Results 1 to 2 of 2

Math Help - radioactive

  1. #1
    Newbie
    Joined
    Oct 2007
    Posts
    2

    radioactive

    The level of radioactivity on the site of a nuclear explosion is decaying exponentially. The level measured in 1970 was found to be 0.7 times the level measured in 1960. What is the half-life. (the amount of years)
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Bar0n janvdl's Avatar
    Joined
    Apr 2007
    From
    Meh
    Posts
    1,630
    Thanks
    6
    Radioactivity in 1970 = x

    Radioactivity in 1960 = y

    But x = 0,7y

    0,7y = y(1 - \frac{r}{100} ) ^{10}

    0,7 = (1 - \frac{r}{100} ) ^{10} [Divide by y]

    (1 - \frac{r}{100} ) = \sqrt[10]{0,7}

    (1 - \frac{r}{100} ) = 0,9649

    \frac{r}{100} = 0,0350

    r = 3,503

    I think this is the rate at which it is decaying. I'll spend a little more time on it...



    EDIT: Okay i got it! We now have the rate, so we want to know when x = 0,5y

     0,5y = y(1 - \frac{3,503}{100}) ^ {n}

     0,5 = (1 - \frac{3,503}{100}) ^ {n}

     n = log_{ 1 - \frac{3,503}{100} }{0,5}

     n = 19,43 \ years
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Radioactive decay
    Posted in the Differential Equations Forum
    Replies: 1
    Last Post: February 22nd 2011, 12:45 AM
  2. radioactive
    Posted in the Calculus Forum
    Replies: 3
    Last Post: August 9th 2010, 02:39 PM
  3. Radioactive Decay
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: February 11th 2009, 06:31 PM
  4. radioactive
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: October 29th 2007, 01:14 PM
  5. Radioactive
    Posted in the Pre-Calculus Forum
    Replies: 5
    Last Post: July 11th 2006, 09:02 AM

Search Tags


/mathhelpforum @mathhelpforum