题目

张明同学做“用单摆测重力加速度”的实验， (1)测摆长时，若正确测出悬线长l和摆球直径d,则摆长为             (2)测周期时，当摆球经过平衡位置时开始计时并计数为1次，测出经过该位置N次的时间为t,则周期为               （3）他实验测得的g值偏小，可能的原因是              A.测摆线长时摆线拉得过紧 B.摆线上端未牢固地系于悬点，振动中出现了松动，使摆线长度增加了 C.开始计时时，秒表提前按下 D.实验中误将49次全振动As a student, I was most afraid to answer questions in class, and I found that the students around were just like me. At the beginning of each class, when the teacher asked a question, I always lowered my head because I was afraid that the teacher saw me. One day, in a foreign language class, Mr. Black gave us a lesson. He wanted us to be active in class, so he asked us some questions, but no one answered. "Let me tell you a story first," he said."When I came to the United States to study, the university often invited famous people to make speeches. Before the beginning of every speech, I found an interesting thing. The students around me always took a cardboard folded(折叠的) in half, wrote their names in bold(黑体) with the most eye-catching(引人注目的) color, and then placed the cardboard on the seat. So when the speaker needed the answers from the students, he could see it and call a listener's name directly.""I couldn't understand that. My classmate told me the speakers were all top people, who meant chances. When your answer was to his surprise, it meant he might give you more chances. In fact, I really saw a few students got great chances because of that."After listening to the story, I understood that the chance will not find you itself. You must show yourself all the time so that you can find a chance on the card. 根据上面短文的内容回答问题(每题不超过9个单词)1.Why did the writer lower his head?_________________________________________________2.What did Mr. Black want the students to do in his class?_________________________________________________3.How did the speaker get to know the students' names?_________________________________________________4.When might the speaker give you more chances according to the passage?_________________________________________________5.How can you find a chance on the card?__________________________________________________