Posted by Z32 on Tuesday, October 6, 2009 at 8:08pm.
[Exponential growth & decay]
The halflife of radioactive strontium90 is approximately 29 years. In 1965, radioactive strontium90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only 14 percent of the original amount absorbed remains?
time= ____ years

Calculus  Reiny, Tuesday, October 6, 2009 at 8:25pm
Many mathteachers use base e for most exponential problems of this type, but since "halflife" is involved, let's use 1/2 as the base
amount = a(1/2)^(t/k) or
amount = a(2)^(t/k) where a is the initial amount, t is the time in years, and k will be 29
so we have to solve
.14 = 1(2)^(t/29(
take the ln of both sides
ln .14 = t/29(ln 2), hope you know your log rules
t/29 = ln .14/ln 2
t/29 = 2.8365
t = 82.26 years.
check: after 29 years, we have 50% left
after 58 years we have 25% left
after 87 years we would have 12.5% left.
our answer appears reasonable.
Answer This Question
Related Questions
 Calculus  The halflife of radioactive strontium90 is approximately 31 years. ...
 Calculus  The halflife of radioactive strontium90 is approximately 31 years. ...
 Math  The halflife of radioactive strontium90 is approximately 32 years. In ...
 Math  The halflife of radioactive strontium90 is approximately 28 years. In ...
 Calculas  In the early 1960s, radioactive strontium90 was released during ...
 calculus  In the early 1960s, radioactive strontium90 was released during ...
 Forensics  Strontium90 is a radioactive waste product from nuclear reactors. ...
 AP Environmental Science (URGENT)  Strontium90 is a radioactive waste product ...
 chem  Radioactive substances decay by firstorder kinetics. How many years ...
 Science  Can anyone help me find the halflife of strontium90? I also need an ...
More Related Questions