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Railways NTPC (Technical Ability) Thermodynamics Question Bank Thermodynamics

  • question_answer
        A system undergoes a change of state during which 80 kJ of heat is transferred to it and it does 60 kJ of work. The system is brought hack to its original slate through a process during which 100 kJ of heat is transferred to it. The work done by the system is:

    A) 40 kJ                

    B) 60 KJ           

    C) 120 kJ              

    D) 180 kJ   

    Correct Answer: C

    Solution :

    \[{{Q}_{1\,-\,2}}=+\,80\,\,kJ,\] \[{{W}_{1\,-\,2}}=+\,\,60\,\,kJ,\] \[{{Q}_{1\,-\,2}}={{W}_{1\,-\,2}}+{{U}_{12}}\] \[{{U}_{12}}=80-60=20\,\,kJ\] \[{{Q}_{2\,-\,1}}={{W}_{2\,-\,1}}+{{U}_{21}}\] \[100={{W}_{2\,-\,1}}-20\] \[{{W}_{2\,-\,1}}=100+20=120\,\,kJ\]


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