a hole on earth:

1)隻有一個地球,沒有其他影響.R=6400km.

石離地心x,以地心作無限個同xin球麵,僅小與X為半徑的球麵對石作用,可設質量在心,令石質量為m,球為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.

 

 

所有跟帖： 

• 又算錯,周期T約=85分. -jinjing- ♀ (0 bytes) () 09/14/2011 postreply 09:57:13

• 84 -guest007- ♂ (148 bytes) () 09/15/2011 postreply 09:56:00

• Thx, my earth radius is too long ,if it is 6370km,the answer is -jinjing- ♀ (59 bytes) () 09/15/2011 postreply 10:16:25

• 6370/6400*85=84 -jinjing- ♀ (0 bytes) () 09/15/2011 postreply 10:17:40

• More Math. -jinjing- ♀ (181 bytes) () 09/17/2011 postreply 07:14:05

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