Principle of moments about the pivot Steps:

• Beam length 3.0 m, uniform, so center of gravity at 1.5 m from P; with O 1.0 m from Q, P to O is 2.0 m, placing center of gravity 0.5 m left of O.
• Beam weight 50 N acts 0.5 m left of O, giving anticlockwise moment: 50 × 0.5 = 25 Nm.
• Load W acts at Q, 1.0 m right of O, giving clockwise moment: W × 1.0 Nm.
• For rotational equilibrium, anticlockwise = clockwise: 25 = W × 1, so W = 25 N.

Why A is correct:

• Moments balance per the principle of moments, where torque = force × perpendicular distance to pivot.

Why the others are wrong:

• B: 50 N gives clockwise moment 50 Nm, exceeding 25 Nm anticlockwise.
• C: 75 N gives 75 Nm clockwise, far unbalanced.
• D: 100 N gives 100 Nm clockwise, maximally unbalanced.

Final answer: A