Determine the moment of each of the three forces about point A.
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Let us first draw the components of each force that is perpendicular to our reference point A. Components which pass through our reference will not be drawn as they do not create a moment about the said point.
The dashed lines show each component of the force which creates a moment about point A.
Let us look at force F_1. In this force, only the y-component creates a moment about point A. The x-component of force F_1 passes through line of action of point A. Thus, the moment created by force F_1 is:
We will now look at force F_2. As with force F_1, only the y-component of force F_2 creates a moment about point A.
Finally, let us look at force F_3. Notice how the x and y-components of force F_3 creates moments about point A. The x-component has a perpendicular distance of 4 m, and the y-component has a perpendicular distance of 5 m. It’s also important to note that the x-component will create a negative moment, or rather an opposite moment than the other forces because it will spin the bent arm counter clockwise about point A.
F_2:\circlearrowright M_A=1299 N\cdotm \circlearrowright
F_3:\circlearrowright M_A=800 N\cdotm \circlearrowright