题目

Once there was a man who had lost one of his arms in an accident. Day by day he got more and more 41 , thinking of not being able to do lots of things 42 he used to do. One day he got so disappointed that he 43_ to kill himself. He found a tall building and  44  to the top of it. Standing on the edge of the building, he was looking down to have a  45  look at the world before  46 off. Then he caught sight of a man  47    along the sidewalk, whistling and kicking up his heels. When the man came 48   , he found that this man didn’t have any arms at all. He thought to himsel如图所示，光滑水平面右端B处连接一个竖直的半径为R=0.5m的光滑半圆轨道．在距离B为x的A点，用水平恒定推力F=20N将质量为m=2kg的小球从静止开始推到B处后撤去水平推力，质点沿半圆轨道运动到最高点C处后又正好落回A点．则：（1）小球到底C点时对轨道的压力为多少？（2）距离x的值应为多少？（ g=10m/s2）