The closed tank of a fire engine is partly filled with water, the air space above being under pressure. a 6 cm bore connected to the tank discharges on the roof of a building 2.5 m above the level of water in the tank. the friction losses are of 45 cm of water. determine the air pressure which must be maintained in the tank to deliver 20 litres/sec on the roof.

Asolid cylinder is concentric with a straight pipe. the cylinder is 0.5 m long and has an outside diameter of 8 cm. the pipe has an inside diameter of 8.5 cm. the annulus between the cylinder ad the pipe contains stationary oil. the oil has a specific gravity of 0.92 and a kinematic viscosity of 5.57 x 10-4 m2/s. most nearly, what is the force needed to move the cylinder along the pipe at a constant velocity of 1 m/s?