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Question
A half metre rod is pivoted at the centre with two weights of 20gf and 12gf suspended at a perpendicular distance of 6 cm and 10 cm from the pivot respectively as shown below.
1) Which of the two forces acting on the rigid rod causes clockwise moment?
2) Is the rod in equilibrium?
3) The direction of 20 kgf force is reversed. What is the magnitude of the resultant moment of the forces on the rod?
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Solution
1) The force of 12 gf causes a clockwise moment.
2) Clockwise moment = 12 x 10 gf cm
= 120 gf cm
Anti clockwise moment = 20 x 6 gf cm
= 120 gf cm
∵ Clockwise moment = Anti clockwise moment
∴ The rod is in equilibrium.
3) If the direction of 20 gf force is reversed, it will also create a clockwise moment.
Resultant moment = (120 + 120) gf cm (clockwise)
= 240 gf cm
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