Moment of a Force About a Pivot Point

Mediummomentscomponents

A 200 N force is applied at the end of a 0.75 m bar that pivots at O. The force acts at 60° to the bar. What is the magnitude of the moment about O?

A130 N·m
B150 N·m
C75 N·m
D173 N·m

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Answer: A. 130 N·m

Only the component perpendicular to the bar creates moment: F_perp = 200 · sin 60° = 173.2 N. Then M_O = F_perp · d = 173.2 · 0.75 = 129.9 ≈ 130 N·m. Using the full 200 N (150 N·m) ignores the angle; 173 N·m is the perpendicular force, not the moment.

M_{O}

= F_{⊥} \cdot d

= 200 sin 6 0^{\circ} \cdot 0.75

= 173.2 \cdot 0.75

= 130

N·m

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