SOLUTION: Can you please help me answer with the answer to problem for my son; then I can walk him through it. It is quite lengthy and involved. Carbon-14 is an isotope of carbon that is fo

Algebra ->  Exponential-and-logarithmic-functions -> SOLUTION: Can you please help me answer with the answer to problem for my son; then I can walk him through it. It is quite lengthy and involved. Carbon-14 is an isotope of carbon that is fo      Log On


   



Question 135981: Can you please help me answer with the answer to problem for my son; then I can walk him through it. It is quite lengthy and involved.
Carbon-14 is an isotope of carbon that is formed when radiation from the sun strikes ordinary carbon dioxide in the atmosphere. Trees, which get their carbon dioxide from the air, contain small amounts of carbon-14. Once a tree is cut down, no more carbon-14 is formed, and the amount that is present begins to decay slowly. The half-life of the carbon-14 isotope is 5730 yr.
A)Find an equation that models the percentage of carbon-14 in
a sample of wood. (Consider that at time zero there is 100%
and that at time 5730 yr there is 50%.)
B)A piece of wood contains 48.37% of its original carbon-14. According to this information, approximately how long ago did the tree that it came from die? What assumptions are you making, and why is this answer approximate?
I'm sorry but I don't have the ISBN number; I only copied the page I needed from the book.

Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
1. A half life equation has the form of
N%28t%29+=+N%5B0%5De%5E%28-%28alpha%29t%29
and you calculate N%5B0%5D and alpha using the clues provided.
At time t=0, the value of N(0)=100.
N%280%29=N%5B0%5De%5E%280%29=100
N%5B0%5D=100
since e%5E%280%29=1.
Also, at t=5730, N(t)=50.
50=100e%5E%28-%28alpha%295730%29
0.5=e%5E%28-%28alpha%295730%29
ln%280.5%29=-%28alpha%295730%29
-0.693147=-%28alpha%295730%29
%28alpha%29=0.693147%2F5730%29
%28alpha%29=0.00012097%29
N%28t%29+=+100e%5E%28-%28.00012097%29t%29
2. Now that you have the equation, calculations are easy.
N%28t%29+=+100e%5E%28-%28.00012097%29t%29
48.37+=+100e%5E%28-%28.00012097%29t%29
.4837+=+e%5E%28-%28.00012097%29t%29
ln%28.4837%29+=+-%28.00012097%29t%29
.7262904=.00012097t
t=6003.888