If the atmospheric pressure on the surface of an oil tank (Sp. Gr. 0.8) is 0.1 kg/cm², then the pressure at a depth of 2.5 m is
- A1 metre of water
- B2 metres of water
- C3 metres of waterCorrect
- D3.5 metres of water
Solution
Concept
Pressure head of an oil column
Formula
p/γw = p0/γw + s × h
Step-by-step solution
1. Surface pressure 0.1 kg/cm² = 1 m of water. 2. Pressure due to 2.5 m of oil of sp. gr. 0.8 = 0.8 × 2.5 = 2 m of water. 3. Total = 1 + 2 = 3 m of water.
Explanation
Pressure heads can be added when they are expressed in the same liquid. The oil column of specific gravity 0.8 is equal to 0.8 times its height in water. The atmospheric pressure of 0.1 kg/cm² (the printed unit "kg/cm" means kg/cm²) is 1 m of water.
Shortcut
Convert everything to metres of water: 1 + 0.8 × 2.5 = 3.
Common mistake
Forgetting to multiply by the specific gravity.
Correct answer: C) 3 metres of water