问题
不定项选择
一质量为m的带电液滴以竖直向下的初速度V0进入某电场中。由于电场力和重力的作用，液滴沿竖直方向下落一段距离h后，速度变为零。以下判断正确的是[ ]
A．电场力对液滴做的功为
B．液滴克服电场力做的功为mg+
C．液滴的机械能减少mgh
D．液滴受到的电场力大于它的重力
答案
BD
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一质量为m的带电液滴以竖直向下的初速度V0进入某电场中。由于电场力和重力的作用，液滴沿竖直方向下落一段距离h后，速度变为零。以下判断正确的是[ ]
A．电场力对液滴做的功为
B．液滴克服电场力做的功为mg+
C．液滴的机械能减少mgh
D．液滴受到的电场力大于它的重力
BD
| 阅读下列图表，从每题所给的A、B、C三个选项中，选出最佳选项回答问题或完成句子。 | |||||||||||||||||||||
1. You can buy _____ kinds of fruits in Miss White's Fruit Store.  | |||||||||||||||||||||
[ ] | |||||||||||||||||||||
| A. four B. five C. six | |||||||||||||||||||||
2. How much are the pants?  | |||||||||||||||||||||
[ ] | |||||||||||||||||||||
| A. Twelve dollars. B. Thirteen dollars. C. Eighteen dollars. | |||||||||||||||||||||
3. Lily wants to speak English well. She can buy _____. | |||||||||||||||||||||
[ ] | |||||||||||||||||||||
| A. Skills for English Listening and Speaking B. 100 English Stories C. Learning English in Your Car | |||||||||||||||||||||
4. In the afternoon, _____ is Li Lei's first class.
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[ ] | |||||||||||||||||||||
| A. science B. music C. P.E. | |||||||||||||||||||||
5. The card doesn't show ______.  | |||||||||||||||||||||
[ ] | |||||||||||||||||||||
| A. the name B. the telephone number C. the address |