00:01
In this problem you have a square and in each corner you have a charge.
00:06
We are given the actual charges, magnitude and sine, and the size of the side of the square.
00:12
That's in centimeters.
00:13
Don't forget to convert that to meters.
00:15
We'll do that later.
00:17
Now let's mark on the diagram the sines because that's all that matters.
00:22
If you have the same sine, repulsion.
00:25
Opposite sines, traction.
00:26
So that's what we need to draw our force diagram.
00:30
Force factors.
00:32
So plus is minus.
00:33
The one is a plus.
00:35
Two is minus.
00:37
Three is a plus.
00:39
Four is a minus.
00:41
So now we can look at the goals to find the x component of the net on three and the y component of the net on three.
00:49
So we're going to start looking at the forces that one, two and four put on three.
00:56
Okay let's look at one on three.
00:58
Plus, plus, repulsion.
01:01
Don't read anything into the length of my arrows just to be representative of the direction.
01:09
Two, three, minus, plus, opposite.
01:12
So attraction.
01:19
Four, three, minus, plus, traction.
01:29
Okay now let me fix this.
01:33
It's a little long.
01:35
You want it long.
01:37
Remember it's always along the connecting line.
01:42
So that's a little better.
01:44
This is a square.
01:45
So this angle diagonal makes is 45 degrees.
01:50
This we're going to need.
01:51
We always need the length between the charges.
01:54
But one and three and four and three are just a's.
01:56
That's easy.
01:57
Two to three we have the length of the diagonal.
01:59
But that is a squared plus a squared.
02:04
And this is equal to a times the square root of two.
02:11
Okay so now we can start looking at the components.
02:17
Now remember though the formula for coulomb's law.
02:20
It's electrostatic constant.
02:22
Magnitude of the first charge.
02:24
Magnitude of the second charge over the distance between them.
02:28
That's the magnitude.
02:30
So let's look at f net x.
02:35
F one three has no x component.
02:38
So zero plus f two three cosine 45 degrees plus f four three.
02:47
Because there's no angle involved.
02:48
It's only in positive x.
02:51
And now we can use coulomb's law and write this out...