Tank mixing dynamics

(1)               A tank contains 2 m3 of pure water initially. A stream of brine containing 25 kg/m3 of salt is fed into the tank at a rate of 0.02 m3/s. Liquid flows from the tank at a rate of 0.01 m3/s. If the tank is well mixed, what is the salt concentration (kg/m3) in the tank when the tank contains 4 m3 of brine.

(2)               Into a 1000-gal tank, initially filled with 100 gal of fresh water (density = 62.4 lb/ft3), saltwater containing 1.92 lb/gal of salt flows at a fixed rate of 4.0 GPM. The density of the incoming solution is 71.807 lb/ft3. The solution, kept uniform by stirring, flows out at a fixed rate of 19.2 lb/min. How many pounds of salt will there be in the tank at the end of 90 minutes? 1 ft3 = 7.48 gal.

Fluid Statics

(3)               Absolute pressure at sea level = 101,325 Pa. Gravity = 9.81 m/s2, Molecular weight of air = 29. Gas constant = 8.314 J/mol/K. Calculate the absolute pressure at a location 100 m above the sea level assuming isothermal air at 293 K.