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Universal Gravitation and mass

  1. Dec 5, 2006 #1
    1. The problem statement, all variables and given/known data
    mass of star = 2.53 x 1030 kilograms
    mass of planet = 5.25 x 1024 kilograms
    mass of moon = 8.09 x 1022 kilograms
    average distance from star to planet = 1.14 x 1011 meters
    average distance from planet to moon = 4.59 x 108 meters

    Use the data above to determine the net force exerted on the moon by the planet and the star during:
    a. a solar eclipse.
    WebAssign will check your answer for the correct number of significant figures. wrong check mark N
    b. a lunar eclipse.
    WebAssign will check your answer for the correct number of significant figures. wrong check mark N


    2. Relevant equations
    Fg=G x M1 x M2/Dsquared
    Note that the lineup for a solar eclipse is Sun-Moon-Earth
    A lunar eclipse lineup is Sun-Earth-Moon
    This I am sure of.

    3. The attempt at a solution
    My attempt was to find the netforce of gravity on the moon.
    Here is my work which produced a wrong answer.
    a) Fgrav,net=Gm(moon)M(sun)/Dsquared(the distance between the star and the planet- the distance between the planet and the moon) - GM(moon)M(earth)/dsquared
    Perhaps I added the distances wrong- but I know when the moon is in the middle I will have opposite signs for the forces from each planet and the lunar eclipse should produce. I got 9.18E20 rounded for my answer to part a. Any ideas? Am i using the distance wrong? Any similar answers? Any other forces to be accounted for in the net sum? Thanks.
     
  2. jcsd
  3. Dec 5, 2006 #2

    berkeman

    User Avatar

    Staff: Mentor

    It looks like you are using the correct approach. Can you write out your math steps to make it easier to check them?
     
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