a hole on earth:

1)只有一个地球,没有其他影响.R=6400km.

石离地心x,以地心作无限个同xin球面,仅小与X为半径的球面对石作用,可设质量在心,令石质量为m,球为M,

We have mg=kmM/R^2,   stone"s force is kmM(x/R)^3/x^2=mg(x/R)=-ma=-md^2x/d^2t.We have d^2x/d^2t=-(g/R)x, x(t)=Acos(wt) w=(g/R)^.5=0.00124sec^(-1).T=808sec=13.47min.

Please chech it.

 

 

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