如图甲所示，闭合线圈固定在小车上，总质量为1kg．它们在光滑水_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题选择题

如图甲所示，闭合线圈固定在小车上，总质量为1kg．它们在光滑水平面上以10m/s的速度进入与线圈平面垂直、磁感应强度为B的水平有界匀强磁场，磁场方向垂直纸面向里．已知小车运动的速度v随车的位移x变化的v-x图象如图乙所示．则（　　）

A．线圈的长度L=15 cm

B．磁场的宽度d=15 cm

C．线圈进入磁场过程中做匀加速运动，加速度为0.8 m/s²

D．线圈通过磁场过程中产生的热量为48 J

答案

A．闭合线圈在进入和离开磁场时的位移即为线圈的长度，线圈进入或离开磁场时受安培力作用，将做减速运动，由乙图可知，L=10cm，故A错误；

B．磁场的宽度等于线圈刚进入磁场到刚离开磁场时的位移，由乙图可知，5-15cm是进入的过程，15-30cm是完全在磁场中运动的过程，30-40cm是离开磁场的过程，所以d=30cm-5cm=25cm，故B错误；

C．根据F=BIL及I=

BL v

R

得：F=

B2L2v

R

，因为v是一个变量，所以F也是一个变量，所以线圈不是匀加速运动，是变减速运动，故C错误；

D．线圈通过磁场过程中运用动能定理得：

1

2

mv₂²-

1

2

mv₁²=W_安，由乙图可知v₁=10m/s，v₂=2m/s，带入数据得：W_安=-48J，所以克服安培力做功为48J，即线圈通过磁场过程中产生的热量为48J，故D正确．

故选D

完形填空

Computer games are very popular. It is natural for people to want to _21___ , so playing against a computer or against a friend on the computer can be __22__to stop. “ Just one more game, ” often turns into another game, then another.
Computer games do have their _23__. They are excellent for training hand or eye coordination(协调).Surgeons (外科医生)_24____played computer games as children are often skilled. Computer games can __25__ be great for teaching students. The students are open to learning while playing. They can study for longer than a teacher would be able to teach.
But like anything __26__ in life, things should be balanced.(平衡).Too much time on the computer can _27__ your eyes. Regular breaks are needed. If students cannot _28__ playing computer games, they won’t do as well in other areas in their life—not just schoolwork, but in developing important social skill such as how to talk with people and how to work with others. And if they are no longer taking regular exercise, __29___ health will become worse.
Computer games have their place, __30___people must also remember it is important to have a balanced lifestyle.

B．suggestions

单项选择题

科学发展观的本质是以人为本，要以实现人的全面发展为目标。一切发展都是为了人，不断地满足人的需要、促进人的全面而自由地发展。离开了人的发展就失去了意义。人是发展的本质，是发展的出发点、落脚点。不坚持以人为本的发展是扭曲的、变态的发展。
这段话主要讲了：

A．科学发展观的本质：以人为本

B．树立科学发展观的必要性

C．科学发展观的概念

D．科学发展观的功能