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Homework Help: Mass and radius

  1. Sep 3, 2008 #1
    1. The problem statement, all variables and given/known data

    I know this is a dumb question but if the radius of a planet is one-fifth of the earth's radius. what is the mass of the planet.

    Earth mass => 5.97 *1024
    earth radius => 6.38 *106

    3. The attempt at a solution

    my answer: 5.97 *1024(1/10)
    Last edited: Sep 3, 2008
  2. jcsd
  3. Sep 3, 2008 #2


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    Homework Helper

    And incorrect.

    If the radius is 1/5 and it has the same density as earth, then what would the mass be?

    Think about the ratio of the volume between the 2 and then multiply that appropriately by earth mass.
  4. Sep 3, 2008 #3
    Can u please give me more details.
  5. Sep 3, 2008 #4
    density = mass/volume --> [itex]\rho=m/v[/itex]

    What is the formula for determining the volume of a sphere? Given the earth's radius, what is its volume?
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