1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Consider a planet in some solar system which has a mass double

  1. Nov 9, 2011 #1
    1. The problem statement, all variables and given/known data
    Consider a planet in some solar system which has a mass double the mass of earth and same density as of earth . What is the weight of object on the planet in terms of 'W' , where 'W' is weight of object on Earth

    2. Relevant equations
    W=mg ... density = M / V . .... g=GM/R2

    3. The attempt at a solution
    since they both have same density..
    i equated their M/V ratios and it gets me the ratio of their radii ..
    but it still gets me nowhere
  2. jcsd
  3. Nov 9, 2011 #2


    User Avatar
    Gold Member

    Re: Gravitation

    Letting 'D' indicate the information you know for the double sized planet, you know

    [itex]M_{D} = 2M_{Earth}[/itex]

    and you know [itex]R_{D} = X R_{Earth}[/itex] where X is whatever you determined the ratio between the radii are. So simply find what the gravitational acceleration on this new planet will be with [itex]g = {{GM}\over{R^2}}[/itex]. The trick will be being able to write 'g' as [itex]g = Y \times {{GM_{Earth}}\over{R_{Earth}^2}}[/itex] where you have some constant, 'Y', multiplying the original values known for the Earth. Those known values you know gives [itex]g_{Earth} = 9.8 m/s[/itex].

    You'll have some multiplicative value in front that will tell you how many times stronger or weaker the gravity is.
  4. Nov 9, 2011 #3
    Re: Gravitation

    thanks , got it
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook