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

  • question_answer
    A body cools from \[{{50.0}^{o}}C\] to \[{{49.9}^{o}}C\] in \[5\ s\]. How long will it take to cool from \[{{40.0}^{o}}C\] to \[{{39.9}^{o}}C\]? Assume the temperature of surroundings to be \[{{30.0}^{o}}C\] and Newton's law of cooling to be valid                                                      [CBSE PMT 1994]

    A)            2.5 s                                         

    B)            10 s

    C)            20 s                                          

    D)            5 s

    Correct Answer: B

    Solution :

                       \[\frac{50-49.9}{5}=K\,\left( \frac{50+49.9}{2}-30 \right)\]         ?..(i)                    \[\frac{40-39.9}{t}=K\,\left[ \frac{40+39.9}{2}-30 \right]\]          ?..(ii)            from equations (i) and (ii) we get t » 10 sec.


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