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Railways NTPC (Technical Ability) Thermodynamics Question Bank Thermodynamics

  • question_answer
    An electric motor of 5 kW is subjected to a braking test for 1 hour. The heat generated by the frictional forces in the process is transferred to the surroundings \[20{}^\circ C.\] The resulting entropy change will be:

    A) 22.1 kJ/K                      

    B) 30.2 kJ/K

    C) 61.4 kJ/K                      

    D) 82.1 kJ/K

    Correct Answer: C

    Solution :

    \[h=T.ds\] \[5\times 3600=(273+20).ds\] \[ds=\frac{5\times 3600}{293}=61.4\,\,\text{kJ/K}\]


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