00:01
So this problem involves kulam's law as well as some geometry.
00:09
Let's first write down kulam's law, so remember what it is.
00:12
It says the electrical force between two charges is equal to a constant, known as kulam's constant, times the magnitude of one of the charges, times the magnitude of the other charge, divided by the distance between the two charges squared.
00:33
Now, in this particular case, the charges are all negative, which means they're gonna be repulsive.
00:46
The way to figure out the direction of this force is to say that if the charges are like charges, the force is gonna be repulsive, the charges are unlike charges, the force is gonna be attractive.
00:58
But because the forces are all repulsive, the net force on the top charge, see i've got this little triangle drawn here.
01:08
On the top charge, there's going to be a force from the one in the bottom left going up this way.
01:13
And there's going to be a force from the bottom right going up this way.
01:18
And those two by symmetry will be equal in magnitude, but they'll point in different directions.
01:24
And we can get the directions here from using a little geometry.
01:33
We know that this angle, here is 60 degrees because this is an equilateral triangle and so we can also conclude that the angle here must similarly be 60 degrees which means that we know and by symmetry we know then that this y axis here on this free body diagram must bisect an angle so each of these angles here is 30 degrees so it using that information and using the, we'll calculate the forces up here using that format and then we'll figure out what the net force is caused by those two forces on this third object here.
02:25
Well clearly the horizontal components of each of these forces, you know this one will go off this way in this direction and this horizontal component from the one on the right will go off this way and by symmetry they're the same size but they're going on out to direction.
02:42
So those two will simply add up to zero.
02:45
They can't stutter out.
02:47
But the vertical components, that is to say, this component of this one, and this component of this one, like i made those two horizontal component too big, but that's okay.
02:58
These two vertical components will add up...