Find Radius to Calculate Mass of Moon

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Homework Help Overview

The discussion revolves around calculating the mass of the moon based on the orbital parameters of the Apollo 8 capsule, which orbits at a height of 112 km above the lunar surface with a period of 120.5 minutes. The original poster is attempting to determine the correct radius needed to calculate the velocity for this mass calculation.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to use the formula for velocity in circular motion but is struggling with determining the correct radius. Some participants question whether the radius of the orbit should include the height above the moon's surface, while others suggest checking unit conversions.

Discussion Status

The discussion is ongoing, with participants providing hints and questioning assumptions about the radius and unit conversions. There is no explicit consensus yet, but some guidance has been offered regarding the calculation of the orbital radius.

Contextual Notes

There is a mention of potential confusion regarding unit conversions between kilometers and meters, which may affect the calculations. The original poster has expressed uncertainty about their previous calculations and the values used.

ucdawg12
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Okay, I'm having some trouble getting radius I need for the velocity that I need to solve this problem:

The manned Apollo 8 capsule was put into circular orbit 112km above the surface of the moon. The period of the orbiting space capsule was 120.5 minutes. If the radius of the moon is 1.74x10^6m, what is the mass of the moon.

Now I know how to find the mass of the moon once I get the velocity, but for some reason my velocity is coming out all wrong. I am doing v=2(pi)r/T, I know T=120.5x60= 7230seconds but I can't figure out how to find the radius. I have in my notes its 1850000m but of course I left out how I got to that and I think I have tried every combonation of numbers I have and still can't get it.

Thanks
 
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Isn't the radius of the orbit just 1.74 x 10^3 + 112 km?
 
omfg... i could have sworn those were first numbers I tried, I must have messed up somewhere on the calculator...
thanks, and sorry
 
Last edited:
Hehe :smile:. I guess you might not have converted the 112 km into metres, or the Moon's radius into km?
 
Well,Nylex,i'm surprised you haven't suggested him how to solve the problem...

Think that the gravity force (exerted by the moon on the satellite) is a centripetal force...

Daniel.
 

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