题干

如图所示,固定放置在同一水平面内的两根平行长直金属导轨的间距为d,其右端接有阻值为R的电阻,整个装置处在竖直向上磁感应强度大小为B的匀强磁场中.一质量为m(质量分布均匀)的导体杆ab垂直于导轨放置,且与两导轨保持良好接触,杆与导轨之间的动摩擦因数为μ.现杆在水平向左、垂直于杆的恒力F作用下从静止开始沿导轨运动距离l时,速度恰好达到最大(运动过程中杆始终与导轨保持垂直).设杆接入电路的电阻为r,导轨电阻不计,重力加速度大小为g.则此过程(   )

A:杆的速度最大值为 (Fμmg)Rd2B2

B:流过电阻R的电量为 BdlR+r

C:恒力F做的功与摩擦力做的功之和等于杆动能的变化量

D:恒力F做的功与安培力做的功之和大于杆动能的变化量

上一题 下一题 0.0难度 选择题 更新时间:2018-11-08 09:32:17

答案(点此获取答案解析)

B,D

同类题4

任务型阅读

                                                                                             Make the right choices

    What is life's greatest gift?____Choice is the ability to select one course of action from a set of alternatives to achieve a goal. What is so great about choice? It transforms us from dumb animals into artists. Each of us becomes another Michelangelo. Choice becomes nothing other than the tool we use to sculpt (雕刻)our life. The tool doesn't come free, however, for the price of choice is responsibility.____The reward is happiness.

    Life is not still. It is a flow.____We constantly need to monitor where we are on our journey. We need to ask questions: Am I moving closer to my goals? If not, what corrective measures can I take? What action will I take now to readjust myself to my goals? Choice is power. Choice is at the heart of life. It is the creative power of life.

    ____And your life becomes more convenient or comfortable because of them. For example, you decide which stores to shop at and which gas station to go to. But the decisions that we make to sculpt our lives are far more important than deciding where to shop. The more we appreciate the difference between minor and major decisions, the greater the probability that we will experience happiness and fulfillment.

    All chess lovers realize that it isn't necessary to win to enjoy the game. The pleasure is in the playing. Life is like a chess game.____

A. It is free will or choice

B. You have to make choices every day

C. Make the best moves you can under the circumstances

D. But when we accept and carry it out, we get a great return

E. Every choice we make leads us closer to or farther from our goals

F. Life is full of hard choices, and the bigger they are, the harder they get

G. Choose to carry out responsibilities not because you have to, but because you want to