Finding the net gravitational force on a rocket....

In summary: Now use that along with the distance from the center of the Earth to find the net force on the rocket from both bodies.In summary, the Earth has a mass of 5.98 x 1024 kg, the moon has a mass of 7.35 x 1022 kg, and the distance between their centers is 3.84 x 108 m. A rocket with a mass of 1200 kg is located 3.0 x 108 m from the center of the Earth and is directly in between the Earth and the moon. The net gravitational force on the rocket can be found by using the equation Fnet = Gm1m2/r2, where m1 is the mass of the Earth,
  • #1
Specter
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Homework Statement


The Earth has a mass of 5.98 x 1024 kg and the moon has a mass of 7.35 x 1022 kg. The distance from the centre of the moon to the centre of the Earth is 3.84 x 108 m. A rocket with a total mass of 1200 kg is 3.0 x 108 m from the centre of the Earth and directly in between the Earth and the moon. Find the net gravitational force on the rocket from the Earth and the moon.

Homework Equations


Fnet = Gm1m2/r2

The Attempt at a Solution


m1 (earth)=5.98 x 1024 kg
m2 (moon)=7.35 x 1022 kg
m3 (rocket)=1200kg

m1 is 3.85 x 108m from the centre of m2
m3 is 3.0 x 108 m from the centre of m1

My problem is trying to figure out how far the rocket(m3) is from the moon(m2). The question says that the rocket is directly in between the Earth and the moon, so does that mean that the distance is 3.0 x 108 m to the centre of the moon and to the centre of the earth?

Next I would use Fnet = Gm1m3/r13 + Gm2m3/r23 and solve the question. In the example I read it said "add their magnitudes since both forces act in the same direction". In this question the forces would be acting in different directions, one toward the moon and the other toward earth. Does this mean I subtract the magnitudes instead of adding?
 
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  • #2
Specter said:
The question says that the rocket is directly in between the Earth and the moon, so does that mean that the distance is 3.0 x 108 m to the centre of the moon and to the centre of the earth?
It is saying that the rocket is somewhere on the line connecting the two centers. Not necessarily at the midpoint of that line.
Specter said:
Does this mean I subtract the magnitudes instead of adding?
That will give you the magnitude of the result. If you want to know its direction, you will have to decide which pull is stronger.
 
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  • #3
jbriggs444 said:
It is saying that the rocket is somewhere on the line connecting the two centers. Not necessarily at the midpoint of that line.

That will give you the magnitude of the result. If you want to know its direction, you will have to decide which pull is stronger.

The pull of the Earth would be stronger. So if the Earth's pull is stronger than the moons the rocket would be closer to the Earth than the moon, right? But how can I figure out the distance knowing this?
 
  • #4
Specter said:
So if the Earth's pull is stronger than the moons the rocket would be closer to the Earth than the moon, right?
The position of the rocket is what it is regardless of the force it is subject to.
 
  • #5
jbriggs444 said:
The position of the rocket is what it is regardless of the force it is subject to.
I think I figured it out. I was making it way harder then it needed to be...

3.84 x 108-3.0 x 108=8.4 x 107
 
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  • #6
Specter said:
I think I figured it out. I was making it way harder then it needed to be...

3.84 x 108-3.0 x 108=8.4 x 107
Yep. That's the distance of the rocket from the center of the moon.
 
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Related to Finding the net gravitational force on a rocket....

1. How is the net gravitational force on a rocket calculated?

The net gravitational force on a rocket is calculated by multiplying the mass of the rocket by the acceleration due to gravity at that location. This formula is represented as F = mg, where F is the net gravitational force, m is the mass of the rocket, and g is the acceleration due to gravity.

2. What factors influence the net gravitational force on a rocket?

The net gravitational force on a rocket is influenced by the mass of the rocket, the mass of the planet or object it is near, and the distance between the rocket and the planet or object. The force also depends on the strength of the planet's or object's gravitational field, which is determined by its mass and size.

3. How does the net gravitational force affect the motion of a rocket?

The net gravitational force affects the motion of a rocket by pulling it towards the center of the planet or object. This force is responsible for keeping the rocket in orbit around the planet or object, or for propelling it towards or away from the planet or object.

4. Is the net gravitational force the only force acting on a rocket?

No, the net gravitational force is not the only force acting on a rocket. Other forces such as air resistance, thrust from the rocket's engines, and the force of gravity from other nearby objects may also affect the motion of the rocket.

5. Can the net gravitational force on a rocket be negative?

Yes, the net gravitational force on a rocket can be negative if the force is acting in the opposite direction of the rocket's motion. This can happen if the rocket is moving away from the planet or object and the gravitational force is pulling it back towards the planet or object.

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