题目

如图4-3-2所示的杆可绕O点转动，若保持杆处于图中所示的位置静止，可在A端分别施加力F1、F2、F3、F4，其中最小的力是_______. 答案：解析：杆可绕O点转动，对杆的转动有影响的是重力G和拉力F，由平衡条件可知： MF+MG＝0，即F·l-G·＝0，d为杆的长度，l为力F的力臂.要使作用在杆上的拉力F最小，则需F的力臂最大，因为F3的力臂最大，所以F3最小.听对话，根据对话内容完成下面的句子，每空词数不限。对话读三遍。听对话前，你们有20秒的时间阅读下列句子。【1】What was wrong with Peter? He _____________ the Chinese test and wanted to give it up.【2】Why can’t Peter ask his teacher for help? Because his teacher is _____________________.【3】What does Ann good at? She is good at Chinese and _________________.【4】What does Ann do on the weekends? She goes to the art club and does __________________ work on the weekends.【5】Where will Peter and Ann meet? They will meet at __________________ home.