问题 填空题

一辆汽车在恒定的功率牵引下,在平直公路上由静止出发,经4min的时间行驶1.8km,则在4min末汽车的速度(   )

A.等于7.5m/s

B.大于7.5m/s

C.等于15m/s

D.15m/s

答案

BD

 汽车在恒定功率下由静止启动是加速度越来越小的变加速运动,很难通过运动方程求瞬时速度,一般的方法是由动能定理求出动能、再求速度但这必须要知道牵引力、阻力所做的功。而现在这些条件都未知,但在恒定功率下,其4min内的平均速度,由于加速度变小,所以末速度,同时由于位移关系,其图象如图,为一上凸的曲线。打斜线部分“面积”相等,即位移为,如果,则位移;而则位移,故,正确选项是BD。 

写作题

任务型阅读。

     Tina, Mike, Jeff, Linda和Vera在生活、学习和运动中遇到一些问题,请阅读下面五个片段(1-5),并从后面的选项(A-E)中帮他们找到解决问题的方法或建议。

(     )1. Tina has been invited to one of her friends’ birthday party next Sunday. She is worried about this

now because she has never taken part in any birthday party, and nobody can tell her something about it.

(     )2. Mike’s favorite is playing sports. He gets up early at 6:00 every morning. Then he goes out to

exercise by the riverside. He runs along the river for nearly half an hour, and then takes a walk for a few

minutes. He goes back home for breakfast at 7:30. But he always feels weak after morning exercises.

(     )3. Jeff is interested in the computer. His parents bought him a Dell computer last month. He wants to

surf the Internet. But he heard that there are many terrible things for kids on the Internet. His parents don’t have the knowledge about this.

(     )4. Linda’s parents will be away for China on business for more than half a year very soon. She can’t

go with them because she has to go to school. She will be at home alone. Nobody will take care of her,

and she can’t do chores herself.

( )5. Vera is a clever girl. She does well in her studies.But Vera doesn’t like playing with her classmates, and she feels bored when her classmates ask her questions about studies. So she can’t get along well with her classmates.

A   Don’t give your personal information such as your address, telephone number, etc. on the Internet without your parents’ permission. Never agree to get together with someone you “meet” online and never send a person your picture or anything else without first checking with your parents.

B   On the day of the party, make sure you arrive on time and show that you’re happy to be there. Wear

something suitable. Greet your friend with a “Happy Birthday” and hand over the gift. Make sure you have put a card with your name on it.

C   Always smile, so people don’t think you are serious and hard to get along with. Be polite and modest. If you are rude, people will not like you. If people have troubles, you help them. Then, when you have

troubles, they will help you, too.

D   Parents should get the kids to do their chores around the house. If their clothes need washing, they wash them themselves. Let the kids prepare their own meals. Let them clean their room, cook for themselves, wash the dishes, etc.

E   Let’s say that the last time you eat something at night is at 6 or 7 pm (just an example). The following

day, you don’t eat breakfast but wait until you finish sports - you’ve gone many hours with nothing in your stomach. Your body has to work hard.It’s not good.What’s more, consider reducing the time and strength of your morning exercises.

单项选择题