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Matter and Energy

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Drill Answer the following: 1) List 3 types of energy: 2) List 2 types of work:

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Matter and Energy Thermodynamics - “the study of systems and energy transfer” On a day in January, a household digital thermometer gives a reading of 30 o C; what is the absolute temperature outside? Known: A thermometer reads 30 o C Find: Absolute temperature read by thermometer [K] Sketch: Assumptions: N/A Solution:

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Matter and Energy Thermodynamics - “the study of systems and energy transfer” A spherical balloon has a diameter of 3m. The air trapped inside has a specific volume of 0.94 m 3 /kg. Determine the weight of the air inside the balloon assuming the acceleration of gravity is 9.8 m/s 2. Known: A sphere is filled with air (D=3m, v = 0.94 m 3 /kg) Find: Weight of the air, [N] Sketch: Assumptions: Closed System, g = 9.8 m/s 2 Solution: D = 3m

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Matter & Energy Classwork A spherical balloon has a diameter of 5m. The air trapped inside has a specific volume of 0.84 m 3 /kg. Determine the weight of the air inside the balloon assuming the acceleration of gravity is 9.8 m/s 2. A manometer filled with water is used to measure the pressure of a gas in a tank. The water ( ρ = 1000 kg/m 3 ) is displaced by a height of 60 centimeter. What is the gage pressure of the gas in the tank? What is the absolute pressure? A vertical piston-cylinder device (D = 30 cm) contains a trapped mixture of gases. The piston (m = 0.5 kg) falls and compresses the gas mixture from 4 m 3 down to 1m 3. How much work is done by the piston on the gas mixture? A piston cylinder containing a gas is compressed. The work done by the system during expansion is 100 kJ and the change in energy of the system is 200 kJ. Find the magnitude and direction of any heat transfer associated with this process.

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Matter and Energy Thermodynamics - “the study of systems and energy transfer” A manometer filled with water is used to measure the pressure of a gas in a tank. The water ( ρ = 990 kg/m 3 ) is displaced by a height of meter. What is the gage pressure of the gas in the tank? What is the absolute pressure? Tank P atm Known: A water manometer measures gas pressure ( ρ = 990 kg/m 3 ), h = m Find: Pressure of gas in tank, P tank in Pa; Absolute pressure of gas in tank, P abs in Pa Sketch: Assumptions: P atm = kPa, P tank = P 1, g = 9.8 m/s 2 Solution: P tank = P 1 = ρgh P tank = ( 990 kg/m 3 )(9.8 m/s 2 )( m) P tank = Pa P abs = P tank + P atm = Pa kPa = kPa

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Matter and Energy Thermodynamics - “the study of systems and energy transfer” A vertical piston-cylinder device (D = 10 cm) contains a trapped mixture of gases. The piston (m = 3 kg) falls and compresses the gas mixture from 4 m 3 down to 1.2 m 3. How much work is done by the piston on the gas? Known: A gas mixture is compressed inside of a piston-cylinder Find: Work done by the piston, [kJ] Sketch: Assumptions: Closed System, Solution: In this case, the work is negative; that implies that this work is going into the system. vertical piston-cylinder Vertical-piston cylinder -> Isobaric

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Matter and Energy Thermodynamics - “the study of systems and energy transfer” A piston cylinder containing a gas is compressed. The work done on the system during compression is 60 kJ and the change in energy of the system is 300 kJ. Find the magnitude and direction of any heat transfer. Known: A gas is compressed inside of a piston-cylinder Find: Q, [kJ]; Direction of heat transfer Sketch: Assumptions: Closed System Solution: The work is going into the system, so we must give it a negative sign… The sign on the heat transfer is positive, so heat is flowing into the system.

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Matter and Energy Thermodynamics - “the study of systems and energy transfer” A vertical, piston cylinder containing a gas is allowed to expand from 1 m 3 to 3 m 3. The heat added to the system during the expansion was 200 kJ and the change in energy of the system is 340 kJ. Find the gas pressure, in kPa. Known: A gas expands inside a vertical piston-cylinder; E=340 kJ; Q = 200kJ Find: P, [kPa] Sketch: Assumptions: Closed System, Isobaric Solution:

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Matter and Energy Thermodynamics - “the study of systems and energy transfer” A vertical, piston cylinder containing a gas is allowed to expand from 1 m 3 to 3 m 3. The heat added to the system during the expansion was 200 kJ and the change in energy of the system is 340 kJ. Find the gas pressure, in kPa. Known: A gas expands inside a vertical piston-cylinder; E=340 kJ; Q = 200kJ Find: P, [kPa] Sketch: Assumptions: Closed System, Isobaric Solution:

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Matter and Energy Energy can go into or out of a system as either work or heat …so far we’ve covered: Thermodynamics - “the study of systems and energy transfer” Work: Mechanical Work = F x d Exp./Compr. Work Energy, (E): Potential Energy (PE) = m g h Kinetic Energy (KE) = Internal Energy (U) Heat: Heat (Q) } E = PE + KE + U

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