问题 计算题

质量为m的小球从某一高处水平抛出,其初速度为,落地时速度为,不计空气阻力,求

(1)小球在空中飞行的时间(2)小球抛出点离地的高度。

答案

(1)(2)

解:(1)由平抛运动规律:有 ----2分

------2分  ------2分

故小球在空中飞行的时间为:----2分

(2)由于小球在竖直方向做自由落体运动,则

小球抛出点离地高度为:-----4分

本题考查的是平抛运动及自由落体运动的问题,根据平抛运动规律计算出飞行时间;根据自由落体运动计算出离地的高度;

阅读理解与欣赏
阅读理解

阅读理解。

     More than 6,000 children were expelled (开除) from the U. S. schools last year for bringing guns and

bombs to schools, the U. S. Department of Education said on May 8.   

    The department gave a report on the expulsions (开除) as saying handguns accounted for 85 percent

of the 6,093 expulsions in 1996-97, against 7 percent for rifles (步枪) or shotguns and 25 percent for other

types of firearms.   

    "The report is a clear sign that our nation's public schools are cracking down (严惩) on students who

bring guns to school." Education Secretary Richard Riley said in a statement. "We need to be tough-minded

about keeping guns out of our schools and do everything to keep our children safe."   

    In March 1997, an 11-year-old and a 13-year-old boy using handguns and rifles shot dead four children

and a teacher at a school in Jonesboro, Arkansas. In October, two were killed and seven wounded in a

shooting at a Mississippi school. Two months later, a 14-year-old boy killed three high school students and

wounded five in Daducah, Kentucky.   

    Most of the expulsions, 56 per cent, were from high schools, which have students from about age 16.

Nearly 34 per cent were from junior high schools and 9 per cent were from elementary schools, the report

said.

1. From the first paragraph we can infer that in the U. S. schools _____. [ ]

A. students enjoy shooting     

B. students are eager to be soldiers   

C. safety is a problem       

D. students can make guns

2. The report from the U. S. Department of Education shows that _____. [ ]

A. the number of the expulsions is not large   

B. the number of the expulsions is wrong   

C. there are soldiers hiding among the students   

D. guns are out of control in the U. S. schools.

3. The main idea of Paragraph 4 shows us _____. [ ]

A. some examples of shooting in the U. S. schools   

B. the American's feeling   

C. some terrible accidents   

D. that some teachers were killed by students

4. According to the passage, how many students were shot dead in 1997 in the U. S. schools? [ ]

A. 10    

B. 9   

C. 12    

D. 22