问题 问答题

如图所示,半径为R的四分之一圆弧支架,支架底ab离地面距离4R,圆弧边缘C处有一个小定滑轮,一轻绳两端分别系着质量为mm2的物体(可视为质点),挂在定滑轮两边,且m1大于m2,开始时两物体均静止。(不计一切摩擦)

求:(1)m1经过最低点a时的加速度。

(2)若m1经过最低点时绳断开,m1落地点离a的水平距离为多少?

(3)为使 m1能到达a点m1与m2之间必须满足什么关系?

答案

(1)(2)(3)

(1)如图将m1的运动分解,,m1 m2组成的系统机械能守恒,

解得:

(2)绳断后m1做平抛运动,平抛时间

(3)由 可知当可到达a点。

阅读理解

All of the people have ambitions. An ambition is something we want to do, want to have, or want to be. A student’s ambition, for example, might be to pass his or her exams. An athlete’s ambition could be to win an important competition. A businessman’s ambition is usually to make a lot of money.

Not all ambitions are about success at work, however. Some people just want to be good people, have a happy family or help others.

Ben’s ambition is to be a sports writer. He writes the sports reports for his class newspaper. He likes most sports, but swimming and football are his favorites.

Trudy’s ambition is to be a concert pianist. She is very serious about it and practices every day with her best friend Lily. It is very important to her.

Harry’s ambition changes every day! One day he wants to be an astronaut. The next day he wants to be a pop singer. Then he wants to drive a racing car. His mother would be happy if his ambition was to get up in time for school every day!

What is your ambition?

小题1:The Chinese meaning of the underlined word “ambition” is “_______”.

A.信心

B.希望

C.理想

D.幻想小题2:What does a businessman want?

A.To pass the exams.

B.To win a competition.

C.To make a lot of money.

D.To get a good job.小题3:What does Ben want to be?

A.A newspaper reporter.

B.A famous swimmer.

C.A great football player.

D.A sports writer.小题4:Why does Trudy practice the piano every day?

A.Because she wants to be a concert pianist.

B.Because she wants to help Lily.

C.Because she wants to be a pop singer.

D.Because her mom tells her to.

判断题