S.O.S. Mathematics CyberBoard

I have a 5.5 inch diameter disk that rotates on a center axis, with an 18 inch bar that extends straight down from the center of the disk. A 50 pound weight hangs down off the (lower) end of the bar. A wire is secured at the left-most (9 o'clock) point on the disk, wraps on the outside of the disk, over the top (12 o'clock) and hangs down on the right side (3 o'clock) of the disk.

What force, pulling down on the wire, is necessary to initially move the weight, and what is the maximum force necessary to move the weight 180 degrees to the straight up position? Is there a formula I can use to calculate the force at any point?

Any help will be greatly apprciated. This is a real application and I need to purchase a linear actuator to move the weight.

Thanks,
Mike