Maximum torque from parallel forces occurs with maximum separation

Steps:

• Recognize two equal parallel forces in opposite directions create a couple with torque τ = F × d, where d is perpendicular distance between force lines.
• Note rod length Sd sets maximum possible d as Sd, achieved when forces act at opposite ends.
• Compare diagrams: evaluate d for each force pair relative to rod length.
• Select diagram with largest d for maximum τ.

Why D is correct:

• D places forces at rod ends in opposite directions, yielding d = Sd and τ = F × Sd per couple torque formula.

Why the others are wrong:

• A: Forces near one end, d much less than Sd, smaller τ.
• B: Forces mid-rod or same side, minimal d, near-zero τ.
• C: Forces at intermediate points, d < Sd, reduced τ.

Final answer: D