问题 计算题

(17分)

如图17所示,固定的凹槽水平表面光滑,其内放置U形滑板N,滑板两端为半径=0.45m的1/4圆弧面,A和D分别是圆弧的端点,BC段表面粗糙,其余段表面光滑.小滑块P1和P2的质量均为m,滑板的质量M=4m.P1和P2与BC面的动摩擦因数分别为μ1=0.10和μ2=0.40,最大静摩擦力近似等于滑动摩擦力.开始时滑板紧靠槽的左端,P2静止在粗糙面的B点.P1以v0=4.0m/s的初速度从A点沿弧面自由滑下,与P2发生弹性碰撞后,P1处在粗糙面B点上.当P2滑到C点时,滑板恰好与槽的右端碰撞并牢固粘连,P2继续滑动,到达D点时速度为零.P1与P2视为质点,取g=10m/s2,问:

(1)P1在BC段向右滑动时,滑板的加速度为多大?

(2)BC长度为多少?N、P1、P2最终静止后,P1与P2间的距离为多少?

答案

(1)

(2)

(1)P1滑到最低点速度为,由机械能守恒定律有:

,解得:

P1、P2碰撞,满足动量守恒,机械能守恒定律,设碰后速度分别为

解得:=5m/s

P2向右滑动时,假设P1保持不动,对P2有:(向左)

对P1、M有:

此时对P1有:,所以假设成立.

(2)P2滑到C点速度为,由,得

P1、P2碰撞到P2滑到C点时,设P1、M速度为v,对动量守恒定律:

,解得:

对P1、P2、M为系统:

代入数值得:

滑板碰后,P1向右滑行距离:

P2向左滑行距离:

所以P1、P2静止后距离:

完形填空

Only Mother’s love is true love.It gives everybody everything in all her life.When you are a baby,mother takes good care of you as much as possible.In your waking hour,she always holds you in her arms.When you are ill,she stops her work to take you to see a doctor,and forgets about herself.When you are growing up day by day,she feels very happy .When you are old enough to go to school,mother is always encouraging you to study hard. she often tells you to put on more clothes on cold winter days.She always stands by the window waiting for you back from school.When you hurry to leave home for school without breakfast,she feels worried about you at home.When you do well at school,you will see her brightest smile on her face.Mother is always ready to give everything she has to her children,not to receive.What true love it is in the world! We shouldn’t forget Mother’s love where-ever we go or how old we are.

阅读短文,完成各题。

(一)划线部分提问。

小题1:she often tells you to put on more clothes on cold winter days.

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(二)同义句转换。

小题2:When you are a baby,mother takes good care of you as much as possible.

When you are a baby,mother  ____________  you well.

(三)请把该句子变为一般疑问句。

小题3:Mother is always encouraging you to study hard

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(四)根据短文内容简答问题。

小题4:When will you see your mother brightest smile on her face?

____________________________________________________

小题5:According to the writer’s words,what should we remember?

____________________________________________________

问答题 简答题