Question

Three equal forces P, Q and R act in a plane but in different directions. The point O also lies in the same plane. Which force has the least moment about O? Which force has the largest moment about O? Give reasons to your answer.

Answer 1

The moment of a force depends on two factors:

Moment of Force = Magnitude of Force × Perpendicular distance (d)

Since all three forces are equal in magnitude (P = Q = R), their moments dependdirectly on the perpendicular distance from the pivot point O to their respective lines of action.

1. Force P has the largest moment about the point O.

Reason: The line of action of force P is located at the maximum perpendicular distance from the pivot point O, which results in the maximum turning effect.

2. Force Q has the least moment about the point O.

Reason: The line of action of force Q passes closest to the pivot point O, meaning its perpendicular distance is the shortest, which results in the minimum turning effect.