Buoyancy and work in forced submersion Steps:

• Initially, cylinder floats with buoyant force equal to weight, partially submerged.
• Applying downward force F increases submersion, raising water level as more volume displaces water.
• Cylinder's center of mass lowers, reducing its gravitational potential energy.
• Buoyant force (thrust) acts upward while displacement is downward, so thrust does negative work on cylinder.

Why D is correct:

• Work by thrust is not zero; by work-energy theorem, $W = \vec{F} \cdot \vec{d}$, upward thrust and downward displacement yield negative (non-zero) work.

Why the others are wrong:

• A: Water displaced rises, gaining gravitational potential energy as level increases.
• B: Cylinder sinks deeper, lowering its center of mass and losing potential energy.
• C: Thrust performs work (negative) as cylinder moves against it.

Final answer: D