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Question
The diagram in Fig shows two forces F1 = 5 N and F2 = 3 N acting at points A and B respectively of a rod pivoted at a point O, such that OA = 2 m and OB = 4 m.
Calculate:
- the moment of force F1 about O.
- the moment of force F2 about O.
- total moment of the two forces about O.
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Solution
- Moment of force F1 about O = Force × AO
= 5N × 2m
= 10 Nm (anticlockwise) - Moment of force F2 at O = Force × BO
= 3N × 4m
= 12 Nm (clockwise) - Total moment of force at O
= clockwise moments − anticlockwise moments
= 12 Nm − 10 Nm
= 2 Nm (clockwise)
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Assertion & Reasoning
- Assertion: The sum of the clockwise moments is equal to the sum of the anticlockwise moments.
- Reason: The principle of conservation of momentum is valid if the external force on the system is zero.
