问题 单项选择题

质点是理想化模型。下列实例中,能把研究对象视为质点的是()

A.研究地球绕太阳的运动规律

B.研究地球的昼夜交替规律

C.乒乓球运动员在针对对手的弱点采取削球时的乒乓球

D.研究一列火车通过南京长江大桥所需的时间

答案

参考答案:A

解析:如果一个物体的大小和形状对所研究的问题没有影响或影响很小以至于可以忽略时,我们就可以把这样的物体称做质点;地球绕太阳公转的过程中,地球的大小相对于地日间的距离而言很小,以至于可以忽略,所以可以看做质点,所以选项A正确;自转不可以看做质点,不然无法进行研究,所以选项B错误;同理可知选项C错误;在研究火车通过大桥的时间时,车长相对于大桥并不能忽略其长度,所以不能看做质点,所以选项D错误

填空题

短文填词

Dear Jack,

     I am writing to invite you to the fashion show to be held in

our school hall this Wednesday on 20th June to r________                                                    1.________

awareness of environmental________(保护) among                                                              2.________

middle school students.All the clothing in the show will

be m________from waste products,                                                                                     3.________

________as used newspapers,plastic packaging                                                                    4.________

bags,rubbish bags,and some o________waste.                                                                      5.________

Moreover,the fashion show will have v________of                                                                6.________

themes.There you will surely be able to see colorful

________(风格) and fashionable designs.I believe                                                                7.________

the show won't be________(失望) as all the                                                                        8.________

designers are required to combine fashion________                                                              9.________

the theme "A green world." What might s________                                                              10._______

you is that all the designers are coming from our school!

     If you are interested,call me before this weekend!

                                                  Yours,

                                                     Lily

问答题