Final answer:
To determine the moment about point A of each of the three forces acting on the beam, multiply each force by the distance from point A to the line of action of the force, determine the direction of rotation, apply the appropriate sign, and add up the individual moments.
Step-by-step explanation:
To determine the moment about point A of each of the three forces acting on the beam, we need to consider the torque produced by each force. Torque is defined as the product of the force and the perpendicular distance from the point of rotation (point A) to the line of action of the force. If the force produces a counterclockwise rotation, the torque is positive; if it produces a clockwise rotation, the torque is negative.
To find the moment about point A, multiply each force by the distance from point A to the line of action of the force. Then, determine the direction of rotation (clockwise or counterclockwise) and apply the sign convention. Finally, add up the individual moments to get the total moment about point A.