Principle of moments in equilibrium Steps: - The metre rule is uniform, so its weight W acts at the centre of mass (50 cm mark). - Assume the diagram shows the pivot at the 90 cm mark and the 4 N weight at the 100 cm mark. - Distance from pivot to centre of mass: 90 cm - 50 cm = 40 cm (or 0.4 m) to the left. - Distance from pivot to 4 N weight: 100 cm - 90 cm = 10 cm (or 0.1 m) to the right. - For balance, clockwise moment equals anticlockwise moment: W × 0.4 = 4 × 0.1. - Solve: W = (4 × 0.1) / 0.4 = 1 N. Why A is correct: - Moments balance when W × distance to CM equals 4 N × its distance, yielding W = 1 N per the torque equilibrium condition. Why the others are wrong: - B: Assumes equal weights, ignoring unequal lever arms. - C: Inverts the distance ratio (4 times larger than actual). - D: Multiplies unnecessarily by total length factor. …