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J & K CET Engineering J and K - CET Engineering Solved Paper-2014

  • question_answer
    The half life of an old rock element is 5800 years. In how many years its sample of \[25\text{ }g\]is reduced to \[6.25\text{ }g\].

    A)  \[2900\text{ }years\]       

    B)  \[5800\text{ }years\]

    C)  \[11600\text{ }years\]       

    D)  \[23200\text{ }years\]

    Correct Answer: C

    Solution :

    \[25g\xrightarrow{{{T}_{1/2}}}12.5g\xrightarrow{{{T}_{1/2}}}6.25g.\] After two half lives the sample will reduce at\[6.25\text{ }g\]. \[\Rightarrow \] So time taken \[t=\frac{2\pi }{2}\] \[=2\times 5800=11600%\]


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