题干

如图,粗糙水平面上a、b、c、d 四个相同小物块用四根完全相同的轻弹簧连接,正好组成一个等腰梯形,系统静止.ab之间、ac之间以及bd之间的弹簧长度相同且等于cd之间弹簧长度的一半,ab之间弹簧弹力大小为cd之间弹簧弹力大小的一半.若a受到的摩擦力大小为f,则(   )

A:ab之间的弹簧一定是压缩的

B:b受到的摩擦力大小为f

C:c受到的摩擦力大小为 3 f

D:d受到的摩擦力大小为2f

上一题 下一题 0.0难度 选择题 更新时间:2018-08-08 01:08:29

答案(点此获取答案解析)

A,B,C

同类题1

阅读理解

    READY or not, the college application season has begun. There are two main kinds of early admissions programs: Early Action and Early Decision.

    Early Action is a great choice for the well-prepared student. Students apply early, and are allowed to apply under an Early Action program to as many colleges as they choose. The biggest advantage for students is that colleges let them know early – in most cases, before Jan 1. Roughly 15 percent of colleges and universities offer an Early Action option(选择). Oct 15 is now the first deadline for many colleges and universities. This movement toward earlier deadlines is especially popular in the Southeast, with many of the large public universities leading the way. North Carolina State University, the University of South Carolina and the University of Georgia all have an Oct 15 Early Action deadline.

    Early Decision is a promise that cannot be reversed. Students who are accepted must take back their other applications and should attend that school. Students are allowed to apply to just one school under an Early Decision program. Early Decision deadlines are in early November, with colleges letting students know by mid-December. Many students believe that they are more likely to be accepted if they apply for Early Decision, but it actually depends.

       In some cases there is big increase in students being accepted, and at other colleges it is not that big at all. Generally, the strongest students are applying early. Athletes and students with focused interests are encouraged to apply for Early Decision.