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Physics - Entropy, 2nd law of thermodynamics

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  • WoAiMeiMei
    WoAiMeiMei's Avatar
    180 posts since Jul '07
    • 17 Apr `08, 8:35PM

      ahh im having problems with these 2 remaining questions

      SOLVED : P8 (mistake with scale)
                         P28

       


      Notes:



      P32 (Part b) - how do i do this? hint is given below
      How are pressure and volume are related in an adiabatic expansion? Can you determine the type of gas from the value of gamma γ? How much heat is involved in an adiabatic process? In which process, A to B or C to D, is heat absorbed? Lost? Can you get the temperature change in terms of the product of pressure and volume? How is efficiency related to the heat gained and heat lost?

       

       

      *expired notes*

       

      P8 - The line is not linear.
      i tried formula delta s = cm ln (Tf / Ti)
      which is 125 = c x 0.376 x ln (390 / 300)
      Correction: it should be 125 = c x 0.376 x ln (390 / 315)

       


      P28 - W=Qh-QL, Qh/Th=QL/TL and P=W/t.... what do i do? t=1? i did it and it gives me 388 W again. would both answers a and b be the same?

      Edited by WoAiMeiMei 20 Apr `08, 7:51PM
  • WoAiMeiMei
    WoAiMeiMei's Avatar
    180 posts since Jul '07
  • justinfoo
    justinfoo's Avatar
    18 posts since Oct '02
    • 20 Apr `08, 12:54AM

      If I'm not wrong,

      P28

      You need to find the entropy, S

      Let Sb = entropy of saturated water at 132 + 273 = 405K and Sa = entropy of saturated steam at 405K

      Look for values of both entropy from steam tables....

      Then use : Qh = Th(Sb - Sa)    and Qc = Tc(Sb - Sa)

  • WoAiMeiMei
    WoAiMeiMei's Avatar
    180 posts since Jul '07
    • 20 Apr `08, 7:48PM

      28 part a:

       

      i used e= w/q(h) to give q(h)....

       

      so the answer is like 2219.49 W

       

      trying to do part b

  • WoAiMeiMei
    WoAiMeiMei's Avatar
    180 posts since Jul '07
    • 20 Apr `08, 7:50PM

      woot! part b = 1831.4915 W

       

      i just did...

       

      405 - 334.2 = 1.2118

      1 - ans = efficiency

       

      388 / efficiency = 1831W

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    eagle
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