00:02
All right.
00:03
So you have a handful of homework problems that you wanted to help on.
00:06
I'm going to give you an example of each of them and then give you some time to or give you a chance to practice the other ones.
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I don't want to do the entire homework assignment for you.
00:18
And then you aren't able to do the questions without help.
00:25
So we want you to get to the point where you're independent.
00:28
So there are three equations for this homework assignment.
00:31
The first.
00:32
One is the gravity equation that i have written here on the first on the top left.
00:39
So the law of gravitation by isaac newton, he discovered that if i take a capital g, which is the gravity constant times the mass of the first object, times the mass of the second object, divided by how far apart they are squared, i can get how much force of gravity there is in newton's.
01:02
And so i'll show you an example of that.
01:04
If i use the example of the question where it's the sun and another planet, and i want to know what the force of gravity is between them, that's one of the questions that you have in your homework.
01:17
I can set that up by saying fg is equal to capital g, which is always 6 .67 times 10 to the negative 11th times the mass of the planet, which your homework problem gives is 3 times 10 to the 24th, times the mass of the sun, which is 2 times 10 to the 30th, all of this divided by how far apart the planet and the sun are, which was also given in your problem as 4 .8 times 10 to the 11th.
01:54
And i'm going to square that.
01:57
So if i put all of this into the calculator, i get a force of gravity of 1 .3 .3.
02:04
Times 10 to the 21st newton's.
02:09
And it's two significant figures like they had asked for in your problem.
02:14
It's an extremely large number, but again, we're dealing with planet -sized objects in the sun.
02:20
So it should be a very large number.
02:23
The force of gravity between these two is 1 .7 times 10 to the 21st newton's.
02:29
So that's a good example of how to use the force of gravity equation.
02:33
The main thing to remember is m1 and m2 are the two objects that you're comparing and how far apart they are is the r value.
02:43
And the capital g is always that same number, 6 .67 times 10 and negative 11th, as long as i'm using kilograms and meters in my measurements.
02:55
The second equation here is the density equation.
03:02
And that's mass divided by volume.
03:04
And there's an example of this where in your homework problem, they're talking about an object that's displacing water.
03:14
It's an object that has a mass of 44 and it's displacing 6 .3 liters of water.
03:22
Well, we can use that to find the density of the object by saying, well, m is the mass 44 kilograms divided by the volume.
03:35
Which is the water being displaced.
03:38
It said that there was 6 .3 liters that were displaced.
03:42
If i do that division, i get 7 .0...