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AP PHYSICS

AP PHYSICS. Friday, 1/22/09 AP PHYSICS. ret HW 46. p. 423 #59

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AP PHYSICS

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  1. AP PHYSICS

  2. Friday, 1/22/09 AP PHYSICS ret HW 46 p. 423 #59 A 1500W heat engine operates at 25% efficiency. The heat energy expelled at the low temperature is absorbed by a stream of water that enters the cooling coils at 20°C. If 60L flow across the coils per second, determine the increase in temperature of the water.

  3. Reversible process – both system and surroundings can be returned to their exact initial conditions. (An impossible ideal [entropy]) All natural processes are irreversible. A very close real process: slowly dropping sand on the top of an insulated piston that is on a heat reservoir

  4. Carnot Engine – engine operating through an ideal, reversible cycle consisting of 2 adiabatic and 2 isothermal processes (called the Carnot Cycle)

  5. The Carnot Cycle

  6. The Carnot Cycle Effc = (Th – Tc) Th Tc Th = 1 – What is so important about a Carnot Engine?? The Carnot Engine is the most efficient engine possible between 2 given heat reservoir!

  7. Temperature must be in Kelvin!! ex. The exhaust temperature of a Carnot heat engine is 300ºC. What is the intake temperature if the efficiency of the engine is 30%? p. 422 #44 A heat engine operates in a Carnot cycle between 80.0ºC and 350ºC. It absorbs 21,000J of heat per cycle from the hot reservoir. The duration of each cycle is 1.00s. (a) What is the maximum power output of this engine? (b) How much heat does it expel in each cycle? HW 47: ws. Ch. 12/ 22, 23, 25, 29 and 2 AP questions

  8. 22) 48.9% 23) a) 560J b) 350J 25) 19.8% 29) 33.3% 22) 48.9% 23) a) 560J b) 350J 25) 19.8% 29) 33.3% HW 47 HW 47 HW 47 HW 47 22) 48.9% 23) a) 560J b) 350J 25) 19.8% 29) 33.3% 22) 48.9% 23) a) 560J b) 350J 25) 19.8% 29) 33.3%

  9. 1) A heat engine operating between temperatures of 500 K and 300 K is used to lift a 10‑kilogram mass vertically at a constant speed of 4 meters per second. a. Determine the power that the engine must supply to lift the mass. b. Determine the maximum possible efficiency at which the engine can operate. c. If the engine were to operate at the maximum possible efficiency, determine the following. i. The rate at which the hot reservoir supplies heat to the engine ii. The rate at which heat is exhausted to the cold reservoir

  10. 2) A proposed ocean power plant will utilize the temperature difference between surface seawater and seawater at a depth of 100 meters. Assume the surface temperature is 25° Celsius and the temperature at the 100‑meter depth is 3° Celsius. a. What is the ideal (Carnot) efficiency of the plant? b. If the plant generates useful energy at the rate of 100 megawatts while operating with the efficiency found in part (a), at what rate is heat given off to the surroundings? c. A nuclear power plant operates with an overall efficiency of 40 percent. At what rate must mass be converted into energy to give the same 100‑megawatt output as the ocean power plant above? Express your answer in kilograms per second. The diagram below represents the Carnot cycle for a simple reversible (Carnot) engine in which a fixed amount of gas, originally at pressure po and volume Vo follows the path ABCDA. d. In the chart below, for each part of the cycle indicate with +, ‑, or 0 whether the heat transferred Q and temperature change T are positive, negative, or zero, respectively. ( Q is positive when heat is added to the gas, and T is positive when the temperature of the gas increases.)

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