题目

如图，两个大小相同小球用同样长的细线悬挂在同一高度，静止时两个小球恰好接触，两个小球质量分别为和 （），现将拉离平衡位置，从高处由静止释放，和碰撞后被弹回，上升高度为，试求碰后能上升的高度。（已知重力加速度为g）         物理答案 答案：碰前              得 碰撞过程动量守恒        碰后反弹上升       上升       联立解得                Many teenagers（青少年） feel that the most important people in their lives are their friends. They believe that their family members don’t know them as well as their friends do. In large families, it’s quite often for brothers and sisters to fight with each other and then they can only go to their friends for some ideas.It is very important for teenagers to have one good friend or a group of friends. Even when they are not with their friends, they usually spend a lot of time talking among them on the phone. The talk between friends is very important in children’s growing up, because friends can discuss something. These things are difficult to say to their family members.However, parents often try to choose their children’s friends for them. Some parents even stop (阻止)their children from meeting their good friends. Do you think of the following questions?Who chooses your friends? Do you choose your friends or your friends choose you? Have you got a good friend your parents don’t like? Your answers are welcome.1. When teenagers have something difficult to say to their parents, they usually _______A. stay alone at homeB. fight with their parentsC. discuss it with their friendsD. go to their brothers and sisters for help2. The sentence “Your answers are welcome.” means“ ____ ”.A. You are welcome to discuss the questions with us.B. We’ve got no idea, so your answers are welcome.C. Your answers are always right.D. You can give us all the right answers.3. Which of the following is the writer’s attitude（态度）?A. Parents should choose friends for their children.B. Children should choose everything they like.C. Parents should understand their children better.D. Teenagers should go to their friends for help.