如图所示，一个壁厚可以不计、质量为M的气缸放在光滑的水平面上

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问题计算题

如图所示，一个壁厚可以不计、质量为M的气缸放在光滑的水平面上，活塞的质量为m，面积为S，内部封有一定质量的气体．活塞不漏气，摩擦不计，外界大气压强为P₀，若在活塞上加一水平向左的恒力F( 不考虑气体温度的变化) ，求气缸和活塞以共同加速度运动时，气缸内气体的压强多大？

答案

解：设稳定时气体和活塞共同以加速度a向左做匀加速运动，

这时气缸内气体的压强为p，

分析它们的受力情况，分别列出它们的运动方程为：

气缸：pS-P₀S =Ma ①

活塞：F+P₀S-pS=ma ②

将①②相加，可得系统加速度

将其代入①式，

化简即得气缸内气体的压强为

完形填空

It’s a sad and familiar sentence from a beggar that we often hear. Usually, when asked “Can you spare some   36  ?” I’ve been struck with a feeling of   37  if I passed by without giving a coin or two.
My conscience was hurt again when I was making a   38  in Venice in 2006. I was sitting in a quiet café. Outside the café on the street was an old woman on her knees,    39 . Steady streams of   40  were walking past her. A young backpacker stood away from the crowd drinking something, but I noticed he was also    41   the woman.
She knelt motionlessly, her head almost touching the ground, a worn blanket providing little    protection   42   the cold. The sight was especially   43  when compared with the signs of the   44  city around her.
A tourist group hurried along the street,   45  at the woman and walked on. Another group of tourists arrived,   46  again, walked past her. The backpacker watched. Then, as I prepared to leave, I stopped at the sight of the backpacker   47  and placing some money in the woman’s cup. He did this rather   48 , just before the arrival of another tourist group. I watched   49  the leader of the group stopped and put some money in the cup. With the young man   50  the way, other tourists followed.
The young backpacker   51  this process in front of the next tour party going past. Once again, the subtle peer(同伴) pressure   52  on the tourists, who all added coins to the cup. His work   53 , the young man walked over to the old beggar woman and said, “I hope that helps a bit.”
I placed some money in the woman’s cup and 54  my tour, light-hearted after witnessing such a   55  act of caring.

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单项选择题

“杀出一条血路”、“时间就是生命”、“实干兴邦”、“三天一层楼”……30年来，无数口号从深圳叫响全国，这些热词快语铭记着这片土地上那些惊心动魄、荡气回肠的历史事件，见证了一代人打拼、奋斗、奉献的燃情岁月，体现了深圳精神是探索者的精神遗产。深圳精神是（）

①中 * * 精神的具体体现

②中 * * 在革命时期的精神体现

③团结统一、爱好和平的体现

④勤劳勇敢、自强不息的体现

A.①④

B.③④

C.①②

D.②③

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