Find the pressures Pд and PB at surfaces A and B in the tube, respectively. ○ Pgas, Patm O Patm, Patm PA, PB = O Pgas, Pgas +Patm OPgas, Pgas O Pgas +Patm, Patm Peas mercury A B 12

You are pumping up a bicycle tire with a hand pump, the piston of which has a 2.00-cm radius. (a) What force in newtons must you exert to create a pressure of 6.90105 Pa (b) What is unreasonable about this (a) result? (c) Which premises are unreasonable or inconsistent?

How many cubic meters of helium are required to lift a light balloon with a 400-kg payload to a height of 8 000 m? Take Hc = 0.179 kg/m3. Assume the balloon maintains a constant volume and the density of air decreases with the altitude z according to the expression pair = 0e-z/8 000, where z is in meters and 0 = 1.20 kg/m3 is the density of air at sea level.

Five bicyclists are riding at the following speeds: 5.4 m/s, 5.7 m/s, 5.8 m/s, 6.0 m/s, and 6.5 m/s. (a) What is their average speed? (b) What is their rms speed?

A manometer containing water with one end connected to a container of gas has a column height difference of 0.60 m (Fig. P15.72). If the atmospheric pressure on the right column is 1.01 105 Pa, find the absolute pressure of the gas in the container. The density of water is 1.0 103 kg/m3. FIGURE P15.72

(a) Using Bernoulli's equation, show that be measured fluid speed v for a pitot tube, like the one in figure 14.32(b), is given by v=( 2gh)1/h , where h is be height of be manometer fluid, p' is the density of the manometer fluid, p is the density of the moving fluid, and g is be acceleration due to gravity. (Note that v is indeed proportional to the square root of h, as stated in text) (b) Calculate v for moving air if a mercury manometer's h is 0.200 m. Figure 14.32 Measurement of fluid speed on Bernoulli’s principle. (a) A manometer is connected to two tubes close together and small enough not to disturb the flow. Tube 1 is open at the end facing the flow. A dead spot having zero speed is created there. Tube 2 has an opening on the side, so the fluid has a speed v across; thus, pressure there drops. The difference in pressure at the manometer is 12v22 , so h is proportional to . 12v22 (b) This type of velocity measuring device is a Prandtl tube, also known as a pitot tube.

(a) Calculate the absolute pressure at an ocean depth of 1 000 m. Assume the density of seawater is 1 030 kg/m3 and the air above exerts a pressure of 101.3 kPa. (b) At this depth, what is the buoyant force on a spherical submarine having a diameter of 5.00 m?

Verigy that the SI of hpg is N/m2.

A vertical cylinder of cross-sectional area A is fitted with a tight-fitting, frictionless piston of mass m (Fig. P18.40). The piston is not restricted in its motion in any way and is supported by the gas at pressure P below it. Atmospheric pressure is P0. We wish to find the height h in Figure P18.40. (a) What analysis model is appropriate to describe the piston? (b) Write an appropriate force equation for the piston from this analysis model in terms of P, P0, m, A, and g. (c) Suppose n moles of an ideal gas are in the cylinder at a temperature of T. Substitute for P in your answer to part (b) to find the height h of the piston above the bottom of the cylinder. Figure P18.40

Review. (a) Derive an expression for the buoyant force on a spherical balloon, submerged in water, as a function of the depth h below the surface, the volume Vi of the balloon at the surface, the pressure P0 at the surface, and the density w of the water. Assume the water temperature does not change with depth, (b) Does the bouyant force increase or decrease as the balloon is submerged? (c) At what depth is the buoyant force one-half the surface value?