00:01
So we have the pendulum swinging, and we know that the first swing of that pendulum is two feet.
00:06
And then each successive one, our constant ratio is 0 .9.
00:10
So on part a, we want to find how far will it have traveled on its, how far will it travel on its tenth swing? and so we know that our rule will end up being for a particular swing, the n swing, is 2 times 0 .9 to the n -1.
00:29
So this one will be 2 times 0 .9 to the 10 minus 1 will be to the 9th hour.
00:35
And when we type that in, we get 0 .775 feet.
00:41
Now part b asks us what will be the first time where that swing is less than this value? and we could do it with trial and error.
00:50
Or you could take the point dysfunction and try to find when it equals 1.
00:55
Dividing both sides by 2, i'd have 0 .9 to the n minus 1 is equal to 0 .5.
01:01
And again, tuck the log of both sides.
01:03
Doesn't matter whether you do it in natural log or common log...