Hydrostatic pressure increases linearly with depth

Steps:

• Total liquid volume is 80 cm³, corresponding to total height H (assuming uniform cross-section).
• The 60 cm³ mark is at height (60/80)H = 0.75H from the base.
• Depth from surface to 60 cm³ mark is H - 0.75H = 0.25H; pressure there is ρg × 0.25H = 120 Pa.
• Depth at base is H, so pressure is ρg × H = 120 Pa / 0.25 = 480 Pa.

Why D is correct:

• Hydrostatic pressure formula P = ρgh shows pressure proportional to depth; base depth is 4× that at 60 cm³ mark, so 4×120 Pa = 480 Pa.

Why the others are wrong:

• A: Equals pressure at 60 cm³ mark, ignores additional depth to base.
• B: Assumes incorrect depth ratio (e.g., 80/60), underestimates by factor of 3.
• C: Assumes depth ratio of 3 (e.g., 60/20), overestimates partial depth.

Final answer: D