[題目] 南科高中教師甄試
[領域] 靜力學
[來源] 教師甄試
[題目] http://ppt.cc/M7Op
[瓶頸]
先把整個系統的圖畫出來可以知道左右兩端的拉力 http://ppt.cc/fWlp
再專門探討左段 假設左段長度x 質量為(x/L)Mg
利用左端點為支點 左段受到重力(x/L)Mg、拉力4/5Mg的力矩
重力力矩 = (x/2)(4/5)(x/L)Mg
拉力力矩 = (x)(4/5)Mg
所以(x/2)(4/5)(x/L)Mg = x(4/5)Mg
解得x = 2L
不知道錯在哪邊
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