问题 多选题

如图所示的是杂技演员表演的“水流星”.一根细长绳的一端,系着一个盛了水的容器.以绳的另一端为圆心,使容器在竖直平面内做半径为R的圆周运动.N为圆周的最高点,M为圆周的最低点.若“水流星”通过最高点时绳子的拉力恰为mg,则下列判断错误的是(  )

A.“水流星”到最高点时的速度为零

B.“水流星”通过最高点时的速度v=

gR

C.“水流星”通过最高点时,水对容器底恰没有压力

D.“水流星”通过最高点时,水不可能从容器中流出

答案

A、B、“水流星”到最高点时,绳子的拉力恰为mg,对容器和水整体研究,重力和拉力的合力提供向心力,根据牛顿第二定律,有:

T+mg=m

v2
R
         ①

其中T=mg           ②

联立解得:v=

2gR
,故A错误,B错误;

C、D、再对水研究,受重力和容器的支持力,根据牛顿第二定律,有:

N+mg=m

v2
R

解得:N=mg

即容器对水有向下的支持力,大小为mg,故水对容器壁有向上的压力,水不会流出,故C正确,D错误;

故选ABC.

阅读理解

One day Mr. and Mrs. Black were driving to a party . Mr. Black drove the car very fast. “Please don’t drive so fast.” Mrs Black asked his husband to drive more slowly .”If you drive so fast , maybe we’ll have some trouble.”“Oh , no , Don’t be worried , my dear . ”said Mr. Black with a smile .“You know I’m good at driving . You won’t be in danger . And there is little time . If I don’t drive fast , we’ll be late for the party.”

A few minutes later , his wife , Mrs. Black , said to him,“If you don’t slow down ,We’ll be in hospital.”

Just at this moment a car came out of a side road and crossed in front of their car . Mr. Black stopped their car quickly . It nearly hit that car: “Oh , dear , I’m sorry for that . You are right , my dear,”said Mr Black . “I’ll never drive fast later . Now let me drive slowly . ”Then car drove very slowly to the party . Of course they were very late for the party.

小题1:Mr. and Mrs. Black were driving to ________ one day.

A.a meeting

B.their home

C.a party

D.work小题2:What did Mrs. Black ask her husband to do?      

A.To stop the car

B.To drive more slowly

C.To drive to a hospital

D.To drive fast小题3:Mr. Black drove so fast , because___________ .

A.he was good at driving

B.he was very happy

C.he was in danger

D.he didn’t want to be late for the party.小题4:What happened to them a few minute later ?       

A.Their car hit another car

B.their car nearly hit another car

C.Their car was broken

D.Something was wrong with their car小题5:At last Mr. Black drove their car ________  to the party

A.faster

B.slow

C.very slowly

D.happily

单项选择题