LEVEL B PROBLEMS

1) An airtight container having a lid with negligible mass and an area of 77 cm2 is partially evacuated. If a force of 480 N is required to pull the lid off and the surrounding atmospheric pressure is 1.0 x 105 Pa, what is the pressure in the container before it was opened? (47.7 kPa)

2) A hollow sphere of inner radius 8.0 cm and outer radius 9.0 cm floats half submerged in a liquid of density 800 kg/m3. (a) What is the mass of the sphere? (b) Calculate the density of the material of which the sphere is made? (1.2 kg, 1300 kg/m3)

3) A block of wood has a mass of 3.67 kg and a density of 600 kg/m3. It is to be loaded with lead so that it will float in water with 90% of its volume submerged. What mass of lead is needed (a) if the lead is attached to the top of the wood and (b) the lead is attached to the bottom of the wood? The density of lead is 1.13 x 104 kg/m3. (1.84 kg, 2.01 kg)

4) Water is pumped steadily out of a flooded basement at a speed of 5.0 m/s through a uniform hose of radius 1.0-cm. The hose passes out through a window 3.0 m above the waterline. What is the power of the pump? (66 W)

5) Water is moving with a speed of 5.0 m/s through a pipe with a cross-sectional area of 4.0 cm2. The water gradually descends 10-m as the pipe increases area to 8.0 cm2. (a) What is the speed at the lower level? (b) If the pressure in the upper level is 1.5 x 105 Pa, what is the pressure at the lower level? (2.5 m/s; 2.6 x 105 Pa).

6) An opening of area 0.25 cm2 in an otherwise closed beverage keg is 50 cm below the level of liquid (of density 1.0 g/cm3) in the keg. What is the speed of the liquid flowing through the opening if the gauge pressure in the air space above the liquid is (a) zero, (b) 0.40 atm? (3.1 ms/; 9.5 m/s)