Calculating Surface Gravity on Planet X?

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To calculate the acceleration due to gravity on planet X, which has a radius 2.2 times that of Earth and a density 2.5 times greater, one must first determine the mass using the relationship between density, volume, and mass. The volume of a sphere can be calculated with the formula V = (4/3)πr^3, where r is the radius. Once the volume is known, mass can be found by multiplying the volume by the density. Substituting this mass into the gravity equation g = GM/r^2 will yield the acceleration due to gravity on planet X. Understanding these relationships is crucial for solving the problem effectively.
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Homework Statement



Consider a hypothetical extra*solar world, planet X, that has 2.2 times the radius of the Earth and 2.5 times its density.

What is the acceleration due to gravity on the surface of planet X?


Homework Equations


g=GM/r^2



The Attempt at a Solution


I am not sure what to do with density. I know that mass/volume = density, but how do I solve the equation without mass? I know how to solve the equation when I know mass but if I only know density, how do I solve it?
 
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If you know the radius, you can calculate the volume. If you know the volume and the density, you can calculate the mass...
 
How do I use radius to calculate volume? What is the equation to do that?

Thanks
 
Thanks, I wasn't able to get it right but I appreciate your help!
 
Thread 'Correct statement about size of wire to produce larger extension'

Thread 'Correct statement about size of wire to produce larger extension'

The answer is (B) but I don't really understand why. Based on formula of Young Modulus: $$x=\frac{FL}{AE}$$ The second wire made of the same material so it means they have same Young Modulus. Larger extension means larger value of ##x## so to get larger value of ##x## we can increase ##F## and ##L## and decrease ##A## I am not sure whether there is change in ##F## for first and second wire so I will just assume ##F## does not change. It leaves (B) and (C) as possible options so why is (C)...
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