问题
选择题
| 如图所示，AB是一质量为m的均匀细直杆，A端靠在光滑的竖直墙壁上，B端置于水平地面上，杆身与竖直方向夹角为θ，杆与地面的摩擦系数为μ，保持平衡，则此时杆与地面的摩擦力为（ ） A． B． C． D．μmg  |
mgtgθ
mgsinθ
答案
答案：A
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| 如图所示，AB是一质量为m的均匀细直杆，A端靠在光滑的竖直墙壁上，B端置于水平地面上，杆身与竖直方向夹角为θ，杆与地面的摩擦系数为μ，保持平衡，则此时杆与地面的摩擦力为（ ） A． B． C． D．μmg |
答案：A
| 从方框中选出最佳选项完成下面的对话。 | |
B: Thank you. A: Here is a table for two. 1_______ B: Thank you. May I have the menu, please? A: OK. Here it is. (A few minutes later) 2_______ B: Sure. We'll have Beijing Roast Duck and vegetable soup. A: 3_______ B: Yes. Two cups of coffee, please. A: Anything else? B: 4_______ A: OK. Thank you for your order. B: (Forty minutes later) May I have the bill, please? A: Let me see. 5_______ B: Here you are. |