00:01
Section 6 .4, problem number 29, they introduced the concept of a mean life of a radioactive nuclei.
00:10
So we're dealing with radioactive decay.
00:12
So we've got a formula, exponential decay, y is equal to y -siv0, e to minus kt.
00:18
They introduced a concept that's called the mean life.
00:22
And the mean life tells us that the amount of decay that will have at a certain rate.
00:33
But they're asking us to say in three of these mean lifetimes, we will have decayed about 95 % of the original sample.
00:43
Okay.
00:44
So if the mean life is 1 over k, then three mean lifetimes is just 3 times 1 over k or 3 over k.
01:02
So we're going to go to our formula.
01:04
Y is equal to y sub 0 e to the minus k t and we're going to let t equal three over k we're going to go through three mean lifetimes so what this will give us is that y is equal to y sub zero e to the minus k times three over k so y is equal to y sub zero e to the minus three so at the end of three mean lifetimes, this is the amount that i have less.
01:45
So i start out with, so i start with y is equal to y sub zero, e to the minus kt, and then i end with y is equal to y sub zero, e to the minus three...