college physics part 2

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the activity of a sample of carbon has one-eighth of the initial activity. carbon-14 has a half-life of 5730 yr. how old is the sample in yr?

  • college physics part 2 -

    one eighth is three half-lives.

    Now the hard way:

    amount left=original amount(1/2)^t/thalflife

    1/8=(1/2)^t/th

    t/th=3

    or even harder:

    amountleft=original*e^-.693t/th

    1/8=e^-.693 t/th

    ln of each side

    ln (1/8)=-.693 t/th
    -2.0793=-.693 t/th

    t/th= 3

  • college physics part 2 -

    the question ask how old is the sample in yr. so that mean t/th is 3 yrs.

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