问题
选择题
受水平外力F作用的物体，在粗糙水平面上作直线运动，其v-t图线如图所示，则
A．在0～t1秒内，外力F大小不断增大
B．在t1时刻，外力F为零
C．在t1～t2秒内，外力F大小可能不断减小
D．在t1～t2秒内，外力F大小一定不断减小
答案
CD
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受水平外力F作用的物体，在粗糙水平面上作直线运动，其v-t图线如图所示，则
A．在0～t1秒内，外力F大小不断增大
B．在t1时刻，外力F为零
C．在t1～t2秒内，外力F大小可能不断减小
D．在t1～t2秒内，外力F大小一定不断减小
CD
| 完形填空。 | ||||
| Dictionaries are very useful books. People use dictionaries to 1 out the meaning of words. If you are learning English, you would use an English dictionary. Some students have dictionaries. Their dictionaries contain (包含) Chinese and English words. They are useful, but it is usually 2 to use a dictionary written completely 3 English. This will help you to begin to think in English. A good English dictionary will show you the correct spelling of a word and its 4 . Many dictionaries also show 5 a word is used in sentences. | ||||
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