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Suppose the mass of the Earth were doubled (Physics 12)

by StaticWaffles
Tags: doubled, earth, mass, physics, suppose
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StaticWaffles
#1
Feb18-13, 07:25 PM
P: 8
1. The problem statement, all variables and given/known data
Suppose the mass of the Earth were doubled , but it kept the same density and spherical shape. How would the weight of objects at the Earh's surface change?


2. Relevant equations
Fg=Gm1m2/r^2


3. The attempt at a solution
g=G2m/r^2
g=19.59817612

g/g(on earth - 9.8)
=2

I know this is wrong because the textbook says the answer is 1.26 or 2^1/3.
I have no idea how to get this answer. I did find an online solution but they used equations that I have not been taught.

Here is a link to the online solution:
http://archives.evergreen.edu/webpag...HW/G6solns.pdf

If anyone can explain how to get this answer step by step that would be great.
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Simon Bridge
#2
Feb18-13, 10:00 PM
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If you double the mass, but keep the same density, what happens to the radius?
StaticWaffles
#3
Feb18-13, 10:48 PM
P: 8
It would increase?

Simon Bridge
#4
Feb19-13, 07:34 AM
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Suppose the mass of the Earth were doubled (Physics 12)

Did you increase the radius in your calculation?
StaticWaffles
#5
Feb19-13, 08:53 AM
P: 8
No I didn't. So it would double as well?
Simon Bridge
#6
Feb19-13, 08:56 AM
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Would it?
What is the relationship between mass and volume? volume and radius for a sphere?
StaticWaffles
#7
Feb19-13, 06:46 PM
P: 8
I get it now. My Physics teacher explained it to me after school. Thank you!
Simon Bridge
#8
Feb19-13, 07:52 PM
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Cool. Of course it would have been better if you'd reasoned it out yourself.
If you posted the answer here, you'd help someone else stuck on the same problem...?


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