Engineering Statics

B-16


A farmer uses a rope and pulley to lift a bale of hay of mass 28 kg. Determine the moment about point A of the resultant force exerted on the pulley by the rope if the center of the pulley C lies .4 m below point B and 7.2 m above the ground.

The simplified free-body diagram is easier to interpret.  The 
weights are calculated by multiplying the mass by g (9.8m/s/s).
The force can be written in vector form by remembering that the 
components of the force form a similar triangle with the components 
of the distances defining the rope.
Substitution and simplification yield the force in vector form.
The radius can also be written in vector form.
The moment is evaluated as a determinant.
Solving the determinant gives the moment.