00:01
All right, so this is our first plot, plot a.
00:12
And so here, so this is plot a.
00:16
And what we're doing here is we're just plotting u of r.
00:19
We're scaling u of r by dividing it by u not.
00:23
And that makes it easier to plot against r.
00:28
So first thing to do is find the point at which it crosses the the axis at this point, so this would be u of r equals 0.
00:42
What is r when u is 0? so u .0 times 2 over r squared minus 1 over r be equal to 0.
00:52
So what you have is r squared over 2 equals r.
00:58
So that implies that r is 2.
01:01
So r equals 2.
01:03
Crossing point.
01:05
And the other thing is the minimum, what is the minimum? and so for that, you need to find the derivative, first of all, derivative of u is u0 times negative 4 over r cubed plus 1 over r squared.
01:20
And so you said that equal to zero.
01:23
And what you get is r cubed over 4 equals r squared.
01:27
So r equals 4 is the minimum point.
01:32
And you can see the that agrees with the plot here.
01:37
And then this is part b...