Page 213 - Schaum's Outline of Theory and Problems of Applied Physics

198 FLUIDS AT REST [CHAP. 16

Supplementary Problems

16.1. A sailboat has a lead keel to help keep it upright despite the pressure wind exerts on its sails. What difference, if any,
is there between the stability of a sailboat in freshwater and in seawater?

16.2. Dam A and dam B are identical in size and shape, and the water levels at both are the same height above their bases.
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Dam A holds back a lake that contains 1 km of water, and dam B holds back a lake that contains 2 km of water.
What is the ratio between the total force exerted on dam A and that exerted on dam B?
16.3. The containers shown in Fig. 16-2 are filled with water to the same height. Compare the pressures on the bottoms
of the containers.

Fig. 16-2

16.4. When a person drinks a soda through a straw, where does the force come from that causes the soda to move upward?
16.5. Why does a steel ship float when the density of steel is nearly eight times that of water? Why does it sink if it springs
a leak and water enters its hull?
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16.6. A 50-g gold bracelet is dropped into a full glass of water, and 2.6 cm of water overflows. What is the density of
gold? What is its specific gravity?

16.7. What is the mass of water in a swimming pool 7 m long, 3 m wide, and 2 m deep?
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16.8. The density of iron is 7.8 × 10 kg/m . (a) What is the specific gravity of iron? (b) How many cubic meters does
1 metric ton (1000 kg) of iron occupy?
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16.9. The weight density of ice is 58 lb/ft . What is its specific gravity?
16.10. A nail 2 mm in diameter is embedded in a tire in which the gauge pressure is 1.8 bar. How much force tends to push
the nail out?
16.11. A 130-lb woman balances on the heel of one shoe, which is 1 in. in radius. How much pressure does she exert on
the floor?
16.12. A phonograph needle whose point is 0.1 mm (10 −4 m) in radius exerts a downward force of 0.02 N. What is the
pressure on the record groove? How many atmospheres is this?
16.13. A hypodermic syringe whose cylinder is 10 mm in diameter is used to inject a liquid into a patient’s vein in which
the blood pressure is 2 kPa. (a) What is the minimum force needed on the plunger of the syringe? (b) Why is the
diameter of the needle irrelevant?

16.14. The pressure of the blood in a patient’s vein is 12 torr. Find the minimum height above the vein that a container of
plasma must be held for the plasma to enter the vein. (The actual height is always much greater in order to have a
reasonable flow of plasma.)

16.15. What is the pressure at a depth of 100 m in the ocean? How many atmospheres is this? The density of seawater is
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1.03 × 10 kg/m .