91Ó°ÊÓ

A barge filled high with sand approaches a low bridge over the river and cannot quite pass under it. Should sand be added to, or removed from, the barge? [Hint: Consider Archimedes’ principle.]

An airplane has a mass of \({\bf{1}}{\bf{.7 \times 1}}{{\bf{0}}^{\bf{6}}}\;{\bf{kg}}\) and the air flows past the lower surface of the wings at 95 m/s. If the wings have a surface area of \({\bf{1200}}\;{{\bf{m}}^{\bf{2}}}\), how fast must the air flow over the upper surface of the wing if the plane is to stay in the air?

A drinking fountain shoots water about 12 cm up in the air from a nozzle of diameter 0.60 cm (Fig. 10–57). The pump at the base of the unit (1.1 m below the nozzle) pushes water into a 1.2-cm-diameter supply pipe that goes up to the nozzle. What gauge pressure does the pump have to provide? Ignore the viscosity; your answer will therefore be an underestimate.

A hurricane-force wind of \({\bf{180}}\;{\bf{km/h}}\) blows across the face of a storefront window. Estimate the force on \({\bf{2}}{\bf{.0}}\;{\bf{m \times 3}}{\bf{.0}}\;{\bf{m}}\) the window due to the difference in air pressure inside and outside the window. Assume the store is airtight so the inside pressure remains at 1.0 atm. (This is why you should not tightly seal a building in preparation for a hurricane.)

Blood is placed in a bottle 1.40 m above a 3.8-cm-long needle, of inside diameter 0.40 mm, from which it flows at a rate of \({\bf{4}}{\bf{.1}}\;{\bf{c}}{{\bf{m}}^{\bf{3}}}{\bf{/min}}\). What is the viscosity of this blood?

A copper (Cu) weight is placed on top of a 0.40-kg block of wood (\({\bf{density = 0}}{\bf{.60 \times 1}}{{\bf{0}}^{\bf{3}}}\;{\bf{kg/}}{{\bf{m}}^{\bf{3}}}\) ) floating in water, as shown in Fig. 10–58. What is the mass of the copper if the top of the wood block is exactly at the water’s surface?

Figure: 10-58

You need to siphon water from a clogged sink. The sink has an area of and is filled to a height of 4.0 cm. Your siphon tube rises 45 cm above the bottom of the sink and then descends 85 cm to a pail as shown in Fig. 10–59. The siphon tube has a diameter of 2.3 cm. (a) Assuming that the water level in the sink has almost zero velocity, use Bernoulli’s equation to estimate the water velocity when it enters the pail. (b) Estimate how long it will take to empty the sink. Ignore viscosity.

As water flows from a low elevation to a higher elevation through a pipe that changes in diameter,

(a) The water pressure will increase.

(b) The water pressure will decrease.

(c) The water pressure will stay the same.

(d) Need more information to determine how the water pressure changes.

(I) Estimate the pressure exerted on a floor by (a) a one-pointed heel of area = 0.45 cm², and (b) one wide heel of area 16 cm², Fig. 10–48. The person wearing the shoes has a mass of 56 kg.

Explain why helium weather balloons, which are used to measure atmospheric conditions at high altitudes, are normally released while filled to only 10–20% of their maximum volume.