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JEE Main & Advanced Physics Transmission of Heat Question Bank Radiation Newton's Law of Cooling

  • question_answer
    A body takes 5 minutes to cool from 90oC to 60oC. If the temperature of the surroundings is 20oC, the time taken by it to cool from 60oC to 30oC will be.     [RPMT 2003]

    A)            5 min                                       

    B)            8 min

    C)            11 min                                     

    D)            12 min

    Correct Answer: C

    Solution :

                       \[\frac{90-60}{5}=k\left( \frac{90+60}{2}-20 \right)\]Þ \[6=k\times 55\] Þ \[K=\frac{6}{55}\]            And, \[\frac{60-30}{t}=\frac{6}{55}\left( \frac{60+30}{2}-20 \right)\]Þ t = 11 minute.


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