Torque of a Couple

Steps:

• Identify a couple as two equal, opposite forces separated by a distance.
• Recall the torque formula for a couple: magnitude of one force times perpendicular distance between their lines of action.
• Note that the net force is zero, but torque is nonzero and independent of pivot point.
• Match formula to options: B directly states force × perpendicular distance.

Why B is correct:

• The standard formula for couple torque is τ = F × d, where F is the magnitude of one force and d is the perpendicular distance between forces.

Why the others are wrong:

• A: Uses half the distance, underestimating torque.
• C: Sum of forces is zero for a couple, yielding zero torque incorrectly.
• D: Multiplies by 2, doubling the torque beyond the formula.

Final answer: B