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
| 交际用语。 | |
| A: 1______, boy? B: I think I have a cold. I feel terrible. A: 2______ B: No, my body temperature (温度) is all right. But I have a headache and a sore throat. A: Open your mouth and let me see. Oh, 3______ Please take the medicine on time, you'll be better soon. B: But I feel so bad, doctor. 4______ A: Don't worry. 5______ They are good for your health. | |
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