1. Jul 5, 2009

### NikkiNik

1. The problem statement, all variables and given/known data
A mass M=171 kg is suspended from the end of a uniform boom as shown. The boom (mass=83.0 kg, length=2.40 m) is at an angle θ=69.0 deg from the vertical, and is supported at its mid-point by a horizontal cable and by a pivot at its base. Calculate the tension in the horizontal cable.

http://i32.photobucket.com/albums/d2/NikkiNik88/staticsboom.gif

2. Relevant equations

T=rsin(theta)

3. The attempt at a solution

Theta = 69 deg, alpha=21 deg

mg(L/2)cos(theta) + Mg(L)cos(theta) + T(L/2)sin(alpha) = 0

2. Jul 5, 2009

### ideasrule

Why are you using cosine for mg(L/2) and sine for the others, instead of the other way round? Think more carefully about which functions you should use.

3. Jul 5, 2009

### NikkiNik

Would I be using sine for the masses because they are vertical and cosine for the tension because it's horizontal? If that's the case, is the rest of my work correct if I switch sine and cosine?

4. Jul 5, 2009

### ideasrule

Yes! So:

mg(L/2)sin(theta) + Mg(L)sin(theta) + T(L/2)cos(theta) = 0

The answer you get will be negative, but that's only because the tension acts to counteract the torque applied by gravity.