How can we determine the rotational axis for a torques-related problem?

[oontvoo]

Homework Statement

(Please see attachment for the problem statement)
https://www.physicsforums.com/attachment.php?attachmentid=27212&stc=1&d=1280270933

The Attempt at a Solution

I do not see how we use the fact that the total torques balance when the rotational axis is through point A to find answer questions a) through d).
I mean, every variables are unknown...

So! ANyone got a hint?

 

[merryjman]

I feel that this is a conceptual rather than mathematical question, which is why no numbers or distances are given.

For example, if the torques are all balanced at O, that means the two torques which would tend to rotate it counterclockwise balance the single one that would rotate it clockwise (that's the one pointing down). Moving the axis to A means now you've got two torques which would rotate it clockwise, and one cc. And that one cc is a lot smaller, since lot weaker, since the distance between it and the axis has shortened.

Try to think about each scenario like that, reasoning carefully based on distances from axis and directions.