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PT Unit Five

PT Unit Five. Subunit four. 1 calorie = 4.184 J or 3.086 ft x lb 1 kilocalorie = 4184 J or 3086 ft x lb 1 Btu = 778 ft x lb or 1054 J. A 180 kg reel of wire rotates at 350 rpm (about 37 rad/sec). The effective radius of the reel (sh

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PT Unit Five

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  1. PT Unit Five Subunit four

  2. 1 calorie = 4.184 J or 3.086 ft x lb • 1 kilocalorie = 4184 J or 3086 ft x lb • 1 Btu = 778 ft x lb or 1054 J

  3. A 180 kg reel of wire rotates at 350 rpm (about 37 rad/sec). The effective radius of the reel (sh • aped like a cylinder) 0.41 m. The rotating reel is brought to a stop by a mechanical friction brake with a drum and brake lining. • Find a. Rotational kinetic energy of reel. • B. Heat energy equivalent of rotational kinetic energy.

  4. B. Assume all the kinetic energy goes into heat energy developed during the stopping action of the brake. • Total heat energy developed = • 10.356 J X 1kcal/4184J = 2.475 kcal

  5. Subunit four • Calculate the heat gained by a 15 Kg mass of copper when it is heated from 10°C to 125°C

  6. Subunit four • Calculate the heat gained by a 15 Kg mass of copper when it is heated from 10° • C to 125 °C. • H = mcT • H = 15 kg (.093 kcal/(kg ● °C)) (115 °C) • H = 160.42 kcal

  7. Heat Gained = Heat lost • Heat = mc∆t • Heat = Heat energy transferred • M = Mass • c = specific heat • ∆t = temperature

  8. To harden a steel sledgehammer, a manufacturer heats the 4.5 kg hammer to 650 °C and quenches it in an insulated oil container. The hammer cools to 250 °C. Oil temperature increases from 200 °C to 250 °C. The specific heat of steel is: • c= 0.11 kcal/kg C° • Find amount of heat energy removed from the hammer and added to the oil bath. • Find the specific heat of the oil bath if the mass of the oil is 70 kg.

  9. Three ways to transfer energy • 1. Conduction • 2. Convection • 3. Radiation

  10. Conduction is the transfer of thermal energy from a hot region to a cold region by direct transfer of molecular virbation from molecule to molecule.

  11. Convection is the transfer of thermal energy by movement of a fluid medium from one region to another

  12. Radiation is the transfer of heat energy by motion of electromagnetic radiation. (NO medium required)

  13. Changes of State • Melting = Change from solid to liquid • Freezing = Change from liquid to solid • vaporization = change from liquid to gas • Condensation = change from gas to liquid • Sublimation = change from solid to gas

  14. Sensible heat energy involved when a substance gains energy producing a temperature change. Change in kinetic energy. • Latent heat energy involved when substance undergoes a change of state. • There is no temperature change. Means hidden energy. Change in potential energy.

  15. Latent heat of Fusion: Heat required to melt a gram (kilogram) of a substance. • Latent heat of vaporization: Heat required vaporize a gram (kilogram) of a substance.

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