问题 选择题

如图所示,用绝缘材料制作的小车静止在水平面上,A、B是固定在小车上的两个金属板,两板间距离为L,分别带上等量异种电荷,两板间形成场强上为E的匀强电场.另有一个带电量为+q的小球从靠近A板处由静止释放,在电场力的作用下小球与B板相碰,碰撞后不反弹.小球的体积不计,所有接触面均光滑,下列说法中正确的是(  )

A.最终小车与小球一起在水平面上做匀速运动

B.在此过程中电场力对小球做功为EqL

C.小球获得的最大动能小于EqL

D.小球与小车系统增加的电势能为EqL

答案

A、据题,在电场力的作用下小球与B板相碰,碰撞后不反弹,小球与小车有共同的速度,根据系统的动量守恒得知,共同速度为零,最终小车与小球一起静止.故A错误.

B、C在小球在电场力作用下向右运动的过程中,小车在电场力作用下会向左运动,所以小球相对地面的位移小于L,电场力对小球做功小于EqL,根据动能定理得知,小球获得的最大动能小于EqL.故B错误,C正确.

D、由于电场力做正功,系统的电势能减小.故D错误.

故选C

阅读理解

Science Daily—Kids may roll their eyes when their mothers asks them about their school day, but answering her may actually help them learn. New research from Vanderbilt University reveals that children learn the solution to a problem best when they explain it to their mom.

“We knew that children learn well with their moms or with a peer, but we did not know if that was because they were getting feedback and help,” Bethany Rittle-Johnson, the study’s lead author and assistant professor of psychology at Vanderbilt’s Peabody College of education and human development, said. “In this study, we just had the children’s mothers listen, without providing any assistance. We’ve found that by simply listening, a mother helps her child learn.”

Rittle-Johnson believes the new finding can help parents better assist their children with their schoolwork, even when they are not sure of the answer themselves. Although the researchers used children and their mothers in the study, they believe the same results will hold true whether the person is the child’s father, grandparent, or other familiar persons.

“The basic idea is that it is really effective to try to get kids to explain things themselves instead of just telling them the answer,” she said. “Explaining their reasoning, to a parent or perhaps to other people they know, will help them understand the problem and apply what they have learned to other situations. We saw that this simple act of listening by mom made a difference in the quality of the child’s explanations and how well they could solve more difficult problems later on.

小题1:According to the passage, a mom had better ________.

A.give a kid some help when he is explaining his problem

B.just listen while a kid is explaining his problem

C.work together with a kid toward the solution to a problem

D.leave a kid alone when he meets a problem at school小题2: If she wants to help a child with his schoolwork, a mom ________.

A.should know the answer to a problem first

B.should pay attention to the child’s feedback.

C.may not know the answer herself

D.should not interrupt the child小题3:Who will be the least help to a kid when he is explaining, according to Rittle-Johnson?

A.The kid’s mom.

B.The kid’s grandmother.

C.A peer.

D.A relative the kid doesn’t know.小题4:Which of the following best gives the main idea of the passage?

A.Children learn better when their mom is hearing their explaining.

B.Children learn better if they find the solution to a problem themselves.

C.Parents should not provide any assistance to their children’s schoolwork.

D.A mom should listen more to their children when they have problems at school.

单项选择题