Question 946030: Radium-221 has a half-life of 30 sec. How long will it take for 91% of a sample to decay? (Round your answer to the nearest whole number.)
You can put this solution on YOUR website! Radium-221 has a half-life of 30 sec. How long will it take for 91% of a sample to decay?
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That leaves 9% remaining
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The formula; A = Ao*2^(-t/h) where:
A = remaining amt after t time
Ao = initial amt (t=0)
t = time of decay
h = half-life of substance
In this problem let Ao = 1, then A = .09, given half-life of 30 sec
1*2^(-t/30) = .09
log(2^(-t/30) = log(.09)
log equiv of exponents *log(2) = log(.09) =
use the calc to find the logs = -3.474
multiply both sides by -30
t = -30 * -3.474
t = +104.2 ~ 104 seconds
You can put this solution on YOUR website! Material has half life of t seconds. How long will it take for s percent of Material sample to decay?
Question is to find how much time until quantity present changes from I to .
First find k, and then use k to find time to let s percent of sample to decay.
, you know t=30 seconds and want the value... .
Model Revised: .
Starting with I=1, t is what when ?
(Your value given for s is 91).
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t=-ln(1-s/100)/(-0.0231)
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Easier to avoid sign mistakes if directly using the actual values. , seconds.
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