问题 问答题

如图所示,质量为m的小球,以一定的速度进入半径为R、内径很小的光滑半圆管内,圆管竖直放置,小球通过最高点C时,对管壁上部的压力为3mg.

求:(1)小球在最高点C时速度的大小(2)小球落地点与最高点间的水平距离.

答案

(1)以小球为研究对象,小球通过最高点C时,根据牛顿第二定律得

      mg+N=m

v2C
R
,又N=3mg

得到,vC=2

gR

(2)小球离开最高点后做平抛运动,竖直方向做自由落体运动,则有

    2R=

1
2
gt2

则水平距离x=vCt=2

gR
?
4R
g
=4R

答:(1)小球在最高点C时速度的大小为2

gR
.(2)小球落地点与最高点间的水平距离4R.

完形填空
In China,a lot of food is wasted every year and the waste food is enough for        people. The food is wasted in restaurants, at home and in schools, etc.
In restaurants or at home,people often order or cook       food. But they can’t eat it up. When they go out of a restaurant, full and happy, they never look back       the uneaten food on the table again.Should Chinese consumers(消费者)feel       for the terrible waste?
In schools, we can often see a lot of students         food away after meals and they only eat the food they like.
Everyone is supposed to have enough food to eat. However, in some places, the food is so little        a lot of people died from hunger.Although China has tried hard to solve the        of hunger over the past thirty years,the job is not finished yet.Food is important to us all.We   can’t live      food.So        is necessary for us to love food and try to eat up everything on our plates.When we eat in restaurants,we should pack up the leftovers(剩菜剩饭).we also need to tell other people to stop       food as soon as possible.
小题1:
A.200 millionB.200 millions C.200 million ofD.200millions
小题2:
A.too manyB.many tooC.too muchD.much too
小题3:
A.inB.atC.onD.up
小题4:
A.interestedB.excitedC.happyD.sorry
小题5:
A.throwB.threwC.thrownD.to throw
小题6:
A.whichB.whenC.whereD.that
小题7:
A.problemB.questionC.dangerD.mistake
小题8:
A.noB.withoutC.hasn’tD.haven’t
小题9:
A.itB.heC.sheD.they
小题10:
A.wasteB.to wasteC.wasting D.to be wasted
填空题