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engineering
mechanical engineering
Thermodynamics An Engineering Approach 8th edition Yunus A. Cengel, Michael A. Boles - Solutions
An office worker claims that a cup of cold coffee on his table warmed up to 80°C by picking up energy from the surrounding air, which is at 25°C. Is there any truth to his claim? Does this process violate any thermodynamic laws?
What is the difference between pound-mass and pound-force?
What is the difference between kg-mass and kg force?
What is the net force acting on a car cruising at a constant velocity of 70 km/h (a) On a level road and (b) On an uphill road?
A 3-kg plastic tank that has a volume of 0.2 m3 is filled with liquid water. Assuming the density of water is 1000 kg/m3, determine the weight of the combined system.
Determine the mass and the weight of the air contained in a room whose dimensions are 6 m x 6 m x 8 m. Assume the density of the air is 1.16 kg/m3. Answers: 334.1 kg, 3277 N
At 45° latitude, the gravitational acceleration as a function of elevation z above sea level is given by g = a - bz, where a = 9.807 m/s2 and b = 3.32 x 10-6 s-2. Determine the height above sea level where the weight of an object will decrease by 1 percent. Answer: 29,539 m
A 150-lbm astronaut took his bathroom scale (a spring scale) and a beam scale (compares masses) to the moon where the local gravity is g = 5.48 ft/s2. Determine how much he will weigh (a) On the spring scale and (b) On the beam scale. Answers: (a) 25.5 lbf; (b) 150 lbf
The acceleration of high-speed aircraft is sometimes expressed in g’s (in multiples of the standard acceleration of gravity). Determine the upward force, in N, that a 90-kg man would experience in an aircraft whose acceleration is 6 g’s.
A 5-kg rock is thrown upward with a force of 150 N at a location where the local gravitational acceleration is 9.79 m/s2. Determine the acceleration of the rock, in m/s2.
Solve Prob. 1–12 using EES (or other) software. Print out the entire solution, including the numerical results with proper units.
The value of the gravitational acceleration g decreases with elevation from 9.807 m/s2 at sea level to 9.767 m/s2 at an altitude of 13,000 m, where large passenger planes cruise. Determine the percent reduction in the weight of an airplane cruising at 13,000 m relative to its weight at sea level.
A large fraction of the thermal energy generated in the engine of a car is rejected to the air by the radiator through the circulating water. Should the radiator be analyzed as a closed system or as an open system? Explain.
A can of soft drink at room temperature is put into the refrigerator so that it will cool. Would you model the can of soft drink as a closed system or as an open system? Explain.
What is the difference between intensive and extensive properties?
For a system to be in thermodynamic equilibrium, do the temperature and the pressure have to be the same everywhere?
What is a quasi-equilibrium process? What is its importance in engineering?
Define the isothermal, isobaric, and isochoric processes.
What is the state postulate?
Is the state of the air in an isolated room completely specified by the temperature and the pressure? Explain.
What is a steady-flow process?
What is specific gravity? How is it related to density?
The density of atmospheric air varies with elevation, decreasing with increasing altitude. (a) Using the data given in the table, obtain a relation for the variation of density with elevation, and calculate the density at an elevation of 7000 m.(b) Calculate the mass of the atmosphere using the
What is the zeroth law of thermodynamics?
What are the ordinary and absolute temperature scales in the SI and the English system?
Consider an alcohol and a mercury thermometer that read exactly 0°C at the ice point and 100°C at the steam point. The distance between the two points is divided into 100 equal parts in both thermometers. Do you think these thermometers will give exactly the same reading at a temperature of, say,
The deep body temperature of a healthy person is 37°C. What is it in kelvins?
Consider a system whose temperature is 18°C. Express this temperature in R, K, and °F.
The temperature of a system rises by 15°C during a heating process. Express this rise in temperature in kelvins.
The temperature of a system drops by 45°F during a cooling process. Express this drop in temperature in K, R, and °C.
Consider two closed systems A and B. System A contains 3000 kJ of thermal energy at 20°C, whereas system B contains 200 kJ of thermal energy at 50°C. Now the systems are brought into contact with each other. Determine the direction of any heat transfer between the two systems.
What is the difference between gage pressure and absolute pressure?
Explain why some people experience nose bleeding and some others experience shortness of breath at high elevations.
Someone claims that the absolute pressure in a liquid of constant density doubles when the depth is doubled. Do you agree? Explain.
A tiny steel cube is suspended in water by a string. If the lengths of the sides of the cube are very small, how would you compare the magnitudes of the pressures on the top, bottom, and side surfaces of the cube?
Express Pascal’s law, and give a real-world example of it.
Consider two identical fans, one at sea level and the other on top of a high mountain, running at identical speeds. How would you compare (a) the volume flow rates and (b) the mass flow rates of these two fans?
A vacuum gage connected to a chamber reads 35 kPa at a location where the atmospheric pressure is 92 kPa. Determine the absolute pressure in the chamber.
A manometer is used to measure the air pressure in a tank. The fluid used has a specific gravity of 1.25, and the differential height between the two arms of the manometer is 28 in. If the local atmospheric pressure is 12.7 psia, determine the absolute pressure in the tank for the cases of the
The water in a tank is pressurized by air, and the pressure is measured by a multi fluid manometer as shown in Fig. P1–42 Determine the gage pressure of air in the tank if h1 = 0.2 m, h2 = 0.3 m, and h3 = 0.46 m. Take the densities of water, oil, and mercury to be 1000 kg/m3, 850 kg/m3, and
Determine the atmospheric pressure at a location where the barometric reading is 750 mm Hg. Take the density of mercury to be 13,600 kg/m3.
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 9 m.
The absolute pressure in water at a depth of 5 m is read to be 145 kPa. Determine (a) The local atmospheric pressure, and (b) The absolute pressure at a depth of 5 m in a liquid whose specific gravity is 0.85 at the same location.
Show that 1 kgf/cm2 = 14.223 psi.
A 200-pound man has a total foot imprint area of 72 in2. Determine the pressure this man exerts on the ground if (a) He stands on both feet and (b) He stands on one foot.
Consider a 70-kg woman who has a total foot imprint area of 400 cm2. She wishes to walk on the snow, but the snow cannot withstand pressures greater than 0.5 kPa. Determine the minimum size of the snowshoes needed (imprint area per shoe) to enable her to walk on the snow without sinking.
A vacuum gage connected to a tank reads 15 kPa at a location where the barometric reading is 750 mm Hg. Determine the absolute pressure in the tank. Take pHg = 13,590 kg/m3.
A pressure gage connected to a tank reads 50 psi at a location where the barometric reading is 29.1 mm Hg. Determine the absolute pressure in the tank. Take rHg = 848.4 lbm/ft3.
A pressure gage connected to a tank reads 500 kPa at a location where the atmospheric pressure is 94 kPa. Determine the absolute pressure in the tank.
The barometer of a mountain hiker reads 930 m bars at the beginning of a hiking trip and 780 m bars at the end. Neglecting the effect of altitude on local gravitational acceleration, determine the vertical distance climbed. Assume an average air density of 1.20 kg/m3.
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 mm Hg, respectively, determine the height of the building. Take the densities of air and mercury to be 1.18 kg/m3 and 13,600 kg/m3, respectively.
Solve Prob. 1€“53 using EES (or other) software. Print out the entire solution, including the numerical results with proper units.
Determine the pressure exerted on a diver at 30 m below the free surface of the sea. Assume a barometric pressure of 101 kPa and a specific gravity of 1.03 for seawater.
Determine the pressure exerted on the surface of a submarine cruising 175 ft below the free surface of the sea. Assume that the barometric pressure is 14.7 psia and the specific gravity of seawater is 1.03.
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.
Reconsider Prob. 1–57. Using EES (or other) software, investigate the effect of the spring force in the range of 0 to 500 N on the pressure inside the cylinder. Plot the pressure against the spring force, and discuss the results.
Both a gage and a manometer are attached to a gas tank to measure its pressure. If the reading on the pressure gage is 80 kPa, determine the distance between the two fluid levels of the manometer if the fluid is (a) Mercury (r = 13,600 kg/m3) or (b) Water (r = 1000 kg/m3).
Reconsider Prob. 1€“59. Using EES (or other) software, investigate the effect of the manometer fluid density in the range of 800 to 13,000 kg/m3 on the differential fluid height of the manometer. Plot the differential fluid height against the density, and discuss the results.
A manometer containing oil (r = 850 kg/m3) is attached to a tank filled with air. If the oil-level difference between the two columns is 60 cm and the atmospheric pressure is 98 kPa, determine the absolute pressure of the air in the tank.
A mercury manometer (r = 13,600 kg/m3) is connected to an air duct to measure the pressure inside. The difference in the manometer levels is 15 mm, and the atmospheric pressure is 100 kPa. (a) Judging from Fig. P1–62, determine if the pressure in the duct is above or below the atmospheric
Repeat Prob. 1–62 for a differential mercury height of 45 mm.
Blood pressure is usually measured by wrapping a closed air-filled jacket equipped with a pressure gage around the upper arm of a person at the level of the heart. Using a mercury manometer and a stethoscope, the systolic pressure (the maximum pressure when the heart is pumping) and the diastolic
The maximum blood pressure in the upper arm of a healthy person is about 120 mm Hg. If a vertical tube open to the atmosphere is connected to the vein in the arm of the person, determine how high the blood will rise in the tube. Take the density of the blood to be 1050 kg/m3.
Consider a 1.8-m-tall man standing vertically in water and completely submerged in a pool. Determine the difference between the pressures acting at the head and at the toes of this man, in kPa.
Consider a U-tube whose arms are open to the atmosphere. Now water is poured into the U-tube from one arm, and light oil (r = 790 kg/m3) from the other. One arm contains 70-cm-high water, while the other arm contains both fluids with an oil-to-water height ratio of 4. Determine the height of each
The hydraulic lift in a car repair shop has an output diameter of 30 cm and is to lift cars up to 2000 kg. Determine the fluid gage pressure that must be maintained in the reservoir.
Freshwater and seawater flowing in parallel horizontal pipelines are connected to each other by a double U-tube manometer, as shown in Fig. P1–69, determine the pressure difference between the two pipelines. Take the density of seawater at that location to be r = 1035 kg/m3. Can the air column be
Repeat Prob. 1–69 by replacing the air with oil whose specific gravity is 0.72.
The pressure in a natural gas pipeline is measured by the manometer shown in Fig. P1–71E with one of the arms open to the atmosphere where the local atmospheric pressure is 14.2 psia. Determine the absolute pressure in the pipeline.
Repeat Prob. 1€“71E by replacing air by oil with a specific gravity of 0.69.
The gage pressure of the air in the tank shown in Fig P1€“73 is measured to be 80 kPa. Determine the differential height h of the mercury column.
Repeat Prob. 1–73 for a gage pressure of 40 kPa.
The top part of a water tank is divided into two compartments, as shown in Fig. P1–75, now a fluid with an unknown density is poured into one side and the water level rise a certain amount on the other side to compensate for this effect. Based on the final fluid heights shown on the figure,
Consider a double-fluid manometer attached to an air pipe shown in Fig. P1–76, if the specific gravity of one fluid is 13.55 determines the specific gravity of the other fluid for the indicated absolute pressure of air. Take the atmospheric pressure to be 100 kPa
Consider the system shown in Fig. P1€“77, if a change of 0.7 kPa in the pressure of air causes the brine€“mercury interface in the right column to drop by 5 mm in the brine level in the right column while the pressure in the brine pipe remains constant, determine the ratio of
A multi fluid container is connected to a U-tube, as shown in Fig. P1–78, for the given specific gravities and fluid column heights, determine the gage pressure at A. Also determine the height of a mercury column that would create the same pressure at A.
What is the value of the engineering software packages in? (a) Engineering education and (b) Engineering practice?
Determine a positive real root of this equation using EES: 2x3 – 10x0.5 – 3x – 3
Solve this system of two equations with two unknowns EES: x3 – y2 = 7.75 3xy + y2 = 3.5
Solve this system of three equations with three unknowns using EES: 2x – y + z = 5 3x2 + 2y = z + 5 Xy + 2z = 8
Solve this system of three equations with three unknowns using EES: x2y – z = 1 x - 3y05 + xz = -5 x + y - z = 2
Specific heat is defined as the amount of energy needed to increase the temperature of a unit mass of a substance by one degree. The specific heat of water at room temperature is 4.18 kJ/kg · °C in SI unit system. Using the unit conversion function capability of EES, express the specific heat
A hydraulic lift is to be used to lift a 2500 kg weight by putting a weight of 25 kg on a piston with a diameter of 10 cm. Determine the diameter of the piston on which the weight is to be placed.
A vertical piston€“cylinder device contains a gas at a pressure of 100 kPa. The piston has a mass of 5 kg and a diameter of 12 cm. Pressure of the gas is to be increased by placing some weights on the piston. Determine the local atmospheric pressure and the mass of the weights that will
The pilot of an airplane reads the altitude 3000 m and the absolute pressure 58 kPa when flying over a city. Calculate the local atmospheric pressure in that city in kPa and in mm Hg. Take the densities of air and mercury to be 1.15 kg/m3 and 13,600 kg/m3, respectively.
The weight of bodies may change somewhat from one location to another as a result of the variation of the gravitational acceleration g with elevation. Accounting for this variation using the relation in Prob. 1–9, determine the weight of an 80-kg person at sea level (z = 0), in Denver (z = 1610
A man goes to a traditional market to buy a steak for dinner. He finds a 12-oz steak (1 lbm = 16 oz) for $3.15. He then goes to the adjacent international market and finds a 320-g steak of identical quality for $2.80. Which steak is the better buy?
The reactive force developed by a jet engine to push an airplane forward is called thrust, and the thrust developed by the engine of a Boeing 777 is about 85,000 lbf. Express this thrust in N and kgf.
The efficiency of a refrigerator increases by 3 percent for each °C rise in the minimum temperature in the device. What is the increase in the efficiency for each? (a) K, (b) °F, and (c) R rise in temperature?
The boiling temperature of water decreases by about 3°C for each 1000-m rise in altitude. What is the decrease in the boiling temperature in (a) K, (b) °F, and (c) R for each 1000-m rise in altitude?
The average body temperature of a person rises by about 2°C during strenuous exercise. What is the rise in the body temperature in? (a) K, (b) °F, and (c) R during strenuous exercise?
Hyperthermia of 5°C (i.e., 5°C rise above the normal body temperature) is considered fatal. Express this fatal level of hyperthermia in (a) K, (b) °F, and (c) R.
A house is losing heat at a rate of 4500 kJ/h per °C temperature difference between the indoor and the outdoor temperatures. Express the rate of heat loss from this house per (a) K, (b) °F, and (c) R difference between the indoor and the outdoor temperature.
The average temperature of the atmosphere in the world is approximated as a function of altitude by the relation T atm = 288.15 - 6.5z where Tatm is the temperature of the atmosphere in K and z is the altitude in km with z = 0 at sea level. Determine the average temperature of the atmosphere
Joe Smith, an old-fashioned engineering student, believes that the boiling point of water is best suited for use as the reference point on temperature scales. Unhappy that the boiling point corresponds to some odd number in the current absolute temperature scales, he has proposed a new absolute
It is well-known that cold air feels much colder in windy weather than what the thermometer reading indicates because of the “chilling effect” of the wind. This effect is due to the increase in the convection heat transfer coefficient with increasing air velocities. The equivalent wind chill
Reconsider Problem 1–98E Using EES (or other) software, plot the equivalent wind chill temperatures in °F as a function of wind velocity in the range of 4 to 100 mph for the ambient temperatures of 20, 40, and 60°F. Discuss the results.
An air-conditioning system requires a 20-m-long section of 15-cm diameter duct work to be laid underwater. Determine the upward force the water will exert on the duct. Take the densities of air and water to be 1.3 kg/m3 and 1000 kg/m3, respectively.
Balloons are often filled with helium gas because it weighs only about one-seventh of what air weighs under identical conditions. The buoyancy force, which can be expressed as Fb = paiv gV balloon, will push the balloon upward. If the balloon has a diameter of 10 m and carries two people, 70 kg
Reconsider Prob. 1–101. Using EES (or other) software, investigate the effect of the number of people carried in the balloon on acceleration. Plot the acceleration against the number of people, and discuss the results.
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