Universal Gratvitation Problems

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In summary: Our goal is to make the discussions useful for future students who may have the same questions, and that means leaving the threads visible and the posts unedited.In summary, the weight of an object on Earth's surface decreases as its distance from the center of the Earth increases, according to the equation F = (GmM)/r^2. For the first question, the object would weigh only 10 N when its distance from the center of the Earth is three times the Earth's radius. For the second question, the astronaut's weight would be 1/36th of his weight on Earth's surface when he moves to a height of 6 Earth radii above the Earth's surface.
  • #1
s-win
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1. An object weighing 90 N on the Earth's surface would weigh only 10 N when its distance from the center of the Earth is ____?



Do I solve for mass and try to find r?


2. An astronaut has a mass of 90 kg on the Earth's surface. If he moves to a height of 6 Earth radii above the Earth's surface, how much will be his weight?
 
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  • #2
s-win said:
1. An object weighing 90 N on the Earth's surface would weigh only 10 N when its distance from the center of the Earth is ____?



Do I solve for mass and try to find r?


2. An astronaut has a mass of 90 kg on the Earth's surface. If he moves to a height of 6 Earth radii above the Earth's surface, how much will be his weight?

Welcome to the PF.

I fixed your post up a bit, and moved it to Intro Physics. The Advanced Physics forum is for upper-division and graduate-level questions.

When you fill out the Homework Help Template, take care to post your text between the bold lines you are given, instead of trying to replace that text with yours. The HH Template lines should stay visible and bold, and your text that you fill out should be plain text without any bolding.

When you fill out the HH Template, you list the Relevant Equations and your Attempt at a Solution.

What is the Relevant Equation for your first question? You don't need to solve for any mass -- the answer is independent of the mass of the object they are asking about...

Please show your work now...
 
  • #3
I'm kinda lost since I only learned this lesson in less than an hour and I have a test tomorrow so... I don't know what equation to use?
 
  • #4
s-win said:
I'm kinda lost since I only learned this lesson in less than an hour and I have a test tomorrow so... I don't know what equation to use?

What is the equation that relates the force of gravitational attraction to the mass of the Earth and the mass of the object and the distance separating their centers of mass? It's pretty much the only equation that applies, and I'm pretty confident you were shown in in the lesson. If not, check wikipedia.org ...

We do not give out answers here at the PF. The Rules link at the top of the page is pretty clear about how we handle Homework Help. Please show your work...
 
  • #5
10N/90N = 1/9th of the force

1/9 = 1/r^2
 
  • #6
s-win said:
10N/90N = 1/9th of the force

1/9 = 1/r^2

You are on the right track. Hopefully that means you found the right equation. So the ratio of the two radii is __________, which means that the object would be how far away?
 
  • #7
3radii
 
  • #8
s-win said:
3radii

Correct. Is that the form of the answer they want, or do they want a quantitative number?
 
  • #9
berkeman said:
Correct. Is that the form of the answer they want, or do they want a quantitative number?

Just like that. I'm new to the website, what if I want to delete posts or adjust it to a different section?
 
  • #10
s-win said:
Just like that. I'm new to the website, what if I want to delete posts or adjust it to a different section?

Just click the Report button on your post and ask the Mentors to help. Ignore the messsage that says Reports are only for spam, etc. That's how you ask for help from the Mentors.

Keep in mind that we do not delete posts or threads that have replies.
 

1. What is the formula for universal gravitation?

The formula for universal gravitation is F = G * (m1 * m2) / r^2, where F is the force of gravity, G is the gravitational constant, m1 and m2 are the masses of the two objects, and r is the distance between the two objects.

2. How is universal gravitation different from Earth's gravitational pull?

Universal gravitation refers to the force of attraction between any two objects in the universe, while Earth's gravitational pull specifically refers to the force of attraction between objects on Earth and the Earth itself.

3. Can universal gravitation be negative?

Yes, universal gravitation can be negative if the two objects are repelling each other instead of attracting. This can happen if the masses are of the same sign (both positive or both negative).

4. How does distance affect the force of gravity between two objects?

The force of gravity between two objects decreases as the distance between them increases. This is described by the inverse square law, which states that the force is inversely proportional to the square of the distance between the objects.

5. Can universal gravitation be used to explain the motion of planets?

Yes, universal gravitation is a fundamental force that plays a key role in the motion of planets. The gravitational force between the Sun and the planets is what keeps them in orbit around the Sun.

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