问题 计算题

(选修3-3选做题)

如图所示,一个上下都与大气相通的直圆筒,内部横截面积为S=0.01m2,中间用两个活塞A和B封住一定质量的气体。A、B都可沿圆筒无摩擦地上下滑动,且不漏气。A的质量不计,B的质量为M,并与一劲度系数为k=5×103 N/m的较长的弹簧相连。已知大气压p0=1×105 Pa,平衡时两活塞之间的距离l0=0.6 m,现用力压A,使之缓慢向下移动一段距离后,保持平衡。此时用于压A的力F=500 N。求活塞A下移的距离。

答案

解:设活塞A下移距离为l,活塞B下移的距离为x

对圆柱筒中的气体运用玻-马定律,可得方程:

活塞B移动x后弹簧的弹力有F=kx

将这两个方程联立,去掉x得

将数值代入得l=0.3 m

阅读理解

Some British and American people like to invite friends for a meal at home. You should not be upset(不安的)if your English friends don’t invite you home. It doesn’t mean they don’t like you. Dinner parties usually start between 7 and 8 p.m. and end at about 11. Ask your hosts(主人)what time you should arrive. It’s polite to bring flowers, chocolates or a bottle of wine as a gift. Usually the evening starts with drinks and snacks(小吃). If you want to be extra polite, say how much you like the room, or the pictures on the wall. But remember-it’s not polite to ask how much things cost. In many families, the husband sits at one of the table and the wife sits at the other end. They eat with their guests. You’ll probably start the meal with soup or something small, then you’ll have meat or fish with vegetables, and then dessert(甜点心), followed by coffee. It’s polite to finish everything on your plate and to take more if you want it. Did you enjoy the evening? Call your hosts the next day, or write them a short “thank you” letter. British and American people like to say “thank you, thank, thank you” all the time!

小题1:If your English friend doesn’t invite you to dinner at home, it means he or she ______.

A.doesn’t like you

B.likes you

C.can’t afford to do so

D.is too busy小题2:It’s impolite ______.

A.to ask about the price of a certain thing

B.to say “thank you” to hosts

C.take nothing with you when you are invited to dinner

D.to eat up everything on your plate小题3:The meal ends with _______ usually.

A.soup

B.coffee

C.meat or fish

D.dessert小题4:When you are invited to a dinner party, you’d better _______.

A.ask what time you should arrive

B.take your wife with you

C.drink as more as possible

D.eat more snacks as you can小题5:Which of the following is true?

A.The hosts like the people who sit closer to them.

B.The hosts like the people who ask them time, price, age, etc.

C.The husband and the wife usually sit together.

D.You can call your host the next day or write a letter of thanks after that

名词解释