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Railways NTPC (Technical Ability) Thermodynamics Question Bank Thermodynamics

  • question_answer
    A system undergoes a change of state during which 100 kJ of heat is transferred to it and it does 50 kJ of work. The system is brought back to its original state through a process during which 120 kJ of heat is transferred to it. What is the work done by the system?

    A) 50 kJ                

    B) 70 kJ

    C) 120 kJ              

    D) 170 kJ

    Correct Answer: D

    Solution :

    \[{{Q}_{1\,-\,2}}=+\,100\,\,kJ,\] \[{{W}_{1\,-\,2}}=+\,50\,\,kJ\] \[{{Q}_{1\,-\,2}}={{W}_{1\,-\,2}}+{{U}_{1\,-\,2}}\] \[{{U}_{1\,-\,2}}=100-50=50\,\,kJ\] \[{{Q}_{2\,-\,1}}={{W}_{2\,-\,1}}+{{U}_{2\,-\,1}}\] \[120={{W}_{2\,-\,1}}-50\] \[{{W}_{2\,-\,1}}=170\,\,kJ\]


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