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JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2013

  • question_answer
        A body cools from\[50{}^\circ C\]to\[49.9{}^\circ C\]in 5 s. How long will it take to cool from\[40{}^\circ C\]to\[39.9{}^\circ C\]? [Assume   the   temperature   of the surroundings to be\[30{}^\circ C\]and Newtons law of cooling to be valid]

    A)  2.5s                      

    B)  5s  

    C)  20s                       

    D)  10s

    Correct Answer: D

    Solution :

                    From Newtons law of cooling \[E=\left( \frac{{{\theta }_{1}}+{{\theta }_{2}}}{2}-\theta  \right)t\] \[\left( \frac{50+49.9}{2}-30 \right)5=\left( \frac{40+39.9}{2}-30 \right)t\]                 \[t=\frac{19.95\times 5}{9.95}\]                 \[=\frac{99.75}{9.95}\approx 10\,s\]


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