问题 选择题

将一物体以某一速度从地面竖直向上抛出,设物体在运动过程中不受空气阻力,则物体

A.刚抛出时的加速度最大

B.在最高点的加速度为零

C.上升时间大于下降时间

D.上升和下降过程中重力做的总功等于零

答案

答案:D

题目分析:如果物体受到的阻力为零,则物体只受重力作用,由牛顿第二定律可得,它的加速度是不变的,A不对;由于物体处于最高点时,也受到重力的作用,故最高点时的加速度仍为g,故B也不对;上升与下降的加速度大小相等,路程相等,上升的初速度为0,下降的初速度也为0,故下降是上升的逆过程,二者的时间是相等的,故C也不对;由于上升时重力对物体做负功,下降时重力对物体做正功,二个功还相等,故总功等于零,D是正确的。

单项选择题 案例分析题
阅读理解

Chinese tennis player Li Na didn’t win the Australian Open Championship on Saturday, but she still made the history books.

Li, who lost to Kim Clijsters of Belgium in three sets (3-6, 6-3, 6-3), is the first player from China to make it to a Grand Slam final.

The boss defeated a bit of the feel-good story for China and for Li, who on Thursday defeated No. 1 player Caroline Wozniacki in the semifinals in Melbourne. Li is ranked fifth.

In an interview Li said she was proud of her effort. “I think I play great tennis,” she said. “ I mean, she plays better than me. After the match, I make a joke: tennis should only play one set.

Bai Yan, a member of China’s men’s national team member and Li Na’s friend, said the loss was disappointing, but still a bright starting point.

“To tell you the truth I feel a little bit down, all of us. But you know she is still the best, and she’s still our hero in everybody’s eyes,” said Bai. “This is just the start.”.

Win or lose, Li’s appearance in the Australian Open finals was seen as a major victory for tennis in China, where badminton and table tennis rules.

Fans across China gathered to watch the match. Li’s mother joined fans at a restaurant in her hometown of Wuhan. In Bejing, fans crowded together to watch China’s national tennis match.

“ Tennis is still relatively a new sport in China,” said Michael Chang, the Chinese-American who was the first Asian grand slam champion, in an interview with CNN. “ To be able to see Li Na have as much success as she has… this could be the start of something very special for tennis in China.”

“Li will definitely change the sport of tennis in China and that is a great thing,” Chang said.

小题1: What’s the main idea of the passage?

A.Chinese tennis star Li Na’s tennis career.

B.A fierce tennis match at Australian Open.

C.Chinese tennis star made history at Australian Open.

D.Chinese tennis remained to be tested and challenged.小题2: Which is true according to the passage?

A.Li Na’s failure let the Chinese down.

B.Li Na ranked fifth at Australian Open.

C.LI Na’s mother attended the match with her.

D.Li Na made a new starting point of China小题3:What’s the meaning of the underlined words “tennis should only play one set” (Para 4)?

A.Li Na was not satisfied with the rule of tennis match.

B.Li Na was not satisfied with her own performance.

C.Li Na had a bad opinion of Clijsters.

D.Li Na took pride in her effort.小题4:According to what Chang said in the last two paragraphs, we can imply that ________.

A.it’s normal that Li Na failed because tennis is a new sport in China

B.Li Na has the advantage to change tennis sport in China

C.China still falls behind other countries in tennis sport

D.Li Na has great difficulty in defeating others because of weak ability