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March 6, 2015

March 6, 2015

Posted by **john** on Tuesday, February 28, 2012 at 11:08pm.

Earth Radius = 6.37x10^6 m

Moon Radius = 1.74x10^6 m

Jupiter Radius = 1.90x10^7 m

Earth to moon distance = 3.84x10^8 m

earth to sun 1.496x10^11m

jupiter to sun 7.78x10^11 m

(a) The Earth and the Moon. Give the answer as a fraction of the earth's radius.

(b) The Sun and the Earth. Give the answer as a fraction of the sun's radius.

(c) The Sun and Jupiter. Give the answer as a fraction of the sun's radius.

please show how to get it i am really stuck.

- Physics Please help! -
**Steve**, Wednesday, February 29, 2012 at 11:25amJust think of the planets as point masses on a lever. We want the lever to balance, where the fulcrum is the center of mass.

So, m1d1 = m2d2

or, m1/m2 = d2/d1

For earth-moon,

d = 3.84x10^8 = d1+d2

earth mass = 5.9742x10^24

moon mass = 7.3477x10^22

m1/m2 = 81.307

so, 82.307 * d1 = 3.84x10^8

d1 = 4.7228x10^6

So, the center of mass for the earth-moon system is 4.7228x10^6m from the center of the earth.

4.7228x10^6/3.84x10^8 = 0.0123 of earth radius

do similar work for the other systems

- Physics -- PS -
**Steve**, Wednesday, February 29, 2012 at 11:27amOops. I figured as a fraction of the earth-moon distance, not the earth radius.

4.7228x10^6/6.37x10^6 = 0.74 of earth radius

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