Buoyancy decreases as immersed volume reduces

Steps:

• At d=0, cylinder fully immersed; tension R = mg - ρVg (max buoyancy).
• As d increases to L, immersed height decreases linearly, so buoyancy drops linearly, R increases linearly to mg.
• For d > L, cylinder fully above water; buoyancy=0, R=mg constant.
• Graph shows linear rise then plateau.

Why C is correct:

• Matches Archimedes' principle: R rises linearly with decreasing displaced volume until fully emerged, then constant.

Why the others are wrong:

• A: Constant R ignores buoyancy change.
• B: Decreasing R contradicts tension increase from reduced buoyancy.
• D: Sudden jump violates gradual immersion reduction.

Final answer: C