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

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答案(点此获取答案解析)

A,B,C

同类题3

选择合适的选项补全短文。

Ways to Worry Less

    Do you want to worry less? Of course you do,fight? That's like me asking if I could send you free bacon.Worry is like black mold—it appears in damp conditions and spreads uncontrollably.And often times we don't realize it's there until it's killing us.We must get rid of worry before it destroys us.But how?____

    Do what you need to do.

    ____You ought not to avoid tough projects or hard conversions until the last moment.If you don't do what you should be doing,you will end up spending the rest of the time worried about the must-to-do things.Believe it or not, the anxiety that comes from worrying is much worse than the task we're worried about.____

    I think many of us act like we're puppets(木偶)in a play and we're waiting for something or someone to put us in the right place.You just react to whatever is going on.____We need to live on purpose.Nothing can cause worry like purposelessness.

    Make plans.

    You can't have intentionality without making plans.Making plan will enable you to achieve your aims more smoothly.Yet,don't place your plans in stone.You can adjust your plans flexibly.Accept changes.____

    There are other ways to lessen worry.As long as you are determined to take action,you will live a worry-free life.

A.Worry ruins creativity.

B.Get more intentional.

C.Do what you should be doing.

D.We need to stop letting life just happen.

E.Make new plans and then move forward.

F.You do the same as people around you do.

G.Here are some effective ways to deal with it.