Homework Help: Static Equilibrium

1. Oct 28, 2009

G-reg

1. The problem statement, all variables and given/known data
In the figure below, a uniform beam of weight 520 N and length 3.4 m is suspended horizontally. On the left it is hinged to a wall; on the right is it supported by a cable bolted to the wall at distance D above the beam. The least tension that will snap the cable is 1200 N.

What value of D corresponds to that tension?

2. Relevant equations

$$\Sigma$$F in the x direction = 1200

3. The attempt at a solution
That equation is a guess within itself..I really have no clue how I should go about solving this problem..

2. Oct 29, 2009

ideasrule

The beam is in static equilibrium; it's not moving and not accelerating. Because of that, the sum of the forces be in the x and y directions must be 0.

That said, I don't think using forces is the best way to approach this problem. Try using torque: because the beam is not rotating, torque must be zero about any reference frame.

3. Oct 29, 2009

G-reg

Oh ok so I would set it up like this,

$$\Sigma\tau$$ = 3.0meters(mg) + ???

The question marks meaning that I don't know what to put after that first 3meters multiplied by mass times gravity.