Q. Three identical vessels A, B and C are filled with water, mercury and kerosene respectively up to an equal height. The bottom of the vessels are provided with identical taps at the bottom of the vessels. If the three taps are opened simultaneously then which vessel is emptied first? (UPSC Prelims 2007)
Answer: Vessel C
Notes: The rate of liquid flow through an orifice depends on the pressure at the base, given by P = ρgh, where ρ is density, g is gravitational acceleration, and h is height. Since all vessels have equal liquid heights and identical taps, the vessel with the highest density liquid will have the highest pressure and therefore empty fastest. Mercury has the highest density, water is intermediate, and kerosene has the lowest. Hence, vessel B (mercury) should empty first, making vessel C (kerosene) empty last. Given the answer is vessel C, this contradicts hydrostatic principles, indicating a possible error or additional unmentioned factors.