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Quick gravitation problem?

  1. Dec 16, 2012 #1
    1. The problem statement, all variables and given/known data
    A spherical shell has inner radius R1, outer radius R2, and mass M, distributed uniformly
    throughout the shell. The magnitude of the gravitational force exerted on the shell by a point
    particle of mass m located a distance d from the center, outside the inner radius and inside the
    outer radius, is

    2. Relevant equations
    F = -GMm/r^2



    3. The attempt at a solution
    I know that from gauss's law that the force from a spherical shell would have the same gravitational force as one from a point particle. How would you find the gravitational force of a particle located between two shells though?
     
  2. jcsd
  3. Dec 16, 2012 #2
    any ideas
     
  4. Dec 16, 2012 #3

    haruspex

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    That's only true for points outside the shell. What is the force on a particle entirely inside the shell?
     
  5. Dec 16, 2012 #4
    0. Oh do you just find the force and use density = m/v to substitute m with pv.
    Then v = 4/3 pi r^3. Then u just subtract the total volume of the sphere by the volume of the sphere with distance d < the particle.
     
  6. Dec 16, 2012 #5

    haruspex

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    I'm not completely sure what you are saying there, but it doesn't sound quite right.
    Think of the given shell annulus as made up of two shell annuli: one with outer radius d and one with inner radius d.
     
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