Sunday, 9 November 2014

P-Gravitation-02

2)A Uniform sphere has mass M and Radius R. Find the gravitational pressure P inside the sphere as a function of distance r from its center


3 comments:

  1. this is a really good question guys
    i would lyk u guys to try it before seeing the sol
    so therefore i will be posting it on 11th nov

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  2. The answer is 3GM^2/8piR^4 x [1-r^2/R^2].

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  3. Take a differential area dA at distance r from the center.

    Here, We take a cylindrical element of uniform cross section dA to Calculate Pressure.

    dF= -(GMr/R^3) x dm
    = -(GMr/R^3) x dA x dr x density
    = -[(GMr/R^3) x dr] x density x dA

    dF1= -density x dA x ∫_R^r(GMr/R^3) x dr (Here, dF1 is net force acting on surface at r radius)

    = (GM/2R^3) x density x dA x [ -r^2+R^2]

    Pressure= dF1/dA
    = (GM/2R^3) x density x [ R^2-r^2]
    =(GM/2R^3) x (M/V) x [ R^2-r^2]
    =(GM/2R^3) x (3M/4piR^3) x [ R^2-r^2]
    =(3GM^2/8piR^6) x [ R^2-r^2]
    =(3GM^2/8piR^4) x [1-r^2/R^2]

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