Thermo-Ch1 - 1-1 Chapter 1 INTRODUCTION AND BASIC CONCEPTS...

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1-1 Chapter 1 INTRODUCTION AND BASIC CONCEPTS Thermodynamics 1-1C Classical thermodynamics is based on experimental observations whereas statistical thermodynamics is based on the average behavior of large groups of particles. 1-2C On a downhill road the potential energy of the bicyclist is being converted to kinetic energy, and thus the bicyclist picks up speed. There is no creation of energy, and thus no violation of the conservation of energy principle. Mass, Force, and Units 1-5C Pound-mass lbm is the mass unit in English system whereas pound-force lbf is the force unit. One pound-force is the force required to accelerate a mass of 32.174 lbm by 1 ft/s 2 . In other words, the weight of a 1-lbm mass at sea level is 1 lbf. 1-6C In this unit, the word light refers to the speed of light. The light-year unit is then the product of a velocity and time. Hence, this product forms a distance dimension and unit. 1-7C There is no acceleration, thus the net force is zero in both cases.

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1-2 1-8E The weight of a man on earth is given. His weight on the moon is to be determined. Analysis Applying Newton's second law to the weight force gives lbm 4 . 180 lbf 1 ft/s lbm 174 . 32 ft/s 10 . 32 lbf 180 2 2 = = = → = g W m mg W Mass is invariant and the man will have the same mass on the moon. Then, his weight on the moon will be lbf 30.7 = = = 2 2 ft/s lbm 174 . 32 lbf 1 ) ft/s 47 . 5 )( lbm 4 . 180 ( mg W 1-10 The variation of gravitational acceleration above the sea level is given as a function of altitude. The height at which the weight of a body will decrease by 1% is to be determined. 0 z Analysis The weight of a body at the elevation z can be expressed as Wm gm z == − × (. . ) 9 807 332 10 6 In our case, WW m g m ss == = 0 99 0 99 0 99 9 807 .. . ( ) ( . ) Substituting, m 29,539 = × = z z ) 10 32 . 3 81 . 9 ( ) 81 . 9 ( 99 . 0 6 Sea level
1-3 1-12 The acceleration of an aircraft is given in g ’s. The net upward force acting on a man in the aircraft is to be determined. Analysis From the Newton's second law, the force applied is N 5297 = × = = = 2 2 m/s kg 1 N 1 ) m/s 9.81 kg)(6 (90 ) g 6 ( m ma F Systems, Properties, State, and Processes 1-16C This system is a region of space or open system in that mass such as air and food can cross its control boundary. The system can also interact with the surroundings by exchanging heat and work across its control boundary. By tracking these interactions, we can determine the energy conversion characteristics of this system. 1-17C The system is taken as the air contained in the piston-cylinder device. This system is a closed or fixed mass system since no mass enters or leaves it.

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This note was uploaded on 05/22/2008 for the course EGN 3343 taught by Professor Umitkursun during the Summer '08 term at University of Central Florida.

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Thermo-Ch1 - 1-1 Chapter 1 INTRODUCTION AND BASIC CONCEPTS...

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