Chapter 3 Tutorial Problems

Fluid Mechanics
Tutorial Problems Set 3
3–7 The piston of a vertical piston-cylinder device containing a gas has a mass of 40 kg and a cross-sectional area
of 0.012 m2 (Fig P3–7). The local atmospheric pressure is 95 kPa, and the gravitational acceleration is 9.81 m/s2.
(a) Determine the pressure inside the cylinder. (b) If some heat is transferred to the gas and its volume is
doubled, do you expect the pressure inside the cylinder to change?
3–8 A vacuum gage connected to a chamber reads 36 kPa at a location where the atmospheric pressure is 92 kPa.
Determine the absolute pressure in the chamber.
3–12 The water in a tank is pressurized by air, and the pressure is measured by a multifluid manometer as shown in
Fig. P3–12. Determine the gage pressure of air in the tank if h1 = 0.4 m, h2 = 0.6 m, and h3 = 0.8 m. Take the densities
of water, oil, and mercury to be 1000 kg/m3, 850 kg/m3, and 13,600 kg/m3, respectively.
3–13 Determine the atmospheric pressure at a location where the barometric reading is 735 mmHg. Take the density
of mercury to be 13,600 kg/m3.
3–14 The gage pressure in a liquid at a depth of 3 m is read to be 28 kPa. Determine the gage pressure in the same
liquid at a depth of 12 m.
3–24 Water from a reservoir is raised in a vertical tube of internal diameter D = 30 cm under the influence of the
pulling force F of a piston. Determine the force needed to raise the water to a height of h = 1.5 m above the free
surface. What would your response be for h = 3 m? Also, taking the atmospheric pressure to be 96 kPa.
3–26 The basic barometer can be used to measure the height of a building. If the barometric readings at the top and
at the bottom of a building are 730 and 755 mmHg, respectively, determine the height of the building. Assume an
average air density of 1.18 kg/m3.
1
3–28 Determine the pressure exerted on a diver at 20 m below the free surface of the sea. Assume a barometric pressure
of 101 kPa and a specific gravity of 1.03 for seawater.
3–30 A gas is contained in a vertical, frictionless piston–cylinder device. The piston has a mass of 4 kg and a cross
sectional area of 35 cm2. A compressed spring above the piston exerts a force of 60 N on the piston. If the atmospheric
pressure is 95 kPa, determine the pressure inside the cylinder.
3–32 Both a gage and a manometer are attached to a gas tank to measure its pressure. If the reading on the pressure
gage is 65 kPa, determine the distance between the two fluid levels of the manometer if the fluid is (a) mercury
(ρ= 13,600 kg/m3) or (b) water (ρ= 1000 kg/m3).
3–35 The system shown in the figure is used to accurately measure the pressure changes when the pressure is
increased by ΔP in the water pipe. When Dh = 70 mm, what is the change in the pipe pressure?
3–45 Freshwater and seawater flowing in parallel horizontal pipelines are connected to each other by a double U-tube
manometer, as shown in Fig. P3–45. Determine the pressure difference between the two pipelines. Take the density of
seawater at that location to be ρ= 1035 kg/m3. Can the air column be ignored in the analysis?
2
3–51 Two water tanks are connected to each other through a mercury manometer with inclined tubes, as shown in Fig.
P3–51. If the pressure difference between the two tanks is 20 kPa, calculate a and θ.
3–54 Two chambers with the same fluid at their base are separated by a 30-cm-diameter piston whose weight is 25 N,
as shown in Fig. P3–54. Calculate the gage pressures in chambers A and B.
3–75 A 6-m-high, 5-m-wide rectangular plate blocks the end of a 5-m-deep freshwater channel, as shown in Fig. P3–
75. The plate is hinged about a horizontal axis along its upper edge through a point A and is restrained from opening
by a fixed ridge at point B. Determine the force exerted on the plate by the ridge.
3
3–79 A water trough of semicircular cross section of radius 0.6 m consists of two symmetric parts hinged to each other
at the bottom, as shown in Fig. P3–79. The two parts are held together by a cable and turnbuckle placed every 3 m along
the length of the trough. Calculate the tension in each cable when the trough is filled to the rim.
Try to solve the following Problems
1- A 6-in.-diameter piston is located within a cylinder which is connected to a 0.5-in

diameter inclined-tube manometer as shown in the below Fig. The fluid in the cylinder
and the manometer is oil (specific weight =59 lb/ft3). When a weight W is placed on
the top of the cylinder, the fluid level in the manometer tube rises from point (1) to (2).
How heavy is the weight? Assume that the change in position of the piston is negligible.
2. A gasoline line is connected to a pressure gage through a double-U manometer, as shown in

the following Fig. If the reading of the pressure gage is 370 kPa, determine the gage pressure
of the gasoline line.

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Chapter 3 Tutorial Problems

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Fluid Mechanics

Tutorial Problems Set 3

Try to solve the following Problems

1- A 6-in.-diameter piston is located within a cylinder which is connected to a 0.5-in

2. A gasoline line is connected to a pressure gage through a double-U manometer, as shown in

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