“探究动能定理”的实验装置如下图所示，当小车在两条橡皮筋作用下弹出时，橡皮筋对小车做的功记为W0。当用2条、3条、4条……完全相同的橡皮筋并在一起进行第2次、第3次、第4次……实验时，橡皮筋对小车做的功记为2W0、3W0、4W0……，每次实验中由静止弹出的小车获得的最大速度可由打点计时器所打的纸带测出。关于该实验，下列说法正确的是 （ ）
A．某同学在一次实验中，得到一条记录纸带，纸带上打出的点，两端密、中间疏，出现这种情况的原因，可能是木板倾角过大
B．当小车速度达到最大时，小车在两个铁钉的连线处
C．应选择纸带上点距均匀的一段计算小车的最大速度
D．应选择纸带上第一点到最后一点的一段计算小车的最大速度
答案：C
木板倾角过大时，相邻两点之间的间隔会越来越大，选项A错误；当橡皮筋处于原长时，小车达到最大速度，而不是小车在两铁钉的连线处，选项B错误；本实验平衡阻力后，橡皮筋做功结束后，小车做匀速直线运动，选项C正确、选项D错误。
Once there lived a farmer called Henry. He had a brother, Mike, in town who was an excellent gardener. His skilland his beautiful trees were everywhere. One day, Henry went to town to visit Mike. "Look, my brother," said Mike, "Here is the best tree from mygarden. Take it home and it so that you, and your children, and your children's children can enjoy it.” Henry was with the apple tree and went back home. The next morning, he began to where he should plant it. "If I plant it on the hill,” said he to himself, "the wind might catch it and flown the fruit; If I plant it closeto the road, people who pass by will pick some of them; But if I plant it ..." he planted the tree in the comer behind his house, where no one else could notice it. But the tree bore(结出)no fruit the first year, nor the second. Then Henry sent for his brother and said to him , “You have cheatedme. This is the third year and it bring me but leaves. When Mike saw where the tree was planted, he laughed and said, "You have planted the tree in such a cold cornerwithout or warmth. How, then, could you expect flowers and fruil?"
|