Final answer:
To determine the magnitude of the moment of the force f about the corner a, calculate the torque using the formula μ = rF sinθ, where r is the lever arm and F is the force.
Step-by-step explanation:
To determine the magnitude of the moment of the force f about the corner a, we need to calculate the torque. Torque is equal to the product of the force and the lever arm (perpendicular distance from the axis of rotation). In this case, the torque is μ = rF sinθ, where r is the lever arm and F is the force.