Question Detail
Question
A uniform metre rule AB is supported at its centre of gravity by a knife edge. A force of 4 N is applied at a point which is 20 cm from end A of the rule. Calculate the force which must be applied to end B to restore the equilibrium of the rod.
Correct Answer
Option A is the correct answer.
Detailed Explanation
Pivot at centre (50 cm). Force at 20 cm from A is at 20 cm mark, distance from pivot = 30 cm. Moment = 4 × 30 = 120 N·cm. Force at B (100 cm mark) distance from pivot = 50 cm. For equilibrium: F × 50 = 120 → F = 2.4 N. Option C is 2.4 N.
Hint
Take moments about the centre.