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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 minute to cool from 80°C to 50°C. How much time it will take to cool from 60°C to 30°C, if room temperature is 20°C.                                                     [RPET 1998]

    A)            40 minute                              

    B)            9 minute

    C)            30 minute                              

    D)            20 minute

    Correct Answer: B

    Solution :

                       According to Newton?s law of cooling                     in first case,\[\frac{80-50}{5}=K\left[ \frac{80+50}{2}-20 \right]\]           ?..(i)                    in second case,\[\frac{60-30}{t}=k\left[ \frac{60+30}{2}-20 \right]\]      (ii)            Dividing equation (i) by (ii) we get, \[\frac{t}{2}=\frac{45}{25}\]Þ\[t=9\]min.


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