00:01
So i have a radioactive substance with a decay rate of 3 .6%, so that's going to be negative 0 .036, and i want to know what its half -life is.
00:15
So i'm just going to use an exponential decay model.
00:20
A sub 0 is my initial amount.
00:23
I'm going to have half of that, and i'm solving for t.
00:30
Divide by a sub 0.
00:37
Now take the natural log of both sides.
00:44
Bring down your exponent.
00:48
Ln of e is just 1.
00:53
Then divide by negative 0 .036.
00:59
We want two decimal places, so let's see.
01:02
Ln 0 .5 divided by negative 0 .036.
01:06
That's 19 .2541.
01:10
So that'll be 19 .25 years for that half -life in the first problem.
01:20
Okay, now let's look at the next one.
01:22
This is number 7.
01:25
The half -life of carbon is 5750 years.
01:31
So i'm going to use an exponential decay model again.
01:37
A sub 0 is my initial amount.
01:40
I'm going to have half of that in 5750 years...