# Universal Gravitation problem, help with final statement.

• Physics345
In summary, a rocket with a mass of 1200 kg is located 3.0x10^8 m from the center of the Earth and directly between the Earth and the moon. The net gravitational force on the rocket from the Earth and moon is 4.5N towards the Earth. This is because the Earth's gravitational pull is about 83% stronger than the moon's pull on the rocket.
Physics345

## Homework Statement

earth has a mass of 5.98x10^24 kg and the moon has a mass of 7.35x10^22 kg. The distance from the centre of the moon to the centre of the Earth is 3.84x10^8 m. A rocket with a total mass of 1200 kg is 3.0x10^8 m from the centre of the Earth and directly in between Earth and the moon. Find the net gravitational force on the rocket from the Earth and moon.

## Homework Equations

Fnet=Gm1m2/r^2 + Fnet=Gm2m3/r^2

## The Attempt at a Solution

Rocket to earth:
Fnet=5.32N=5.3N
Rocket to the moon:
Fnet=5.32N-0.833
Fnet=4.48N=4.5N rounded
Therefore, the net force of the rocket to the moon is 4.5N Right and the net force from the rocket to Earth is 5.3N Left.

I was just wondering if my Final statement is correct.

Physics345 said:
Fnet=Gm1m2/r^2 + Fnet=Gm2m3/r^2
Physics345 said:
the net force of the rocket to the moon
You do not seem to understand "net force". It is the sum of all the applied forces, so there is only one net force on the object.
Physics345 said:
4.5N Right
Left/right depends on your diagram. Better to write in terms of "towards moon" or "towards Earth".

Fnet means the total/sum of all forces. That was a typo I meant to put FgE= Gm1m2/f13 FgM=Gm2m3/f23 Fnet=FgE-FgM fatigue is very intoxicating but thanks I figured out the answer to my question anyways. The answer is 4.5N Right towards the Moon and 4.5 Left towards Earth.

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Physics345 said:
Fnet means the total/sum of all forces. That was a typo I meant to put FgE= Gm1m2/f13 FgM=Gm2m3/f23
Ok, but my comment still applies to your answer. You are asked for the net force; that's just one force, not a separate force towards each attractor.

Sorry I edited my comment, I'm just really tired I edited as you replied, so I can see how you came to that conclusion.

Physics345 said:
4.5N Right towards the Moon and 4.5 Left towards Earth.
Better, but as I wrote, left and right refer to some diagram (that I cannot see). Just write that it is 4.5N towards ... which one?

Physics345 said:
No, I don't need the diagram. The point is that you should not be referencing a diagram in your answer.

haruspex said:
No, I don't need the diagram. The point is that you should not be referencing a diagram in your answer.
Oh, I should be stating 4.5N Towards the Earth and 4.5N Towards the moon. Wow I feel silly, left and right shouldn't even be stated in this scenario.

Statement revised, here is my new final statement. Therefore, the net force of the rocket towards the Moon is 4.5N, and 4.5N towards the Earth.

Physics345 said:
Statement revised, here is my new final statement. Therefore, the net force of the rocket towards the Moon is 4.5N, and 4.5N towards the Earth.
There is a single net force on the rocket. You can specify it as a magnitude and direction. Magnitudes are non-negative by definition. Direction is either towards the moon or towards the Earth. Which?

haruspex said:
There is a single net force on the rocket. You can specify it as a magnitude and direction. Magnitudes are non-negative by definition. Direction is either towards the moon or towards the Earth. Which?
Towards the Earth because the Earths gravitational pull is pulling the rocket!

Physics345 said:
Towards the Earth because the Earths gravitational pull is pulling the rocket!
They are both pulling the rocket. Which wins?

haruspex said:
They are both pulling the rocket. Which wins?
I would have to say the Earth wins, considering that the gravitational pull of the Earth is about 83% greater than the moons even after taking the altitude of the rocket into account.

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Wow it says it in my answer, the pull of the Earth on the rocket is 5.3N as opposed to the moon, which has a measly 0.8338N.

Physics345 said:
Wow it says it in my answer, the pull of the Earth on the rocket is 5.3N as opposed to the moon, which has a measly 0.8338N.
Right!
So why did you write this:
Physics345 said:
4.5N Right towards the Moon and 4.5 Left towards Earth
and this:
Physics345 said:
the net force of the rocket towards the Moon is 4.5N, and 4.5N towards the Earth.
(which would add to zero net force) and this:
Physics345 said:
because the Earths gravitational pull is pulling the rocket!
?

The answer was in my face this whole time I feel very dumb. Considering the lack of sleep I've had lately it's reasonable, well I probably should head to bed and catch up on some needed sleep. I'm sure this was frustrating for you, I can just imagine... I was able to do the math perfectly but I couldn't get the wording out for the final statement. Thanks a lot though I really appreciate it. Note,I wrote all that because I'm honestly being brain dead right now. I can write out all the math flawlessly my issue is wording when it comes to science I over think things and over complicate science a lot. But with more studying and practice I should have all this down to the point you'll see me on here helping people out =). If you want I could type out all the math I wrote but I decided to type out as little as possible because I was tired, but now that I want to prove a point here's the math:
FgE= Gm1m2/F13 FgM=Gm2m3/F23
Fnet=FgE - FgM
F13(distance Earth to rocket)=3.0 x 10^8
F23(distance rocket to earth)=(3.84 x 10^8) - (3.0 x 10^8)= 8.4 x 10^7
Fnet=(6.67 x 10^-11)(5.98 x 10^24)(1.2 x 10^3)/(3.0 x 10^8)^2 - (6.67 x 10^-11)(1.2 x 10^3)(7.35 x 10^22)/(8.4 x 10^7)^2
Fnet=5.32N - 0.8338N
Fnet=4.5N

Last edited:
Physics345 said:
The answer was in my face this whole time I feel very dumb. Considering the lack of sleep I've had lately it's reasonable, well I probably should head to bed and catch up on some needed sleep. I'm sure this was frustrating for you, I can just imagine... I was able to do the math perfectly but I couldn't get the wording out for the final statement. Thanks a lot thought I really appreciate it. Note,I wrote all that because I'm honestly being brain dead right now. I can write out all the math flawlessly my issue is wording when it comes to science I over think things and over complicate science a lot. But with more studying and practice I should have all this down to the point you'll see me on here helping people out =). If you want I could type out all the math I wrote but I decided to type out as little as possible because I was tired, but now that I want to prove a point here's the math:
FgE= Gm1m2/F13 FgM=Gm2m3/F23
Fnet=FgE - FgM
F13(distance Earth to rocket)=3.0 x 10^8
F23(distance rocket to earth)=(3.84 x 10^8) - (3.0 x 10^8)= 8.4 x 10^7
Fnet=(6.67 x 10^-11)(5.98 x 10^24)(1.2 x 10^3)/(3.0 x 10^8)^2 - (6.67 x 10^-11)(1.2 x 10^3)(7.35 x 10^22)/(8.4 x 10^7)^2
Fnet=5.32N - 0.8338N
Fnet=4.5N
OK!
Get some rest...

Physics345
HaHa, thanks again. Good night!

## 1. What is universal gravitation?

Universal gravitation is a fundamental physical law that describes the gravitational force between objects with mass. It states that any two objects in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

## 2. How is the gravitational force calculated?

The gravitational force between two objects can be calculated using the equation F = G * (m1 * m2)/d^2, where F is the force, G is the gravitational constant, m1 and m2 are the masses of the objects, and d is the distance between them.

## 3. What is the significance of the universal gravitation law?

The universal gravitation law is significant because it explains the motion of planets and other celestial bodies in our solar system. It also helps us understand the behavior of objects on Earth, such as the motion of objects falling towards the ground.

## 4. How does the strength of gravity vary with distance?

The strength of gravity decreases as the distance between two objects increases. This is because the force of gravity is inversely proportional to the square of the distance between the objects. As the distance increases, the force of gravity weakens.

## 5. How does the mass of an object affect the gravitational force?

The mass of an object directly affects the gravitational force it exerts on other objects. The greater the mass, the greater the gravitational force. This can be seen in the equation for universal gravitation, where the force is directly proportional to the product of the masses of the objects.

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