Uttarakhand PMT Uttarakhand PMT Solved Paper-2004

  • question_answer
    The mass of an object changes from 0.2 g to 0.025 g in 1500 years. The half life of the object is:

    A)  500 yrs      

    B)  600 yrs

    C)  800 yrs      

    D)  950 yrs

    Correct Answer: A

    Solution :

     Given that Initial value No = 0.2 gm. Final value (N) = 0.025 gm Time decay (T) = 1500 yrs. By using: \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{n}}\] \[\frac{0.025}{0.2}={{\left( \frac{1}{2} \right)}^{n}}\] Or \[\frac{1}{8}={{\left( \frac{1}{2} \right)}^{n}}\] Or \[{{\left( \frac{1}{2} \right)}^{3}}={{\left( \frac{1}{2} \right)}^{n}}\] Or \[n=3\] Now by using \[{{t}_{1/2}}=\frac{T}{n}=\frac{1500}{3}\] \[=500\text{ }yrs\]


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