问题
单项选择题
边长为a的正方形截面如图所示，则该截面对y1轴的惯性矩Iy1为（）。
A．A
B．B
C．C
D．D
答案
参考答案：C
解析：
过C点做形心轴yC与y1平行，则IyC+b2A，IyC+b2A
。
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边长为a的正方形截面如图所示，则该截面对y1轴的惯性矩Iy1为（）。
A．A
B．B
C．C
D．D
参考答案：C
解析：
过C点做形心轴yC与y1平行，则IyC+b2A，IyC+b2A。
We spent a day in the country and picked a lot of flowers. Our car was of flowers inside! the way home we had to stop at traffic lights, and there my wife saw the bookshelf. It stood outside a furniture（家具）shop. “Buy it,” she said at once. “We’ll carry it home on the roof-rack（车顶架）. I’ve always wanted like that.” What could I do? Ten minutes I was twenty dollars poorer, and the bookshelf was tied on to the roof-rack. It was tall and narrow, quite heavy . As it was darker, I drove slowly. Other drivers seemed more polite than usual that evening. The police even stopped traffic to let through. Carrying furniture was a good idea. After a time my wife said, “There a long line of cars behind. Why don’t they overtake（超车）?” Just at that time a police car did overtake. The two police officers looked at us seriously when they went past. then, with kind smile they asked us to follow their car through the busy . The police car stopped at our village church. One of the officers came to me. “Right, sir,” he said. “Do you need any more help now?” I didn’t quite understand. “Thanks, officer,” I said. “You’ve very kind. I live just down the road.” He was looking at our things: first at the flowers, at the bookshelf. “Well, well,” he said and laughed. “It’s a bookshelf you’ve got there! We thought it was else.” My wife began to laugh. Suddenly I understood the police drove here. I smiled at the officer. “Yes, it’s a bookshelf, but thanks again.” I drove home as fast as I could.”
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