问题 选择题

质量为m的子弹在h=10m高处以800m/s的水平速度射出枪口,质量为M(已知M>m)的物体也在同一地方同时以10m/s的水平速度抛出(不计空气阻力),则有(  )

A.子弹和物体同时落地

B.子弹落地比物体迟

C.子弹因质量较小,水平飞行距离较短

D.无法确定

答案

子弹和物体都做平抛运动,竖直方向做自由落体运动,高度相同,根据t=

2h
g
可知子弹和物体运动时间相同,即同时落地,故A正确,BD错误;

C、水平方向都做匀速运动,子弹水平方向速度大于物体水平方向速度,时间相同,所以子弹水平飞行距离较大,故C错误

故选A

阅读理解

阅读下面短文,从各小题所给的四个选项中选出能够回答所提问题或完成所给句子的最佳答案。 

       Once upon a time there was an old farmer who had a horse which was almost as old as himself.    

One day, he set out one morning with his son to sell the horse before it died. Both father and son walked

because the farmer did not want the horse to be too tired.    

       On the way, they met two men who said, "Why are you walking, farmer? You have a horse. It's a

long way to market."'rhe farmer knew that this was true, so he rode on the horse while his son walked.

then they met two old women who said,"What are you doing up there, farmer? Can't you see how tired

the boy is?" So the farmer got down,’and then his son rode instead. Next, three old men stopped them,

and one old man said, "Why are you walking, farmer? Get up, it's too hot for an old man like you to walk

today.”So the farmer got up behind his son, and they rode on. Some time later,a young woman passed

them.  "Why aren't you walking?" she asked, "It isn't far to the market. Give your poor horse a rest."So

the farmer and his son got down once again. It is a fact that you cannot please all the people all the time.

1. The farmer wanted to sell the horse________.    

A. before it was dead              

B. before it became too tired    

C. before the market was over        

D. before it was as old as he was

2. The two men on the road________   .

A. asked how far it was to the market    

B. said they thought the liorse looked very tired    

C. dsked why the farmer was not riding on his horse    

D. told the farmer's son to get off the horse and walk

3. The two old women said it was wrong for____         .    

A. the farmer to ride such a tired horse    

B. the farmer to ride while his young son walked    

C. the boy to ride instead of his father    

D. only one person to ride such a long way

4. The f'armer got up behind his son because____           .    

A. the old man said it was too hot for him to walk    

B. the three old men stopped them on the road    

C. he dicl not know why he was walking    

D. his son could not ride the horse by himself

5. The yourig woman was most sorry____               

A. for the old man    

B. for the farmer's young son    

C. that it was not far to the market    

D. for the horse

单项选择题