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    millar2009S's Avatar
    millar2009S Posts: 4, Reputation: 1
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    #1

    May 20, 2009, 09:16 AM
    Logarithmic Word equation
    The Amount At, micrograms of a certain radioactiv substance remaining after t years decreases according to the formula At=Aoe^-0.002t , where Ao is the amount present initially

    a) If 600 micrograms are left after 1000years, how many micrograms were present initially?

    b) The half-life of a substance is the time taken for the amount to decrease to half of its initial amount. What is the half-life of this substance?


    :confused:
    galactus's Avatar
    galactus Posts: 2,271, Reputation: 282
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    #2

    May 20, 2009, 09:56 AM
    Quote Originally Posted by millar2009S View Post
    The Amount At, micrograms of a certain radioactiv substance remaining after t years decreases according to the formula At=Aoe^-0.002t , where Ao is the amount present initially
    a) If 600 micrograms are left after 1000years, how many micrograms were present initially?
    Set the equation equal to 600 and t=1000, then solve for

    b) The half-life of a substance is the time taken for the amount to decrease to half of its initial amount. What is the half-life of this substance?
    You are given k=-.002. Half-life is given by the formula

    Just plug in k.
    Libran's Avatar
    Libran Posts: 43, Reputation: 0
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    #3

    May 20, 2009, 09:58 AM

    HaHa.. I remember doing these questions in earlier classes.

    Nyways,
    a) 600 = Ao*e^(-0.002*1000) Find A0
    b) In 2nd part, you are given,A=A0/2, therefore A/a0 =1/2
    Use in eqn. given and find t

    Good luck dear. Best of luck with your exams
    Libran's Avatar
    Libran Posts: 43, Reputation: 0
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    #4

    May 20, 2009, 10:00 AM
    @galactus
    Your signature line "Your Mom is so dumb that she tried to minimize a 12 variable function to a minimal sum of products expression using a Karnaugh Map instead of the Quine-McCluskey algorithm.)" made me die laughing.
    HAHHAHA

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