绝缘水平面上静止着两个质量均为m、电荷量均为＋Q的物体A和B（A、B均可视为质点），它们间的距离为r
\u7edd\u7f18\u7684\u6c34\u5e73\u9762\u4e0a\u9759\u6b62\u7740\u4e24\u4e2a\u8d28\u91cf\u5747\u4e3aM\uff0c\u7535\u8377\u91cf\u5747\u4e3a+Q\u7684\u7269\u4f53A\u548cB\uff08A\uff0cB\u5747\u53ef\u89c6\u4e3a\u8d28\u70b9\uff09\u5b83\u4eec\u95f4\u7684\u8ddd\u79bb\u4e3aR\uff0c\u89e3\uff1a\u4f9d\u9898\u610f\uff0c3kQ^2/R^2<\u03bcmg<4kQ^2/R^2,\u8fd9\u6837\u5f00\u59cb\u8fd0\u52a8\u65f6\u7684\u77ac\u95f4\uff0c\u6bcf\u4e2a\u7269\u4f53\u53d7\u5230\u7684\u5408\u529b\u4e3a4kQ^2/R^2-\u03bcmg\uff0c\u968f\u540e\uff0c\u7531\u4e8e\u4e24\u4e2a\u7269\u4f53\u4e4b\u95f4\u8ddd\u79bb\u7684\u589e\u52a0\u7535\u8377\u65a5\u529b\u9010\u6e10\u51cf\u5c0f\uff0c\u8fd9\u662f\u4e00\u4e2a\u5408\u529b\u6216\u8005\u52a0\u901f\u5ea6\u9010\u6e10\u51cf\u5c0f\u7684\u52a0\u901f\u8fd0\u52a8\uff0c\u5f53\u5408\u529b\u51cf\u5c0f\u5230\u5927\u5c0f\u7b49\u4e8e\u03bcmg\u65f6\u52a0\u901f\u5ea6\u4e3a\u96f6\uff0c\u8bbe\u6b64\u65f6\u4e24\u7269\u4f53\u7684\u8ddd\u79bb\u4e3ar,\u5219\u6709
4kQ^2/r^2-\u03bcmg=0
r=2Q\u221a(k/\u03bcmg)
A\uff0cB\u8fd0\u52a8\u4e86\u7684\u8ddd\u79bb\uff08\u76f8\u7b49\u7684\uff09\u4e3a
(r-R)/2
=[Q\u221a(k/\u03bcmg)-R/2]
\u89e3\uff1a\u4f9d\u9898\u610f\uff0c3kQ\uff3e2\uff06\uff0347\uff1bR\uff3e2\uff06lt\uff1b\u03bcmg\uff06lt\uff1b4kQ\uff3e2\uff06\uff0347\uff1bR\uff3e2dhlp\u8fd9\u6837\u5f00\u59cb\u8fd0\u52a8\u65f6\u7684\u77ac\u95f4\uff0c\u6bcf\u4e2a\u7269\u4f53\u53d7\u5230\u7684\u5408\u529b\u4e3a4kQ\uff3e2\uff06\uff0347\uff1bR\uff3e2\uff0d\u03bcmg9517\u968f\u540e\u7531\u4e8e\u4e24\u4e2a\u7269\u4f53\u4e4b\u95f4\u8ddd\u79bb\u7684\u589e\u52a0\u7535\u8377\u65a5\u529b\u9010\u6e10\u51cf\u5c0f\u8fd9\u662f\u4e00\u4e2a\u5408\u529b\u6216\u8005\u52a0\u901f\u5ea6\u9010\u6e10\u51cf\u5c0f\u7684\u52a0\u901f\u8fd0\u52a89\u5f53\u5408\u529b\u51cf\u5c0f\u5230\u5927\u5c0f\u7b49\u4e8e\u03bcmg\u65f6\u52a0\u901f\u5ea6\u4e3a\u96f6jnrv\u8bbe\u6b64\u65f6\u4e24\u7269\u4f53\u7684\u8ddd\u79bb\u4e3ar\uff0c\u5219\u67094kQ\uff3e2\uff06\uff0347\uff1br\uff3e2\uff0d\u03bcmg\uff1d0r\uff1d2Q\u221a\uff08k\uff06\uff0347\uff1b\u03bcmg\uff09A\uff0cB\u8fd0\u52a8\u4e86\u7684\u8ddd\u79bb\uff08\u76f8\u7b49\u7684\uff09\u4e3a\uff08r\uff0dR\uff09\uff06\uff0347\uff1b2\uff1d\uff3bQ\u221a\uff08k\uff06\uff0347\uff1b\u03bcmg\uff09\uff0dR\uff06\uff0347\uff1b2\uff3d
解：依题意，3kQ^2/R^2<μmg<4kQ^2/R^2,这样开始运动时的瞬间，每个物体受到的合力为4kQ^2/R^2-μmg，随后，由于两个物体之间距离的增加电荷斥力逐渐减小，这是一个合力或者加速度逐渐减小的加速运动，当合力减小到大小等于μmg时加速度为零，设此时两物体的距离为r,则有 4kQ^2/r^2-μmg=0 r=2Q√(k/μmg) A，B运动了的距离（相等的）为 (r-R)/2 =[Q√(k/μmg)-R/2]绛旓細锛1锛夊A鍙楀姏鍒嗘瀽濡傚浘鎵绀猴紝鍥燗澶勪簬闈欐鐘舵侊紝鏁呮湁搴撲粦鍔汧澶у皬绛変簬闈欐懇鎿﹀姏f澶у皬锛屽簱浼﹀姏涓猴細F=k Q2r2鎵浠=F=k Q2r2锛2锛夊鏋滃皢鐗╀綋A鐨勭數鑽烽噺澧炶嚦+4Q锛屽垯涓ょ墿浣撳皢寮濮嬭繍鍔紝褰撳畠浠殑璺濈涓簉鈥=x锛漦Q2渭mg鏃讹紝鏈夊簱浠戝姏澶у皬F鈥=k4Q2r鈥2=4渭mg婊戝姩鎽╂摝鍔涘ぇ灏廸鈥诧紝f鈥=渭N=渭mg鍙堟湁...
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