题目

如图所示，质量为m的木块在质量为M的长木板上滑动，长木板与水平地面间的动摩擦因数为μ1，木块与木板间动摩擦因数为μ2，已知长木板处于静止状态，那么此时长木板受到的地面摩擦力大小为（ ） A．μ2mg B．μ1Mg C．μ1（m+M）g  D．μ2mg+μ1Mg 答案：解：对小滑块受力分析，受重力mg、长木板的支持力FN和向左的滑动摩擦力f1，有 f1=μ2FN FN=mg 故f1=μ2mg 再对长木板受力分析，受到重力Mg、小滑块的对长木板向下的压力FN、小滑块对其向右的滑动摩擦力f1、地面对长木板的支持力FN′和向左的静摩擦力f2，根据共点力平衡条件，有 FN′=FN+Mg f1=f2 故 f2=μ2mg 故阅读A, B两篇短文, 从每小题所给的四个选项中, 选出能回答所提问题或完成所给句子的最佳答案, 并在答题卡上将该项涂黑. AKindle, Nook or Ipad? How should we choose the right e-book reader?KindlePrice: $139Weight: 289gPage Size: 6 inches (e-ink screen)In it there can be over 390,000 books to choose from. You can also read international newspapers and magazines. Click here for more.NookPrice: $148Weight: 196gPage Size: 6 inches (e-ink screen)It is similar to Kindle in many ways. The e-ink screen is muchbetter for eyes than the traditional computer or desk screen. Click here for more.Apple iPadPrice: $499Weight: 780gPage size：9.7 inches (Full-colour touch LCD screen)It can work as a tablet computer as well as an e-book reader. Many young people use it to watch videos. Click here for moreNookColorPrice: $249Weight: 448gPage Size: 7 inches (full-color touch LCD screen)It not only offers books, magazines and newspapers, but it can also be used as a video player. Click here for more【1】This passage probably comes from a ____________·A.textbookB.storybookC.newspaperD.website【2】Which e-book reader can be used to read books and watch videos?A.Kindle and Ipad.B.iPad and NookColor.C.Nook and Kindle.D.NookColor and Nook.【3】How much will David pay if he buys a Nook and a Kindle?A.$287.B.$385.C.$397.D.$647.【4】An e-reader with an e-ink screen is good for a student who ____________.A.loves colourful picturesB.loves computer gamesC.wants to protect their eyesD.wants to save money【5】In the four e-readers, Nook ____________.A.is the lightestB.costs mostC.has the largest page sizeD.can work like a computer