问题 问答题

在绝缘水平面上放一质量m=2.0×10-3kg的带电滑块A,所带电荷量q=1.0×10-7C.在滑块A的左边l=0.3m处放置一个不带电的绝缘滑块B,质量M=4.0×10-3kg,B与一端连在竖直墙壁上的轻弹簧接触(不连接)且弹簧处于自然状态,弹簧原长S=0.05m.如图所示,在水平面上方空间加一水平向左的匀强电场,电场强度的大小为E=4.0×105N/C,滑块A由静止释放后向左滑动并与滑块B发生碰撞,设碰撞时间极短,碰撞后两滑块结合在一起共同运动并一起压缩弹簧至最短处(弹性限度内),此时弹性势能E0=3.2×10-3J,两滑块始终没有分开,两滑块的体积大小不计,与水平面间的动摩擦因数均为μ=0.5,g取10m/s2.求:

(1)两滑块碰撞后刚结合在一起的共同速度v

(2)两滑块被弹簧弹开后距竖直墙壁的最大距离s.

答案

(1)1.0m/s          (2)0.08m

(1)设两滑块碰前A的速度为v1,由动能定理有:

                                           

解得:v1="3m/s                                  "

AB两滑块碰撞,由于时间极短动量守恒,设共同速度为v

                              

解得:v="1.0m/s                                 "

(2)碰后AB一起压缩弹簧至最短,设弹簧压缩量为x1,由动能定理有:

      

解得:x1="0.02m                                     "

设反弹后AB滑行了x2距离后速度减为零,由动能定理得:

                    

解得:x2≈0.05m                                 

以后,因为qE>μ(M+m)g,滑块还会向左运动,但弹开的距离将逐渐变小,所以,最大距离为:S=x2+s-x1="0.05m+0.05m-0.02m=0.08m.                "

改错题

第一节,短文改错(共10小题;每小题1分,满分10分)

以下标有题号的每一行均有一个错误,请找出,并按下列情况改正;

此行多一个词;把多余的词用斜线(\)划掉,在该行右边横线上写出该词,并也用斜线划掉。

此行缺一个词:在缺词处加一个漏字符号(^),在该行右边横线上写出该加的词。

此行错一个词:在错的词下划一横线,在该行右边横线上写出改正后的词。

注意:请在答题卡上作答。

Here is my idea about bow a friend is like. Firstly,              76. ____________

a friend is somecone you can share your secrets. If you              77. ____________

tell himse secret, never will he talks about it with anybody            78. ____________

else. Besides, a friend is always good listener when you              79. ____________

need one. Afther hear your sad stories, he will say some              80. ____________

words that is nice and warm. Still, your happiness makes             81. ____________

him happily too. What’s more, a good friend is willing to             82. ____________

offer the help to which you need, or can at least give you            83. ____________

some advices, In a word, friends are those you like and               84. ____________

trust, and you will anioy every minute that. you spent with            85. ____________

them.

单项选择题