Physics

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A first order exponential decay can be written as
A(t)= Ae^(-t/r)
where A(t) is the amount (of substance) after time t, A is the initial amount at time t=0 and r is the decay time.

The fall time is defined as the time in which A(t) falls from 90% to 10% of its initial value. Find the relationship between the fall time of an exponential decay and r.

• Physics -

I will start it off

.9=e^t1/r
ln .9 = t1/r
likewise..
ln .1=t2/r

tfall=t2-t1, well you do that...

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