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问题 选择题

如图所示，物体A静止在光滑的水平面上，A的左边固定有轻质弹簧，物体B以速度v向A运动并与弹簧发生碰撞，A、B始终沿同一直线运动，mA="2" mB。当弹簧压缩到最短时，A物体的速度为

A．0              B．v            C．v            D．v

答案

答案：B

题目分析：当弹簧压缩到最短时，两个物体速度相等，根据动量守恒定律有，解得.此时AB的速度都等于，选项B对。

填空题

Questions 9-13


·You will hearfive people giving reasons why children learn their mother tongue so well.
·Before you listen, read the list of statements, five of which are summaries of what they were saying.
·Then listen carefully and match the statements (A-F) with the people who said them (9-13) respectively.
·There is one extra statement that you don’t need to use. You will hear the passage twice.
9. Maggie: ______
  • A. The time of their learning the mother tongue is the most
    favorable of all.
    10. Cherry: ______
  • B. Children hear their native language spoken always in its
    genuine form.
    11. Mike: ______
  • C. Children have private lessons all the time to learn their mother
    tongue.
    12. Hazel: ______
  • D. Children hear their native language spoken in all possible
    situations.
    13. Jody: ______
  • E. Children have special teachers to teach them.
  • F. Children have flexible organs and sensitive ear.
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问答题 简答题

区别完全叶与不完全叶。
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