题目

画出图中所示A点F1的力臂与绳子在B点拉力F2的力臂(O点为支点)。 答案:【答案】【解析】延长作用在A点力的作用线,过O点作力的作用线的垂线,该垂线段即为的力臂;由图可知,杠杆在水平位置静止,作用在杠杆上的B点对杠杆施加力的方向竖直向下,此时力的作用线垂直于杠杆,则的力臂在杠杆上。所求力臂画图如下所示Little Mike’s grandmother died weeks ago. He missed her very much. One afternoon Mike went to the city park where his grandmother used to go. There he saw an old lady. She looked very kind. She was sitting there, watching pigeons(鸽子). Little Mike went up and sat next to her. He took out his food and drinks and gave some to her. She smiled at him. Her smile was very sweet and Mike wanted to see it again. She seemed to understand him, so once again she smiled. Mike was very happy. They sat there all the afternoon, eating and talking. As it was dark, Mike got up to leave. Before he left, he hugged the old lady and she gave him her sweetest smile.When Mike got home, his mother was surprised by the happy look on his face. “ I met an old lady in the park. Her smile was like the smile I used to see on Grandmother’s face.”The old lady also returned to her home happily. She told her son she had food and drinks with a little boy. “ He was as lovely as Bill.” She said. Her son was surprised, because he had never been so happy since Bill, her grandson, died weeks ago.1.Little Mike went to the park and ________.A. played with pigeons B. fed pigeons C. met an old lady D. saw a friend of his grandmother’s 2.The old lady’s smile showed ________.A. she hated to meet the boy B. she wanted to get some drinksC. she missed her son D. she liked the little boy3.Mike felt very happy because ________.A. he gave the old lady some food and drinks B. the old lady’s smile was like his grandmother’s smileC. he met his grandmother in the city park D. he saw many lovely pigeons in the park4.Mike and the old lady ________.A. were good to each other(相互) B. knew each other well C. often met in the park D. did nothing that afternoon5.What do we learn from the story?A. When one feels unhappy, he must go to a park.B. Old people are always kind and happyC. Children should be polite to old people .D. When people get on well, they feel happy.  
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