问题 选择题

是某电场线上的两点,如图甲所示。一带负电的质点只受电场力的作用,沿电场线从点运动到点。在这个过程中,此质点的速度一时间图象图如乙所示,比较两点电势,的高低以及场强的大小,正确的是

A.

B.

C.

D.

答案

答案:B

本题考查电场强度;电势。解答本题关键是根据速度时间图象得到速度和加速度的变化情况,然后得到电场力的大小和方向情况,最后判断电势的高低。速度时间图象的切线的斜率表示加速度,从速度时间图象可以看出加速度恒定,电场力恒定,电场强度恒定,物体从a到b做匀减速运动,电场力方向向左。又因带负电的质点受到的电场力方向为场强的反方向,场强方向向右,电场线方向向右,顺着电场线方向,电势降低,所以 , 故B正确。

因此选B。

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     Getting your children to study can be a little like getting them to eat their vegetables.

     __1__ Make a study time and have it at the same time every day.This will help your kids to learn to

schedule their day and will give them a sense of control over how they spend their time.

     Allow them to study in blocks of time, such as for half an hour with a fiveminute break in the middle.

__2__ Ideal(理想的) study times are after dinner or right after school before dinner.

     Never allow your children to study in front of the television, as that will encourage passive activity.

__3__

      You'll also need to help your kids find the right place to study.After you've set up a good study time

for little learners, set up a good place where they can get those creative juices flowing.

     __4__ Make sure there is a table or a desk and a comfortable chair.

     __5__ This includes helping them out with their homework sometimes and being there for them with

the answers to any questions. The input you give your children during study periods will help form a bond

and help make studying enjoyable.

A. Pick a place where your children can study properly.

B. Hold them to the schedule they create for themselves.

C. Finally, spend time with your kids when they're studying.

D. Keep the atmosphere light and offer lots of encouragement, too.

E. Instead, use TV as a treat or a reward when the homework is completed.

F. Try to stop this bad habit by offering some sort of reward.

G. One of the best ways to form good study habits for your kids is to design a schedule that they keep to.