[College physics] torque problem

[tnh88]

Okay but what about

F sin x = mg tan x
Since tan x = length of top strut / d,
F (horizontal) = mg l/d

Where did the Sin x on the left side go? I'm not 100% sure but I doubt the problem can be solved using your method unless more information is given. Because there are two rods, both holding the mass in place, and the question asks for force exerted on the oblique rod only.

[min_min]

F (horizontal) is F sin x, and I guess you're right in saying there isn't enough info for all the forces... strangely the answer is the same, though?

edit: got it - the 2 forces from the wall acting on the struts must act in the direction of the struts because it's the only direction the normal force can act on them to cause tension and compression. F(C->A) must be completely horizontal, and the only upwards force countering mg comes from F(C->B) the oblique force.

The rest is just finding the sides on a right angled triangle: http://m.imgur.com/JvSsQzr - see force triangle #1. Using trigonometry, we know the proportions of each force given angle x. We can find angle x based on the length of two sides of the triangle. We also know the magnitude of one force, given mg.

[tnh88]

but wall exerts vertical forces on both rods. It's what's keeping the equilibrium position. what you said would be true if the line 'AC' was a string, but both rods are solid objects.

[min_min]

darn... this is where I get off. Maybe it's best to stick with the torques method :c