题干

百米赛跑时,如果终点的计时员不是看到发令枪冒白烟开始记时,而是等听到发令枪的枪声开始计时,他计得的某运动员百米成绩是12.5秒,这个成绩准确吗?是提高了他的成绩还是降低了他的成绩?较准确的成绩为多少?请结合物理知识,并通过计算回答.(若声音在空气的传播速度是340m/s)

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解:(1)不准确;因为百米赛跑场上记时裁判从看到发令枪冒白烟开始记时,而不是听到枪声时计时.如果听到枪声才计时,因为光速比声速大,声音传播需要时间多,这样少计了些时间,听到枪声才开始计时,说明枪声已经传播100米到达终点时才开始计时,测得时间肯定少了,少的时间为t=sv=

同类题2

阅读下列内容, 从每小题所给的 A、B、C、D 四个选项中选择一个最佳答案。

Who is the greatest teacher in Chinese history? Many people would think of Confucius(孔子), whose birthday was September 28. Although he lived over 2, 000 years ago, people still remember and respect him for his contribution(贡献) to the education today.

Confucius lived in the Kingdom of Lu, which lies in Shandong Province. He lived during the Spring and Autumn Period. He had a hard childhood. His father died when he was only 3. His mother brought him up. As a child, he had to work to help his mother, but young Confucius didn't give up studying. He visited many famous teachers and learned music, history, poetry and sports.

Later, he became a teacher and started the first public school in Chinese history. At that time only children from noble families could go to school, but Confucius believed everyone should go to school if they wanted to learn. He had about 3, 000 students in his lifetime.

Today, people still follow Confucius' lessons. He told us that we all have something worthy to be learned. “When I am with three people, one of them must be better than me in some areas. I choose their good qualities and follow them.”

He also taught us that thinking is very important in study. “All study but no thinking makes people puzzled (困惑的). All thinking but no study makes people lazy.” Confucius is not only a great teacher, but also a famous thinker with wise thoughts about the world and society. His most important teachings are about kindness and good manners. “A person should be strict with himself, but be kind to others.” he said.