Facebook Page
Twitter
RSS
+ Reply to Thread
Results 1 to 1 of 1
  1. MHB Journeyman

    Status
    Offline
    Join Date
    Jan 2012
    Posts
    890
    Thanks
    344 times
    Thanked
    1,039 time
    Thank/Post
    1.167
    #1
    Jimson asks over on

    Quote Quote:
    I've got some A2 physics homework and unfortunately i can't seem to do the first question :
    Quote Quote:

    The question is: 61Co has a half life of 100 minutes. how long will it take for the radioactive isotope to reduce to 80% of the initial value?

    The answer is 32 minutes, but of course i'll need the workings before it to actually prove i can do the question.

    Thank you for any help given! (if any is anyway).

    The key idea is that after 100 minutes 1/2 remains after 200 minutes 1/4 remains so t
    he fraction remaining after \(t\) minutes is:

    \[Q=2^{-t/100}\]

    So if \(80\%\) remains we need to solve:

    \[0.8=2^{-t/100}\]

    which we do by taking logs (the base is unimportant as long as we use the sane base throughout):

    \[\log(0.8)= -\; \frac{t}{100} \log(2)\]

    So:

    \[t=- \; \frac{\log(0.8)}{\log(2)} \times 100\]

  2. # ADS
    Circuit advertisement
    Join Date
    Always
    Posts
    Many
     

Similar Threads

  1. Posterior distribution question Pixie's question from Yahoo Answers
    By CaptainBlack in forum Advanced Probability and Statistics
    Replies: 1
    Last Post: April 28th, 2012, 03:51
  2. [SOLVED] Half annulus 1st and 2nd quadrant
    By dwsmith in forum LaTeX Help and Discussion
    Replies: 4
    Last Post: March 4th, 2012, 21:14

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Math Help Boards