题目

English is one of the important subjects. And there are many ways for us to learn it well. But I think it is not easy to do so. We must try our best.    Everyone wants to remember all the vocabularies. We also want to use them correctly. Of course, we cannot expect to do this in a few months. We must read and write every day. We must study grammar. And we must practice more. The more you speak, the better your English will become.    Everyone can make mistakes when speaking. We should keep humorous when someone laughs at our mistakes. What we can do is just to speak more. As the ol某同学利用如图实验装置测量物体间的动摩擦因数，用弹簧测力计测得物体 A 重 40 N，物体 B重 20 N，按图组装好装置，物体 B 被水平力拉出 A 稳定后弹簧测力计读数为4.00N。（1）测得 AB 间的滑动摩擦力时 B 是否需要匀速拉出______ ？（选填需要或不需要）（2）测得 AB 间的动摩擦因数 1 为___________（3）若 B 与地面间的动摩擦因数 2 =0.4，水平拉力 F 至少为___________N。（最大静摩擦力等于滑动 摩擦力）