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

  • question_answer
    An object is cooled from 75°C to 65°C in 2 minutes in a room at 30°C. The time taken to cool another object from 55°C to 45°C in the same room in minutes is [EAMCET (Med.) 1996]

    A)            4    

    B)            5

    C)            6    

    D)            7

    Correct Answer: A

    Solution :

                       According to Newton?s law of cooling                    in first case,      \[\frac{75-65}{t}=K\left[ \frac{75+65}{2}-30 \right]\]       ?..(i)                    in second case,\[\frac{55-45}{t}=K\left[ \frac{55+45}{2}-30 \right]\]      ?..(ii)            Dividing eq. (i) by (ii) we get \[\frac{5t}{10}=\frac{40}{20}\]Þ\[t=4\]minutes


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