the question to imageshack because it would be to difficult to understand the question without the diagram. Basically, I've done a lot of work on it and know I'm on the right track. If someone could point out where I have made a mechanical error it would be greatly appreciated. The question I am on is number 3.22, the one in the top right corner of the page.

Go here for picture of question.

So first off I made a free body diagram. Two Fn's going up, two 150's going down and a 500 going down. I solved for Fn and got 400N.

Then I solved the triangle to find that the angle between the cord and the board is 54 degrees. Finally I did torque calculations as follows:

T1 = 400(Fn) * 3 * sin 36
T1 = -705N

T2 = T * 2.5 * sin 54
T2 = 2.02T

2.02T = 705
T = 349N?

The answer should be 280 Newtons. Where have I gone wrong?

2. Jan 31, 2006

### Staff: Mentor

What about the torque due to the weight of the rafters?

3. Jan 31, 2006

### Jordan_

Damnit. I knew I forgot something.

Haha thanks bud!