试题与答案

如图一个铁球从竖立在地面的轻弹簧正上方某处自由下落,接触弹簧并将弹簧压缩,在压缩

题型:选择题

题目:

如图一个铁球从竖立在地面的轻弹簧正上方某处自由下落,接触弹簧并将弹簧压缩,在压缩的全过程中,弹簧均为弹性形变,那么当弹簧压缩量最大时

A.球所受合力最大,但不一定大于重力值

B.球的加速度最大,且一定大于重力加速度值

C.球的加速度最大,有可能等于重力加速度值

D.球所受弹力最大,该弹力大于1倍重力值小于2倍重力值

答案:

答案:B

铁球下落过程中,刚接触弹簧时,仅受重力作用,加速度为重力加速度值,弹力逐渐增大,铁球做加速度逐渐减小的加速运动,当重力与弹力平衡时,加速度为零,速度达到最大值,然后铁球继续下落,弹力继续增大,铁球做加速度逐渐增大的减速运动,弹簧压缩量最大时,速度为零,加速度达到最大值,根据对称性,此位置比刚接触弹簧时加速度大,即球的加速度一定大于重力加速度值,弹力大于2倍重力值,故AC错误B正确D错误

故选B

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题型:阅读理解

阅读理解。

      Different job choices

      Many students have already had clear ideas about what jobs they would like to have in the future. We believe

boys' choices are different from girls'. To find out how different their choices are, we made a survey in Green

High School. The following diagram (图表) shows the results of the survey.

 

1. The diagram shows the results of ______ job choices in Green High School. [ ]

A. the teachers'

B. the boy and girl students'

C. the girl students'

D. the boy students'

2. About 45%of the girls would like to be _______ in the future.  [ ]

A. bank clerks

B. reporters

C. teachers

D. scientists

3. About _______ of the boys want to be teachers. [ ]

A. 5%

B. 15%

C. 30%

D. 50%

4. There are _______ number of girls want to be scientists.[ ]

A. large

B. the largest

C. the smallest

D. small

5. Which of the following sentences is RIGHT? [ ]

A. Gifts would like to be reporters more than boys.

B. Boys would like to be bank clerks more that girls.

C. Boys would like to be reporters most.

D. Girls would like to be teachers least.

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