Question

如圖所示，杠桿處于平衡狀態，則F的力臂是
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               

A．OA

B．OC

C．OD

D．FD

Answer 1

B

試題分析：根據力臂的定義進行判斷；即力臂是從支點到力作用線的垂線段即可做出選擇．從圖中可以看出支點O到F作用線的垂線段為OC．其他線段，如OA、OD都與F的作用線不垂直，DF垂直OD，但與F的作用線不垂直，所以只有OC符合．
故選B．
點評：解決本題的關鍵是熟知杠桿五要素，重點對概念理解透徹，如力臂是支點作力的作用線的垂線段，不僅能從圖中讀出，同時還應該會畫出相應力的力臂．此題容易錯選D，注意：DF垂直OD，但與F的作用線不垂直．