00:01
So in this question, we have a pendulum of length l, where this point here has a position x -tilda of t equals, or sorry, we're calling this psi of t equals a -cos omega -t.
00:27
And then let's say we have this angle here, theta, and this point here has a mass of m.
00:34
Then there's going to be a force here, m g.
00:43
And this is going to cause a restoring force.
00:48
This is the restoring force here, minus m g sine theta.
00:57
Now the position here, x, x is going to be l sine theta plus sigh of t.
01:14
So for small angles theta, we have x is approximately l theta plus xxai of t.
01:26
So l theta plus a cos omega -t.
01:33
Now there's also a drag force, fd, is minus b, dx by dt.
01:43
So that's the x components of that force.
01:47
And we're also, what else are we going to have? so, yeah.
01:56
So now we can say that, well, we've got this restoring force here.
02:06
So f restoring is minus mg sine theta, which is approximately minus mg theta.
02:15
But theta equals x over l minus a over l cos omega t.
02:26
So this restoring force here is minus mg times this stuff.
02:34
So we've got the restoring force in terms of x is going to be minus mg theta of x.
02:43
So minus m g over l x plus mg a over l cos omega t.
02:52
So now we've got these two restoring, well we've got these two forces which are acting on the object.
02:58
So we can write newton's second law, m, d2x by dt squared, is the sum of these two forces.
03:07
So minus b, the x by dt.
03:11
Now we're going to use g over l is omega -naught squared, because we're told that in the question.
03:15
So minus m omega -naut squared x plus m -a, omega -naut -squared, cos omega -t.
03:22
So now this is the equation m d2x by d t squared plus b d x by d t plus m omega nought squared x is equal to m omega nought squared a cos omega t.
03:44
Now let's say that x is the real part of a complex variable z equals x plus i y...