Torque Calculation via Moment Arm

Steps:

• Identify pivot at O and force F applied at W on the rod.
• Determine the perpendicular distance (moment arm) from O to the line of action of F.
• Calculate torque magnitude as τ = F × d, where d is the moment arm.
• Determine rotation direction using right-hand rule: curl fingers from rod toward F, thumb shows axis direction.

Why B is correct:

• B matches τ = r F sinθ, where θ is the angle between position vector r (from O to W) and F, per torque definition.

Why the others are wrong:

• A uses full rod length instead of perpendicular distance, overestimating torque.
• C assumes force is parallel to rod, yielding zero torque incorrectly.
• D reverses rotation direction, ignoring right-hand rule convention.

Final answer: B