题目

如图4所示，竖直直角墙上放有一杆AB，A处光滑，B处粗糙，试分析B处的静摩擦力方向. 答案：见解析【试题分析】 假设B处没有静摩擦力，那么B端将会水平向右滑动，因此可知B相对地面有向右的运动趋势，所以B处受到水平向左的静摩擦力作用.完形填空 (共10小题；每小题2分，满分20分) 阅读下面短文，掌握其大意，然后从21—30各题所给的A、B、C和D项中，选出最佳选项，并在答题卡上将该项涂黑。 Do you find getting up in the morning so difficult that it’s painful? This might be called   21  , but Dr. Kleitman has a new   22  . He has proved that everyone has a   23   energy cycle. During the hours when you   24   through your work you may say that you’re “hot”. That’s   25  . The time of day when you feel most   26   is when your cycle of body temperature is at its peak. For some people the   27   comes during the forenoon. For others it comes in the afternoon or evening. No one has discovered why this is so, but it   28   such familiar monologues as: “Get up, John! You’ll be late for work again!” The possible explanation to the trouble is that John is at his temperature-and-energy peak in the   29  . Much family quarrelling ends when husbands and wives   30   what these energy cycles mean, and which cycle each member of the family has. You can’t change your energy cycle, but you can learn to make your life fit it better. 21. A. patience     B. laziness       C. sadness        D. comfort 22. A. discovery    B. invention      C. explanation     D. statement 23. A. changing     B. increasing     C. full           D. daily 24. A. labour       B. get           C. go            D. look 25. A. honest       B. actual        C. true           D. real 26. A. pleasant      B. energetic     C. excited         D. comfortable 27. A. power       B. energy        C. peak           D. altitude 28. A. comes to     B. gets to        C. leads to        D. refers to 29. A. morning     B. afternoon      C. evening        D. noon 30. A. realize       B. recognize      C. memorize      D. see