Results 1 to 3 of 3

Math Help - Half-Life Question

  1. #1
    Junior Member
    Joined
    May 2009
    From
    Barrie, Ontario
    Posts
    35

    Half-Life Question

    The half life of carbon-14 is about 5760. If a bone sample only has 15% carbon-14 remaining, determine the age of the bone.

    This question throws me off cause of the percent, if it was in mg's I could do it no problem.

    The only part of the equation that I know is (1/2)^(x/5760) and I don't know where to put the .15 in cause it's not a measurable amount (ie. in mg's).

    All I got is y=a(1/2)^(x/5760)

    If anyone can show me what to do with the 15% it would greatly be appreciated. (I assume I need to find y and a, so I can solve for x)

    Would it be something like .15=1(1/2)^(x/5760)?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    -1
    e^(i*pi)'s Avatar
    Joined
    Feb 2009
    From
    West Midlands, England
    Posts
    3,053
    Thanks
    1
    Quote Originally Posted by peekay View Post

    Would it be something like .15=1(1/2)^(x/5760)?
    Yes, that looks about right, I'll double check and then edit

    Half life: \lambda = \frac{ln(2)}{t_{1/2}} = \frac{ln(2)}{5760}

    Exponential Decay A = A_0e^{-\lambda t} \rightarrow 0.15 = e^{-\frac{ln(2)}{5760}t}

    I'm not sure if they are equivalent functions though - my method yields an answer of 15800 years (3sf)
    Last edited by e^(i*pi); June 20th 2009 at 02:14 PM. Reason: added in minus sign
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    May 2009
    From
    Barrie, Ontario
    Posts
    35
    yeah, i just did it with logs and the answer looks about the same.

    did:

    x/5760=log(.15)/log(.5)
    x/5760=2.736
    x=15764.92

    Thanks for the confirmation!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Half Life Question
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: January 23rd 2010, 07:40 PM
  2. logarithmic half life question
    Posted in the Algebra Forum
    Replies: 2
    Last Post: October 25th 2009, 02:33 PM
  3. Half - Life Question!
    Posted in the Calculus Forum
    Replies: 2
    Last Post: October 2nd 2009, 10:28 PM
  4. Half life question
    Posted in the Pre-Calculus Forum
    Replies: 6
    Last Post: June 17th 2009, 10:20 PM
  5. Half Life Question
    Posted in the Calculus Forum
    Replies: 2
    Last Post: April 1st 2009, 09:59 PM

Search Tags


/mathhelpforum @mathhelpforum