如图所示，一个带负电的油滴以初速度v0从P点倾斜向上进入水平方向的匀强电场中,若油滴到达最高点C时速度大小仍为v0，则油滴最高点的位置在( )
A．P点的左上方
B．P点的右上方
C．P点的正上方
D．上述情况都可能
答案：A
题目分析：对粒子受力分析知，粒子在重力与电场力作用下运动，直到运动到最高点，此过程初动能与末动能已知且相同，设粒子升高的高度为h，粒子的初末位置间的电压为UPQ，粒子的带电量为-q，由动能定理得：-qUPQ-mgh=0，解得：UPQ=-
；由于UPQ＜0，即UP＜UQ，说明Q点的电势高于P点，即带电粒子应在P点的左上方，故A正确．
| 阅读下面的对话，指出能填入相应空白处的最佳答案。 | ||||
| A：What's the 1 today, Mary? B：It's May 21st. A：Oh, tomorrow is your mom's birthday. Do you 2 ? B：Of course, I do. How shall we celebrate it? A：First of all, a birthday present. What about 3 her a beautiful sweater? B：That's a good idea. I think it will make 4 happy. A：Er… shall we have a special dinner? B：Yes, Dad. How about a Chinese dinner? A：OK, I'm going to buy a sweater. You can cook at home. B：Oh, don't forget to buy a 5 . A：Certainly. | ||||
|