Work equals force times displacement in the force's direction

Steps:

• Work done by a force is force magnitude times displacement magnitude when aligned.
• Worker applies force P over distance d along the rope.
• Block rises h, but worker's effort is on the rope, not the block directly.
• Thus, worker's work is P multiplied by d.

Why B is correct:

• Pd matches the work-energy definition: work by applied force equals force times parallel displacement.

Why the others are wrong:

• A: Ph uses block's height h, ignoring rope pull distance d.
• C: (P + W)h adds weight and uses h, confusing total system energy with worker's input.
• D: (P - W)d subtracts weight for net force, but worker expends full P over d.

Final answer: B