如圖所示,一只半球形碗倒扣在水平桌面上處于靜止?fàn)顟B(tài),球的半徑為R,質(zhì)量為m的螞蟻只有在離桌面高度大于或等于時(shí),才能停在碗上,那么螞蟻和桌面的最大靜摩擦力為( )                                                

                                                                                                 

  A. 0.6mg   B.      0.8mg      C. 0.4mg     D. 0.75mg

                                                                                                                                        

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