Astronomy Basics: Solving Problems with Earth & Mars

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Homework Help Overview

The discussion revolves around two problems in astronomy related to orbital periods and gravitational attraction. The first problem involves calculating the orbital period of Mars using Kepler's third law, while the second problem focuses on determining the mass of a sphere based on gravitational force between two objects.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to apply Kepler's third law to find Mars' orbital period but expresses uncertainty about unit conversions and the resulting high values. They also question how to incorporate the gravitational force in the second problem and express doubt about their calculations.

Discussion Status

Participants are exploring the application of Kepler's laws and gravitational equations. Some suggest checking units and revisiting the calculations, while others express uncertainty about the results obtained. There is no explicit consensus on the correct approach yet, but guidance has been offered regarding the formulas to consider.

Contextual Notes

The original poster mentions confusion over unit conversions and the application of gravitational force in their calculations. There is also an indication that the results obtained seem unreasonable, prompting further inquiry.

vintagechic1251
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yes, i am defintely not a genius at this stuff...

i am having some problems figuring these two problems out:

Earth is 1.5x10^11 m from the Sun and has a period of 365.2 days. Mars is an average of 2.28x10^11 km from the sun. what is the orbital period of Mars in Earth years?

i am not exactly sure on what to do. should i convert m to km or the other way around? and i am not exactly sure on what equation to use either. i have used keplers third law to come out with an equation of the period of Mars is equal to the square root of the Earth's period squared times the radius of Mars over the radius of Earth cubed... i am getting really high answers like 5612 days and such. am i missing something?

i am also having problems with:

two spheres are 1.02 km apart. one of the spheres has a mass of 57.0 kg, and the force of attraction between the spheres is 1.79x10^-14 N. find the mass of the other sphere.

i'm not exactly sure on how to do that one because of the "force of attraction" i am not sure where i plug that value into. i have an equation of force times radius squared over gravitational force (6.67x10^-11) times the mass of the first sphere. and the answer i get when i do this is slightly unreasonable.

your help is greatly appreciated :smile:
 
Last edited:
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I'm not totally sure how to do the first part, but I'd check into Kepler's laws. You should take a look at your units too; perhaps you mean miles, not meters for Earth's radius of rotation.

For the second part, remember that the gravitational interaction between tow objects is found by:

F = (G*m1*m2)/r^2

G is a constant: 6.674E-11
 
Last edited:
seang said:
I'm not totally sure how to do the first part, but I'd check into Kepler's laws.

In particular the third one. :smile:
 
well i have done the third law and i get a really high answer which i am pretty sure can't be right.
 
vintagechic1251 said:
well i have done the third law and i get a really high answer which i am pretty sure can't be right.

Could you show us what you did?
 

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