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RAJASTHAN ­ PET Rajasthan PET Solved Paper-2011

  • question_answer
    A body cools in 7 min from\[60{}^\circ C\]to\[40{}^\circ C\]. What time does it take to cool from\[40{}^\circ C\]to\[28{}^\circ C\]if the surrounding temperature is\[10{}^\circ C\]?

    A)  3.5 min        

    B)  14 min

    C)  7 min          

    D)  10 min

    Correct Answer: C

    Solution :

     Rate of cooling \[\frac{dQ}{dt}\propto \]temperature difference Ist case \[\frac{60-40}{7}=k(60-10)\] \[k=\frac{2}{35}\] IInd case \[\frac{40-28}{t}=k(40-10)\] \[t=7\text{ }\min \]


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