问题 多选题

如图所示,两个带等量正电荷的小球A、B(可视为点电荷),被固定在光滑的绝缘水平面上.P、N是小球连线的中垂线上的两点,且PO=ON.现将一个电荷量很小的带负电的小球C(可视为质点),由P点静止释放,在小球C向N点运动的过程中,下列关于小球C的速度、加速度的图象中,可能正确的是(  )

A.

B.

C.

D.

答案

A、B在等量异种电荷连线中垂线上电场强度方向O→P,负点电荷q从P点到O点运动的过程中,电场力方向P→O,速度越来越大.但电场线的疏密情况不确定,电场强度大小变化情况不确定,则电荷所受电场力大小变化情况不确定,加速度变化情况无法判断.但是加速度随时间一定发生变化.

越过O点后,负电荷q做减速运动,则点电荷运动到O点时速度最大.电场力为零,加速度为零.

根据电场线的对称性可知,越过O点后,负电荷q做减速运动,加速度的变化情况无法判断.故A、D错误,B、C正确.

故选BC.

单项选择题
阅读理解

Massachusetts (美国一州名) became the first state in the nation to ban the dumping (倾倒;抛弃) of electronic equipment such as computer monitors and television sets. It means people there can no longer put computer monitors, TV sets and other devices containing glass picture tubes out on the street for pickup by garbage cleaners.

Official said much of this equipment is loaded with poisonous heavy metals such as lead, cadmium and mercury. These poisonous heavy metals could go into groundwater or be released (释放) into the air.

The Boston Globe reports the state has set up a system to recycle techno-garbage at state expense through community recycling centers.

Robin Ingenthron of the Massachusetts Department of Environmental Protection said the state has been trying to get its electronics-recycling program in place ‘before the future wave of electronics hits’. The National Safety Council estimates some 300 million computers will enter the nation’s waste system in the next few years.

In addition, millions of people will be getting rid of their old television sets. New high-quality digital televisions and new rules will make old TV sets no longer in use over the next several years.

小题1:The word ‘techno-garbage’ in the 3rd paragraph probably means ________.

A.all kinds of dirty things

B.deserted TV sets

C.heavy metals

D.used electronic equipment小题2:The passage tells us chiefly about __________.

A.forbidding of a certain type of garbage dumping

B.new problems of environmental protection

C.household problems raised by computers and TV sets

D.the handling of garbage小题3:     Which is NOT a reason that the state enforces (强制执行) a ban on electronic equipment dumping?

A.This kind of garbage is poisonous.

B.Recycling systems are not working well.

C.The poisonous heavy metals can go to the underground water and the air.

D.There will be much more electronic garbage soon.小题4: According to the last paragraph many people will be dumping their TV sets because ________.

A.they are broken

B.they are poisonous

C.new TV standards have come out

D.people will be tired of them