Chapter 1 Getting Started steady wind,the turbine-generator is likely to reach steady-state operation, where the rotational speed of the blades is constant and a steady electric Skills Developed current is generated. Ability to. 1(b)In this case,the battery is studied as a closed system.The principal apply the problem-solving interaction between the system and its surroundings is the electric current methodology used in this passing into the battery through the wires.As noted in part (a),this inter- book. action is not considered a mass transfer.As the battery is charged and define a control volume and chemical reactions occur within it,the temperature of the battery surface identify interactions on its may become somewhat elevated and a thermal interaction might occur boundary. between the battery and its surroundings.This interaction is likely to be of define a closed system and secondary importance.Also,as the battery is charged,the state within identify interactions on its changes with time.The battery is not at steady state. boundary distinguish steady-state 1 Using terms familiar from a previous physics course,the system of part(a) operation from nonsteady operation involves the conversion of kinetic energy to electricity,whereas the system of part(b)involves energy storage within the battery. Quick Quiz May an overall system consisting of the turbine-generator and battery be considered as operating at steady state?Explain.Ans.No.A system is at steady state only if none of its properties changes with time. C CHAPTER SUMMARY AND STUDY GUIDE In this chapter,we have introduced some of the fundamental This book has several features that facilitate study and concepts and definitions used in the study of thermody- contribute to understanding.For an overview,see How to namics.The principles of thermodynamics are applied by Use This Book Effectively inside the front cover of the book. engineers to analyze and design a wide variety of devices The following checklist provides a study guide for this intended to meet human needs. chapter.When your study of the text and the end-of-chapter An important aspect of thermodynamic analysis is to iden- exercises has been completed you should be able to tify systems and to describe system behavior in terms of prop- c write out the meanings of the terms listed in the margin erties and processes.Three important properties discussed in this chapter are specific volume,pressure,and temperature. throughout the chapter and explain each of the related concepts.The subset of key concepts listed is particularly In thermodynamics,we consider systems at equilibrium important in subsequent chapters. states and systems undergoing processes(changes of state). We study processes during which the intervening states are c identify an appropriate system boundary and describe not equilibrium states and processes during which the the interactions between the system and its surroundings. departure from equilibrium is negligible. c work on a molar basis using Eq.1.8. In this chapter,we have introduced SI and English Engineer- c use SI and English units for mass,length,time,force,and ing units for mass,length,time,force,and temperature.You will temperature and apply appropriately Newton's second need to be familiar with both sets of units as you use this book. law and Eqs.1.16-1.19. For Conversion Factors,see inside the front cover of the book. Chapter 1 concludes with discussions of how thermody- c apply the methodology for problem solving discussed in namics is used in engineering design and how to solve ther- Sec.1.9. modynamics problems systematically. C KEY ENGINEERING CONCEPTS system,p. state,p. pressure,p. surroundings,p. process,p. temperature,p. boundary,p. extensive property,p. Kelvin scale,p. closed system,p. intensive property,p. Rankine scale,p. control volume,p. equilibrium,p. property,p. specific volume,p
26 Chapter 1 Getting Started steady wind, the turbine–generator is likely to reach steady-state operation, where the rotational speed of the blades is constant and a steady electric current is generated. ❶ (b) In this case, the battery is studied as a closed system. The principal interaction between the system and its surroundings is the electric current passing into the battery through the wires. As noted in part (a), this interaction is not considered a mass transfer. As the battery is charged and chemical reactions occur within it, the temperature of the battery surface may become somewhat elevated and a thermal interaction might occur between the battery and its surroundings. This interaction is likely to be of secondary importance. Also, as the battery is charged, the state within changes with time. The battery is not at steady state. ❶ Using terms familiar from a previous physics course, the system of part (a) involves the conversion of kinetic energy to electricity, whereas the system of part (b) involves energy storage within the battery. ✓Skills Developed Ability to… ❑ apply the problem-solving methodology used in this book. ❑ define a control volume and identify interactions on its boundary. ❑ define a closed system and identify interactions on its boundary. ❑ distinguish steady-state operation from nonsteady operation. May an overall system consisting of the turbine–generator and battery be considered as operating at steady state? Explain. Ans. No. A system is at steady state only if none of its properties changes with time. Quick Quiz In this chapter, we have introduced some of the fundamental concepts and definitions used in the study of thermodynamics. The principles of thermodynamics are applied by engineers to analyze and design a wide variety of devices intended to meet human needs. An important aspect of thermodynamic analysis is to identify systems and to describe system behavior in terms of properties and processes. Three important properties discussed in this chapter are specific volume, pressure, and temperature. In thermodynamics, we consider systems at equilibrium states and systems undergoing processes (changes of state). We study processes during which the intervening states are not equilibrium states and processes during which the departure from equilibrium is negligible. In this chapter, we have introduced SI and English Engineering units for mass, length, time, force, and temperature. You will need to be familiar with both sets of units as you use this book. For Conversion Factors, see inside the front cover of the book. Chapter 1 concludes with discussions of how thermodynamics is used in engineering design and how to solve thermodynamics problems systematically. This book has several features that facilitate study and contribute to understanding. For an overview, see How to Use This Book Effectively inside the front cover of the book. The following checklist provides a study guide for this chapter. When your study of the text and the end-of-chapter exercises has been completed you should be able to c write out the meanings of the terms listed in the margin throughout the chapter and explain each of the related concepts. The subset of key concepts listed is particularly important in subsequent chapters. c identify an appropriate system boundary and describe the interactions between the system and its surroundings. c work on a molar basis using Eq. 1.8. c use SI and English units for mass, length, time, force, and temperature and apply appropriately Newton’s second law and Eqs. 1.16–1.19. c apply the methodology for problem solving discussed in Sec. 1.9. c CHAPTER SUMMARY AND STUDY GUIDE c KEY ENGINEERING CONCEPTS system, p. 4 surroundings, p. 4 boundary, p. 4 closed system, p. 6 control volume, p. 6 property, p. 9 state, p. 9 process, p. 9 extensive property, p. 9 intensive property, p. 9 equilibrium, p. 10 specific volume, p. 14 pressure, p. 14 temperature, p. 19 Kelvin scale, p. 21 Rankine scale, p. 21
Chapter 1 Getting Started 11.A special type of closed system that does not interact in (c)none of its properties changes with time or with location any way with its surroundings is an_ within the system. 12.Describe the difference between specific volume expressed (d)none of the above. on a mass basis and a molar basis 22.A system having a mass of 1500 Ib undergoes a process in 13.A system is said to be at if none of its which its elevation relative to Earth's surface increases by properties changes with time. 500 ft.If the local acceleration of gravity at its final state is g =30.0 ft/s2,the weight of the system at that state is 14.A control volume is a system that lbf. (a)always contains the same matter. 23.Classify items a through g shown on the pressure-specific (b)allows a transfer of matter across its boundary. volume diagram in Fig.P1.23C as a property,a state,or a (c)does not interact in any way with its surroundings process. (d)always has a constant volume. 15.What is the objective of an engineering model in therm- odynamic analysis? 16. is pressure with respect to the zero pressure of a complete vacuum. a P2 17.A gas contained within a piston-cylinder assembly undergoes Process 1-2-3 shown on the pressure-volume d pi diagram in Fig.P1.17C.Process 1-2-3 is 2 1 8 Fig.P. 24.When a system is isolated, (a)its mass remains constant. (b)its temperature may change. (c)its pressure may change. (d)all of the above. 25.The resultant pressure force acting on a body completely Fig.P.C or partially submerged in a liquid is the 26.The list consisting only of intensive properties is (a)a constant-volume process followed by constant-pressure (a)volume,temperature,pressure. compression (b)specific volume,mass,volume. (b)constant-pressure compression followed by a constant- volume process. (c)pressure,temperature,specific volume. (d)mass,temperature,pressure. (c)a constant-volume process followed by a constant- pressure expansion. (d)constant-pressure expansion followed by a constant- Indicate whether the following statements are true or false. volume process. Explain. 18.The statement,"When two objects are in thermalequilibrium 27.Gage pressure indicates the difference between the absolute with a third object,they are in thermal equilibrium with each pressure of a system and the absolute pressure of the other,”is called the_ atmosphere existing outside the measuring device. 19.SI base units include 28.Systems can be studied only from a macroscopic point of view. (a)kilogram (kg),meter (m),newton (N). (b)kelvin (K),meter (m),second (s). 29.Kilogram,second,foot,and newton are all examples of SI units. (c)second (s),meter (m)pound mass. (d)kelvin (K),newton (N),second (s). 30.Temperature is an extensive property. 20.Explain why the value for gage pressure is always less than 31.Mass is an intensive property. the corresponding value for absolute pressure. 32.The value of the temperature expressed using the Celsius 21.A system is at steady state if temperature scale is always higher than its value expressed (a)none of its properties changes with time. using the Kelvin scale. (b)none of its properties changes with location within the 33.Intensive properties may be functions of both position and system. time,whereas extensive properties can vary only with time
28 Chapter 1 Getting Started 11. A special type of closed system that does not interact in any way with its surroundings is an ___________. 12. Describe the difference between specific volume expressed on a mass basis and a molar basis ____________. 13. A system is said to be at ____________ if none of its properties changes with time. 14. A control volume is a system that (a) always contains the same matter. (b) allows a transfer of matter across its boundary. (c) does not interact in any way with its surroundings. (d) always has a constant volume. 15. What is the objective of an engineering model in thermodynamic analysis? 16. ______________ is pressure with respect to the zero pressure of a complete vacuum. 17. A gas contained within a piston–cylinder assembly undergoes Process 1–2–3 shown on the pressure–volume diagram in Fig. P1.17C. Process 1–2–3 is (c) none of its properties changes with time or with location within the system. (d) none of the above. 22. A system having a mass of 1500 lb undergoes a process in which its elevation relative to Earth’s surface increases by 500 ft. If the local acceleration of gravity at its final state is g 5 30.0 ft/s2 , the weight of the system at that state is ___________ lbf. 23. Classify items a through g shown on the pressure–specific volume diagram in Fig. P1.23C as a property, a state, or a process. 24. When a system is isolated, (a) its mass remains constant. (b) its temperature may change. (c) its pressure may change. (d) all of the above. 25. The resultant pressure force acting on a body completely or partially submerged in a liquid is the ____________. 26. The list consisting only of intensive properties is (a) volume, temperature, pressure. (b) specific volume, mass, volume. (c) pressure, temperature, specific volume. (d) mass, temperature, pressure. Indicate whether the following statements are true or false. Explain. 27. Gage pressure indicates the difference between the absolute pressure of a system and the absolute pressure of the atmosphere existing outside the measuring device. 28. Systems can be studied only from a macroscopic point of view. 29. Kilogram, second, foot, and newton are all examples of SI units. 30. Temperature is an extensive property. 31. Mass is an intensive property. 32. The value of the temperature expressed using the Celsius temperature scale is always higher than its value expressed using the Kelvin scale. 33. Intensive properties may be functions of both position and time, whereas extensive properties can vary only with time. V p 1 2 3 Fig. P1.17C (a) a constant-volume process followed by constant-pressure compression. (b) constant-pressure compression followed by a constantvolume process. (c) a constant-volume process followed by a constantpressure expansion. (d) constant-pressure expansion followed by a constantvolume process. 18. The statement, “When two objects are in thermal equilibrium with a third object, they are in thermal equilibrium with each other,” is called the _______________. 19. SI base units include (a) kilogram (kg), meter (m), newton (N). (b) kelvin (K), meter (m), second (s). (c) second (s), meter (m) pound mass. (d) kelvin (K), newton (N), second (s). 20. Explain why the value for gage pressure is always less than the corresponding value for absolute pressure. 21. A system is at steady state if (a) none of its properties changes with time. (b) none of its properties changes with location within the system. 1 2 p p2 1 e c b a d p1 f g v2 vv Fig.P1.23C
0T0m00D00D0000T00I00m0m00 34.Devices that measure pressure include barometers,47.1 N equals 1 kg.m/s2 but 1 Ibf does not equal 1 lb.ft/s2. Bourdon tube gages,and manometers. 48.A vessel holding 0.5 kg of oxygen (O2)contains 16 lb of 35.Both the Kelvin scale and the Rankine scale are absolute 02. temperature scales. 49.Specific volume.the volume per unit of mass,is an intensive 36.If a system is isolated from its surroundings and no changes property whereas volume and mass are extensive properties. occur in its observable properties,the system was in 50.In local surroundings at standard atmospheric pressure,a equilibrium at the moment it was isolated. gage will indicate a pressure of 0.2 atm for a refrigerant 37.The specific volume is the reciprocal of the density. whose absolute pressure is 1.2 atm. 38.Volume is an extensive property. 51.The kilogram for mass and the meter for length are 39.The pound force,Ibf,is equal to the pound mass,Ib. examples of SI base units defined relative to fabricated objects. 40.The value of a temperature expressed using the Rankine scale is always higher than its value expressed using the 52.The Rankine degree is a smaller temperature unit than the Fahrenheit temperature scale. Kelvin degree. 41.Pressure is an intensive property. 53.If the value of any property of a system changes with time, that system cannot be at steady state. 42.A closed system always contains the same matter;there is no transfer of matter across its boundary 54.According to Archimedes'principle,the magnitude of the buoyant force acting on a submerged body is equal to the 43.One nanosecond equals 10 seconds. weight of the body. 44.A control volume is a special type of closed system that 55.The composition of a closed system cannot change. does not interact in any way with its surroundings. 56.Temperature is the property that is the same for each of 45.When a closed system undergoes a process between two two systems when they are in thermal equilibrium. specified states,the change in temperature between the end states is independent of details of the process. 57.The volume of a closed system can change. 46.Body organs,such as the human heart,whose shapes 58.The pressure unit psia indicates an absolute pressure change as they perform their normal functions can be expressed in pounds force per square inch. studied as control volumes. PROBLEMS:DEVELOPING ENGINEERING SKILLS Exploring System Concepts 1.1 Using the Internet,obtain information about the operation of an application listed or shown in Table 1.1.Obtain sufficient information to provide a full description of the application,together with relevant thermodynamic aspects. Present your findings in a memorandum. Hot 1.2 As illustrated in Fig.P1.2,water circulates through a piping Shower system,servicing various household needs.Considering the Dishwasher water heater as a system,identify locations on the system boundary where the system interacts with its surroundings and describe significant occurrences within the system. Repeat for the dishwasher and for the shower.Present your findings in a memorandum. Cold Water Hot water 1.3 Many public memorials and community landmarks include meter heater water features such as waterfalls,fountains,reflecting pools, Electric meter and so on.as part of the design.Select one such memorial or landmark.Using the Internet research the history and -Drain lines overall design features of your selection.Identify an appropriate boundary for the water,and determine whether the water should be treated as a closed system or a control volume.Describe any devices required to achieve the water Fig.P. effect and to maintain appropriate water quality.Prepare a 5-minute PowerPoint presentation summarizing your research to present to your class
Problems: Developing Engineering Skills 29 34. Devices that measure pressure include barometers, Bourdon tube gages, and manometers. 35. Both the Kelvin scale and the Rankine scale are absolute temperature scales. 36. If a system is isolated from its surroundings and no changes occur in its observable properties, the system was in equilibrium at the moment it was isolated. 37. The specific volume is the reciprocal of the density. 38. Volume is an extensive property. 39. The pound force, lbf, is equal to the pound mass, lb. 40. The value of a temperature expressed using the Rankine scale is always higher than its value expressed using the Fahrenheit temperature scale. 41. Pressure is an intensive property. 42. A closed system always contains the same matter; there is no transfer of matter across its boundary. 43. One nanosecond equals 109 seconds. 44. A control volume is a special type of closed system that does not interact in any way with its surroundings. 45. When a closed system undergoes a process between two specified states, the change in temperature between the end states is independent of details of the process. 46. Body organs, such as the human heart, whose shapes change as they perform their normal functions can be studied as control volumes. 47. 1 N equals 1 kg ? m/s2 but 1 lbf does not equal 1 lb ? ft/s2 . 48. A vessel holding 0.5 kg of oxygen (O2) contains 16 lb of O2. 49. Specific volume, the volume per unit of mass, is an intensive property whereas volume and mass are extensive properties. 50. In local surroundings at standard atmospheric pressure, a gage will indicate a pressure of 0.2 atm for a refrigerant whose absolute pressure is 1.2 atm. 51. The kilogram for mass and the meter for length are examples of SI base units defined relative to fabricated objects. 52. The Rankine degree is a smaller temperature unit than the Kelvin degree. 53. If the value of any property of a system changes with time, that system cannot be at steady state. 54. According to Archimedes’ principle, the magnitude of the buoyant force acting on a submerged body is equal to the weight of the body. 55. The composition of a closed system cannot change. 56. Temperature is the property that is the same for each of two systems when they are in thermal equilibrium. 57. The volume of a closed system can change. 58. The pressure unit psia indicates an absolute pressure expressed in pounds force per square inch. Exploring System Concepts 1.1 Using the Internet, obtain information about the operation of an application listed or shown in Table 1.1. Obtain sufficient information to provide a full description of the application, together with relevant thermodynamic aspects. Present your findings in a memorandum. 1.2 As illustrated in Fig. P1.2, water circulates through a piping system, servicing various household needs. Considering the water heater as a system, identify locations on the system boundary where the system interacts with its surroundings and describe significant occurrences within the system. Repeat for the dishwasher and for the shower. Present your findings in a memorandum. 1.3 Many public memorials and community landmarks include water features such as waterfalls, fountains, reflecting pools, and so on, as part of the design. Select one such memorial or landmark. Using the Internet research the history and overall design features of your selection. Identify an appropriate boundary for the water, and determine whether the water should be treated as a closed system or a control volume. Describe any devices required to achieve the water effect and to maintain appropriate water quality. Prepare a 5-minute PowerPoint presentation summarizing your research to present to your class. c PROBLEMS: DEVELOPING ENGINEERING SKILLS Water meter Cold Drain lines Hot water heater Hot Dishwasher Shower Electric meter + – + – Fig. P1.2
Chapter 1 Getting Started Working with Units 1.13 At a certain elevation,the pilot of a balloon has a mass 1.4 Perform the following unit conversions: of 120 lb and a weight of 119 lbf.What is the local acceleration of gravity,in ft/s,at that elevation?If the balloon drifts to (a)1 L to in.3 another elevation where g =32.05 ft/s2,what is her weight, (b)650 J to Btu in lbf,and mass,in Ib? (c)0.135 kW to ft·1bfs 1.14 Estimate the magnitude of the force,in lbf,exerted on a (d)378 g/s to Ib/min (e)304 kPa to lbf/in.2 12-lb goose in a collision of duration 10s with an airplane (f)55 m'/h to ft'/s taking off at 150 miles/h. (g)50 km/h to ft/s 1.15 Determine the upward applied force,in Ibf,required to (h)8896 N to ton(=20001bf) accelerate a 4.5-lb model rocket vertically upward,as shown 1.5 Perform the following unit conversions: in Fig.P1.15,with an acceleration of 3 g's.The only other significant force acting on the rocket is gravity,and 1 g (a)122 in.3 to L 32.2ft/s2. (b)778.17ft·1 bf to kJ (c)100 hp to kW (d)1000 1b/h to kg/s (e)29.392 Ibf/in.2 to bar (f)2500 ft'/min to m'/s m=4.5 lb (g)75 mile/h to km/h a=3g (h)1 ton (=2000 lbf)to N 1.6 Which of the following food items weighs approximately 1 newton? a.a grain of rice b.a small strawberry c.a medium-sized apple d.a large watermelon Working with Force and Mass 1.7 A person whose mass is 150 lb weighs 144.4 lbf.Determine (a)the local acceleration of gravity,in ft/s",and (b)the person's mass,in Ib,and weight,in Ibf,if g 32.174 ft/s2. 1.8 The Phoenix with a mass of 350 kg was a spacecraft used for exploration of Mars.Determine the weight of the Phoenix,in N,(a)on the surface of Mars where the acceleration of gravity is 3.73 m/s2 and(b)on Earth where the acceleration of gravity is 9.81 m/s2. 1.9 Atomic and molecular weights of some common substances are listed in Appendix Tables A-1 and A-1E.Using data from the appropriate table,determine Fig.P. (a)the mass,in kg,of 20 kmol of each of the following:air,1.16 An object is subjected to an applied upward force of C.H,O,CO,. 10 lbf.The only other force acting on the object is the force (b)the number of Ibmol in 50 lb of each of the following: of gravity.The acceleration of gravity is 32.2 ft/s2.If the H2,N2.NH3.C3Hg. object has a mass of 50 lb,determine the net acceleration of 1.10 In severe head-on automobile accidents,a deceleration of the object,in ft/s2.Is the net acceleration upward or downward? 60 g's or more (1 g =32.2 ft/s)often results in a fatality. 1.17 A communications satellite weighs 4400 N on Earth What force,in Ibf,acts on a child whose mass is 50 lb,when where g=9.81 m/s2.What is the weight of the satellite,in subjected to a deceleration of 60 g's? N.as it orbits Earth where the acceleration of gravity is 0.224 1.11 At the grocery store you place a pumpkin with a mass of m/s2?Express each weight in Ibf. 12.5 Ib on the produce spring scale.The spring in the scale 1.18 Using local acceleration of gravity data from the Internet, operates such that for each 4.7 Ibf applied,the spring determine the weight,in N,of a person whose mass is 80 kg elongates one inch.If local acceleration of gravity is 32.2 ft/s2, living in: what distance,in inches,did the spring elongate? (a)Mexico City,Mexico 1.12 A spring compresses in length by 0.14 in.for every 1 Ibf (b)Cape Town,South Africa of applied force.Determine the mass of an object,in pounds (c)Tokyo,Japan mass,that causes a spring deflection of 1.8 in.The local (d)Chicago,IL acceleration of gravity =31 ft/s2. (e)Copenhagen,Denmark
30 Chapter 1 Getting Started Working with Units 1.4 Perform the following unit conversions: (a) 1 L to in.3 (b) 650 J to Btu (c) 0.135 kW to ft ? lbf/s (d) 378 g/s to lb/min (e) 304 kPa to lbf/in.2 (f) 55 m3 /h to ft3 /s (g) 50 km/h to ft/s (h) 8896 N to ton (52000 lbf) 1.5 Perform the following unit conversions: (a) 122 in.3 to L (b) 778.17 ft ? lbf to kJ (c) 100 hp to kW (d) 1000 lb/h to kg/s (e) 29.392 lbf/in.2 to bar (f) 2500 ft3 /min to m3 /s (g) 75 mile/h to km/h (h) 1 ton (52000 lbf) to N 1.6 Which of the following food items weighs approximately 1 newton? a. a grain of rice b. a small strawberry c. a medium-sized apple d. a large watermelon Working with Force and Mass 1.7 A person whose mass is 150 lb weighs 144.4 lbf. Determine (a) the local acceleration of gravity, in ft/s2 , and (b) the person’s mass, in lb, and weight, in lbf, if g 5 32.174 ft/s2 . 1.8 The Phoenix with a mass of 350 kg was a spacecraft used for exploration of Mars. Determine the weight of the Phoenix, in N, (a) on the surface of Mars where the acceleration of gravity is 3.73 m/s2 and (b) on Earth where the acceleration of gravity is 9.81 m/s2 . 1.9 Atomic and molecular weights of some common substances are listed in Appendix Tables A-1 and A-1E. Using data from the appropriate table, determine (a) the mass, in kg, of 20 kmol of each of the following: air, C, H2O, CO2. (b) the number of lbmol in 50 lb of each of the following: H2, N2, NH3, C3H8. 1.10 In severe head-on automobile accidents, a deceleration of 60 g’s or more (1 g 5 32.2 ft/s2 ) often results in a fatality. What force, in lbf, acts on a child whose mass is 50 lb, when subjected to a deceleration of 60 g’s? 1.11 At the grocery store you place a pumpkin with a mass of 12.5 lb on the produce spring scale. The spring in the scale operates such that for each 4.7 lbf applied, the spring elongates one inch. If local acceleration of gravity is 32.2 ft/s2 , what distance, in inches, did the spring elongate? 1.12 A spring compresses in length by 0.14 in. for every 1 lbf of applied force. Determine the mass of an object, in pounds mass, that causes a spring deflection of 1.8 in. The local acceleration of gravity 5 31 ft/s2 . 1.13 At a certain elevation, the pilot of a balloon has a mass of 120 lb and a weight of 119 lbf. What is the local acceleration of gravity, in ft/s2 , at that elevation? If the balloon drifts to another elevation where g 5 32.05 ft/s2 , what is her weight, in lbf, and mass, in lb? 1.14 Estimate the magnitude of the force, in lbf, exerted on a 12-lb goose in a collision of duration 10−3 s with an airplane taking off at 150 miles/h. 1.15 Determine the upward applied force, in lbf, required to accelerate a 4.5-lb model rocket vertically upward, as shown in Fig. P1.15, with an acceleration of 3 g’s. The only other significant force acting on the rocket is gravity, and 1 g 5 32.2 ft/s2 . m = 4.5 lb a = 3g Fig. P1.15 1.16 An object is subjected to an applied upward force of 10 lbf. The only other force acting on the object is the force of gravity. The acceleration of gravity is 32.2 ft/s2 . If the object has a mass of 50 lb, determine the net acceleration of the object, in ft/s2 . Is the net acceleration upward or downward? 1.17 A communications satellite weighs 4400 N on Earth where g 5 9.81 m/s2 . What is the weight of the satellite, in N, as it orbits Earth where the acceleration of gravity is 0.224 m/s2 ? Express each weight in lbf. 1.18 Using local acceleration of gravity data from the Internet, determine the weight, in N, of a person whose mass is 80 kg living in: (a) Mexico City, Mexico (b) Cape Town, South Africa (c) Tokyo, Japan (d) Chicago, IL (e) Copenhagen, Denmark