physics
posted by Joseph .
A uniform horizontal bar of length L = 5 m and weight 243 N is pinned to a vertical wall and supported by a thin wire that makes an angle of theta = 39o with the horizontal. A mass M, with a weight of 300 N, can be moved anywhere along the bar. The wire can withstand a maximum tension of 600 N. What is the maximum possible distance from the wall at which mass M can be placed before the wire breaks?
I did (243x2) + 300x = 5*600 sin 39
x=4.67m but its incorrect and I don't know why ?

You're almost there.
The length of the bar is 5m.
In general, we assume the centroid to be in the middle, or 2.5 m from the wall.
You have put in 243*2.0 instead of 243*2.5
I'm sure you'd be OK after this correction.