Question

A ballerina weighs 103 lbs and is up on her toes with only 10.0 cm^2 of her slippers in contact with the floor. What pressure is she exerting on the floor? Mineral oil can be used in place of mercury in manometers when small pressure changes are to be measured. What is the pressure of an oxygen sample in mm of mineral oil if its pressure is 28.5 mm Hg? (d of mineral oil = 0.88 g/mL; d of Hg = 13.5 g/mL) The answer: 437 mm mineral oil Your working out: A flask containing neon gas is connected to an open-ended mercury manometer. The open end is exposed to the atmosphere, where the prevailing pressure is 745 torr. The mercury level in the open arm is 50, mm below that in the arm connected to the flask of neon. What is the neon pressure, in torr?

Answer 1

Pressure = Force/Area 103 lbs = 46.72 kg (SI unit) Force = mg = 46.72 kg times 9.01 m/s^2 = 458.3232 N Area = 10.0 cm^2 = 10 times 10^-4 m^3 Pressure = 458.3232 N/10 times 10^-4 m^3 = 4.5832 times 10^5 Pa almost equal to 4.59 times 10^5 Pa Ans = 2 Pressure can also be written as P = Pgh P = density of liquid g = 9.81 m/s^2 h = height of liquid Now, Pressure is need in term of height of mineral oil P_oil = P_mercury both pressure are same as essentially we sant mm Hg pressure in term of mineral oil height \r\n P_mercury = 13.5 g/mL times 9.81 times 28.5 mm P_oil = 0.88 g/mL times 9.81 times h 0.28 times 9.81 times h = 13.5 times 9.81 times 28.5 h = 13.5 times 9.81 times 28.5 mm/0.88 times 9.81 = 437.21 mm \r\n