SOLUTION: 5. The level of thorium in a sample decreases by a factor of one-half every 2 million years. A meteorite is discovered to have only 8.6% of its original thorium remaining. How ol

Question 199966: 5. The level of thorium in a sample decreases by a factor of one-half every 2 million years. A meteorite is discovered to have only 8.6% of its original thorium remaining. How old is the meteorite?
I dont get these problems can anyone help?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
The level of thorium in a sample decreases by a factor of one-half every 2 million years.
A meteorite is discovered to have only 8.6% of its original thorium remaining.
How old is the meteorite?
:
The half life equation
Ao*(2^(-t/h)) = A
Where
A = resulting amt
Ao - initial amt
t = time
h = half-life of the substance
:
Time in this problems is millions of yrs:
Let Ao = 100
then
A = 8.6
h = 2 (million yrs)
Find t in millions of yrs
:
100(2^(-t/2)) = 8.6
2^(-t/2) =
2^(-t/2) = .086
:
log(2^(-t/2)) = log(.086)
;
log equiv of exponents
log(2) = log(.086)
:
find the logs
= -1.0655
Multiply equation by 2
-.301t = 2(-1.0655)
:
-.301t = -2.131
t =
t = 7.078 million years
:
:
Check solution on calc: enter: 2^(-7.078/2)*100 = 8.6%

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