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1. the gravitational field strength at the surface of the earth is 6 times its value at the surface of the moon. The mean density of the moon is 0.6 times the mean density of the earth.

I have volume earth x density earth = mass earth

& volume moon x density moon = mass moon

for mass earth

(4/3)PixR^3x0.6p=m

4/3xPixR^3xp=6m

(5/4)mp=PixR^3
(18/4)mp=PixR^3

3.6m1p1/m2p2=(r^3)/(r2^3)

appologies about the typing I got ratio of massxdensty=ratio of radius? The answer is 3.6 but I dont know how it relates to radius
2. you've probably done it already...

The field strength at the surface is proportional to m/r^2 so you get a r^3 factor in the mass on the top of each of your fraction (as you've been doing) and a r^2 on the bottom, which cancels to just an r on the top.

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Updated: April 17, 2013
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