# Torque and Equilibrium

1. Oct 25, 2014

### iPromise

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

You are designing the crosspiece for the A-frame structure in the figure below. Beams AB and AC are 5.00 m long and have a mass of 375.0 kg each. How much tension must the crosspiece EF withstand? Assume that the mass of the crosspiece and the friction at points B and C are negligible.

http://oi57.tinypic.com/2zfq4y8.jpg

2. Relevant equations

T = F*R*sinΘ
∑T = 0

3. The attempt at a solution

I took the first half of the frame into consideration. I chose point A to be my pivot point. There are three forces acting on the first-half of the frame:

http://oi59.tinypic.com/fu7sw0.jpg

My initial equation:

(N)(4.75)(cosΘ) - (Mg)(2.375)cosΘ = (T)(1.4)

Θ = sin-1 ( 2.2 / 4.75 )
= 27.59

N = the force of gravity of the first half of the structure
= Mg = 335 * 9.81

I solve for T:

T = 4941.08

2. Oct 25, 2014

### Staff: Mentor

Where are you getting 4.75 and 1.4?

3. Oct 25, 2014

### iPromise

4.75 is the length of the ladder. 1.4 was the radius from the pivot point. That was my mistake, 1.4 is NOT the radius, 0.8 is.

4. Oct 25, 2014

### Staff: Mentor

Isn't it given as 5 m?

5. Oct 25, 2014

### iPromise

Sorry I was thinking of the last practise version I did. Each version has different values.