如图所示，水平面内有三块相同的圆板，分别用两根、三根、四根不可伸长的细线按三种不同的方式拴结一个质量为m的小球，细线的另一端都栓结在圆板边缘，且栓结点均匀分布在圆周上，三种情况细线与竖直方向的 夹角分别为30°、45°、60°，三种情况绳子的拉力分别为F1、F2、F3它们的大小关系是（ ）
A．F1＞F2＞F3
B．F1＜F2＜F3
C．F1＞F3＞F2
D．F2＞F1＞F3
三幅图中，小球均受重力和绳子的拉力，根据平衡条件，拉力的竖直分力的合力等于重力，故有：
2F1cos30°=mg ①
3F2cos45°=mg ②
4F3cos60°=mg ③
解得：F1=
mg3 3
F2=
mg2 3
F3=
mg1 2
故F1＞F3＞F2；
故选C．
I was 14 when Mr. Ingram hired me as a farmhand. It was the first time I was actually for work. One day Mr. Ingram found an old truck that was in the soft,sandy soil of our field. It was full of melons that someone had tried to from our farm before his truck got caught in the mud. Mr. Ingram explained that the truck’s owner would be soon, and he wanted me to watch and learn. It wasn’t long a local guy with a terrible reputation for fighting and stealing showed up with his two fully-grown sons. They looked really . Calmly Mr. Ingram said, “Well, I see you want to some watermelons from us.” There was a long before the man answered, “Yeah, I guess so. What are you for them?” “Twenty-five cents each.” “Well, I suppose that would be enough if you help me get my truck out of here,” the man said. It turned out to be our biggest sale of the summer, and an awful, perhaps violent incident had been . After they left, Mr. Ingram smiled and said to me, “Son, if you don’t forgive your , you’re going to run out of friends.”
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