Verified Solution • 2025–26 Session moderate

Q9.9: NCERT Physics - Part 2 MECHANICAL PROPERTIES OF FLUIDS 9.9 Solution: A U-tube contains water and methylated spirit separated by…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently write the full hydrostatic balance including mercury terms (ρ_water g h_water + ρ_Hg g h_Hg = ρ_spirit g h_spirit + ρ_Hg g h'_Hg) and then try to solve for ρ_spirit, overlooking that the mercury columns are at the same height so the mercury pressures cancel; the correct relation is simply ρ_water h_water = ρ_spirit h_spirit.

A U-tube contains water and methylated spirit separated by mercury. The mercury columns in the two arms are in level with 10.0 cm of water in one arm and 12.5 cm of spirit in the other. What is the specific gravity of spirit?

Step-by-Step Verified Solution

**Answer:** 0.8 **Step-by-Step Explanation:** At the mercury level, pressures from both arms are equal:
ρwaterghwater=ρspiritghspirit\rho_{water} g h_{water} = \rho_{spirit} g h_{spirit}
With ρwater=1\rho_{water} = 1 g/cm_, hwater=10.0h_{water} = 10.0 cm, hspirit=12.5h_{spirit} = 12.5 cm:
ρspirit=10.012.5×1=0.8 g/cm3\rho_{spirit} = \frac{10.0}{12.5} \times 1 = 0.8 \text{ g/cm}^3
Specific gravity of spirit = 0.8.

All Questions in this Chapter

Q9.1 Q9.2 Q9.3 Q9.4 Q9.5 Q9.6 Q9.7 Q9.8 Q9.9 Q9.10 Q9.11 Q9.12 Q9.13 Q9.14 Q9.15 Q9.16 Q9.17 Q9.18 Q9.19 Q9.20

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