F1 is trying to cause a rotation around O.

the moment of the force is the product of the size of the force times the perpendicular distance from O to the line of action of the force

You can use trig to get d.

Bob

Sometimes it is easier to split F1 into a horizontal component (F1cos30) and a vertical component (F1sin30) and then get the moment of each.

As the vertical component acts through O it will have zero moment.

If you do it this way you'll get the same answer so it would be worth trying both just for the practice.

]]>I don't understand :"Find the torque (or "moment") of force F1 about the axis through point O"

Please solve with steps

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