问题 计算题

如图所示,水平放置的M、N两平行板相距为d=0.50m,板长为L=1m,,两板间有向下的匀强电场,场强E=300.0N/C,紧靠平行板右侧边缘的 xoy直角坐标系以N板右端为原点,在xoy坐标系的第一象限内有垂直纸面向外的匀强磁场,磁感强度B=×10-2T,磁场边界OA与x轴夹角∠AOx=60°,现有比荷为×106C/kg的带电粒子(重力不计),沿靠近M板的水平线垂直电场方向进入电场,离开电场后垂直于OA边界进入磁场区域,

求:(1)带电粒子进入电场时的初速度v0;(2)带电粒子从进入电场到离开磁场的总时间。

答案

(1)  (2)

题目分析:(1)带电粒子要垂直射入磁场,则速度偏向角为30°

  (2分)

   (1分)

    (1分)

(2)粒子在电场中的运动时间为        (1分)

粒子在电场中的偏转距离为    (1分)

粒子离开电场的速度(1分)

粒子离开电场后做匀速直线运动,直线运动距离(2分)

运动时间(1分)

粒子进入磁场后的轨道半径为R,(2分)

(2分)由正弦定理有  

(2分)由此可知,带电粒子在磁场中的偏转角度为30°

由在磁场中的运动时间为(2分)

则总运动时间为(2分)

点评:带电粒子在电场中运动时关键是对其受力分析,根据牛顿第二定律解题,在磁场中运动时,需要画轨迹,定圆心,求半径,

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阅读理解

The main cause why some children are aggressive and are “always angry with the world ”is that they have no idea how to realize that the term “problem solving” does not necessary mean solving a math problem or an assignment. When you hear experts tell you to teach your children problem_solving skill, what they mean is to teach your kids all about emotional managing and learning to cross the stormy waters of childhood ,and eventually , life .

Parents should teach their children as early as possible how to handle certain situations . Young children easily lose their temper .When things do not go their way , it makes them angry and frustrated and they can get violent . Especially since young child have limited self control , bursting into anger is a very easy thing for them to do .

Anything can set up a child’s tantrum . For example , you and your child went to the mall . He told you that he wanted to buy a new toy , but you refused because he had already had one on his birthday. He insisted because this one was the new version . But you still refused , so he began to get angry and started screaming .

There are a few things that you can do to teach your child some problem _solving skills. First, you need to find out what the problem is . Perhaps your child is having problems identifying the cause of his frustrations . As a parent, it will not be that hard for you to know what is going on in your child’life. After he calms down, ask him quietly why he got so mad and then together , help him think why he was so angry . When your child figures out what is really making him upset , help him think of ways to solve the problem and help him look at all his reactions and evaluate the potential consequences.

小题1:who  would probably show interest in the passage ?

A, Experts      B, Teachers    C, Parents    D,Children

小题2:In paragraph 2 , the writer stresses that it is necessary for______________.

A, parents to guide their children  through troubling cases.

B, parents to solve some problems for their children

C, children to depend on their parents sometimes

D, children to manage bad situations as their parents do

小题3:In paragraph 3 the underlined word “tantrum” can be best replaced by “_________”

A, anger    B, habit    C, stress   D, aim

小题4:Which would be the best title for the passage ?

A, Taking  more care of your children.

B, Teaching  your children problem_solving skills.

C, What  are  problem_solving skills.

D, Why do your children become so  angry ?