Why Is the Moment Negative in Case 2 Despite Using the Right Hand Rule?

[engineer_dave]

Homework Statement

How do u find whether the moment is negative or positive in the three examples shown?? Even if you use the right hand rule, for case 2 i have seen that the moment is negative and not positive. I am taking counter clockwise as positive moments. Please help out. Thanks!

Homework Equations

The Attempt at a Solution

 

[PhanthomJay]

Homework Statement

How do u find whether the moment is negative or positive in the three examples shown?? Even if you use the right hand rule, for case 2 i have seen that the moment is negative and not positive. I am taking counter clockwise as positive moments. Please help out. Thanks!

If you take ccw as positive, then the moment vector points out of the page toward you, using the right hand rule, in the positive Z direction. It follows that cw moments are then negative, pointing in the negative Z direction into the page away from you. So the first 2 moments, being cw are negative, and the last, being ccw, is positive, per your chosen convention.