Net gravitational force on earth

AI Thread Summary
The discussion focuses on calculating the net gravitational force acting on a rocket located between the Earth and the Moon. Participants clarify the correct distances to use in the gravitational force formula, emphasizing that the rocket is directly aligned with both celestial bodies. It is confirmed that the gravitational forces from both the Earth and the Moon must be calculated separately and then combined to determine the net force. The importance of understanding the direction of these forces is highlighted, as gravity is an attractive force. Overall, the conversation aims to ensure accurate application of Newton's Law of Gravitation for the scenario presented.
fa08ti
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the Earth has a mass of 5.98 x 10^24 kg and the moon has a mass of 7.35 x 10^22 kg. the distance from the centre of the moon to the centre of the Earth is 3.84 x 10^8m. a rocket with a total mass of 1200kg is 3.0 x 10^8 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 moon.

ATTEMPT

ok so i used Fnet=( (Gm1m2)/r^2) + ( (Gm2m3)/r^2)

m1 would be the mass of earth, m2 is the mass of the rocket and m3 is the mass of the moon
what I'm confused about are the r values. for the first one i used 3.0 x 10^8 and for the second r value is subtracted 3.0 x 10^8 from 3.84 x 10^8m. is that correct?
i got a big number for the answer (2.30 x 10^9 N) so i want to make sure i understand how to do this
 
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Very close; there is only one error. Hint: think about the directions of the forces.
 
i was thinking i should subtract the values because the rocket is in the middle and since gravity attracts and doesn't repel. is that anywhere near logical?
 
fa08ti said:
i was thinking i should subtract the values because the rocket is in the middle and since gravity attracts and doesn't repel. is that anywhere near logical?

Yes you are correct
 
"a rocket with a total mass of 1200kg is 3.0 x 10^8 m from the centre of the Earth and directly in between the Earth and the moon."

Doesn't this mean that the rocket forms a triangle with the Earth and moon?
If so, would we not have to calculate the distance between the rocket and the moon, and then add the forces together to get the net gravitational force?

Or is the rocket directly in line with the Earth and moon...
 
Last edited:
ch_advanced said:
"a rocket with a total mass of 1200kg is 3.0 x 10^8 m from the centre of the Earth and directly in between the Earth and the moon."

Doesn't this mean that the rocket forms a triangle with the Earth and moon?
If so, would we not have to calculate the distance between the rocket and the moon, and then add the forces together to get the net gravitational force?

Or is the rocket directly in line with the Earth and moon...

" directly in between the Earth and the moon " would imply that all the 3 are on a straight line.
And yes, we would have to calculate distance b/w rocket and moon, though it is not at all difficult i suppose :D

And then we would simply use Sir Issac Newton's Law Of Gravitation.
 
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