题干

一定质量的理想气体被活塞封闭在汽缸内,如图所示水平放置 . 活塞的质量 m=20kg ,横截面积 S=100cm2 ,活塞可沿汽缸壁无摩擦滑动但不漏气,开始使汽缸水平放置,活塞与汽缸底的距离 L1=12cm ,离汽缸口的距离 L2=4cm. 外界气温为 27℃ ,大气压强为 1.0×105Pa ,将汽缸缓慢地转到开口向上的竖直位置,待稳定后对缸内气体逐渐加热,使活塞上表面刚好与汽缸口相平,已知 g=10m/s2 ,求:
①此时气体的温度为多少;
②在对缸内气体加热的过程中,气体膨胀对外做功,同时吸收 Q=390J 的热量,则气体增加的内能 △U 多大.
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解: ① 当气缸水平放置时, p0=1.0×105P

同类题2

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月亮上的家

    随着现代科学的不断发展,月球已经变成人类的第二故乡,我在月球上拥有了一个全新的家,我把房子建成蘑菇形,外面涂上乳白色的高科技涂料。从蘑菇根部的大门进去,顺着螺旋形的楼梯来到楼上,楼上是我的卧室,打开窗户,就可以望见院子中绿草地上的小兔。这些小兔是嫦娥姐姐送来的,嫦娥姐姐是养兔专家,她很喜欢我,就送了我几只小兔子。现在,这些小家伙正竖着长长的耳朵,三瓣嘴一动一动的,可爱极了。

    我还在院子里栽了许多树木,别看这些树木长得高大、粗壮,它们可是我上个月才栽的,因为运用了最新的科学技术,所以它们能在短时间内快速成长,不仅我家,家家户户和大街上都有郁郁葱葱的大树。这些树不断提供着氧气,从而解决了人们的呼吸问题。

    在月球上生活,会有许多全新的感觉。比如:我有独特的运动方式,上学的时候,我就蹦蹦跳跳地去学校,月球上的引力是地球上的六分之一,轻轻一跳,就可以跳三米多高,跳到空中,有一种飞翔的感觉,许多小朋友也跟我一样跳着去上学,这成了月球上的一大景观。

    放假时,我参加了学校举办的夏令营,同学们在老师的带领下乘坐星际列车去宇宙各地旅游。别愁我们和其他星球的小朋友无法交流,宇宙通用语就是汉语,我们可有得天独厚的优势。

    如果我想家了,就坐着自家的星舰回到祖国。就这样,我有时生活在月球上,有时生活在地球上。浩瀚的宇宙任我遨游,这才是真正美妙的生活。

同类题5

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    We want our children to succeed, in school and, perhaps even more importantly, in life. But the paradox(悖论) is that our children can only truly succeed if they first learn how to fail. Consider the finding that world-class figure skaters fall over more often in practice than low-level figure skaters. At first sight this seems contradictory. Why are the really good skaters falling over the most?

    The reason is actually quite simple. Top skaters are constantly challenging themselves in practice, attempting jumps that stretch their limitations. This is why they fall over so often, but it is precisely why they learn so fast. Lower-level skaters have a quite different approach. They are always attempting jumps they can already do very easily, remaining within their comfort zone. This is why they don't fall over. In a superficial sense, they look successful, because they are always on their feet. The truth, however, is that by never failing, they never progress.

    What is true of skating is also true of life. James Dyson worked through 5,126 failed prototypes(原型) for his dual cyclone vacuum before coining up with the design that made his fortune. These failures were essential to the pathway of learning. As Dyson put it: “You can't develop new technology unless you test new ideas and learn when things go wrong. Failure is essential to invention.”

    In healthcare, however, things are very different. Clinicians don't like to admit to failure, partly because they have healthy egos(自我)(particularly the senior doctors) and partly because they fear litigation(诉讼). The consequence is that instead of learning from failure, healthcare often covers up failure. The direct consequence is that the same mistakes are repeated. According to the Journal of Patient Safety, 400,000 people die every year in American hospitals alone due to preventable error. Until healthcare learns to respond positively to failure, things will not improve.

    But let us return to children. One of the major mistakes in education in the 1970s was the attempt to equip children with confidence by giving them lots of successes (setting the bar very low). The consequence was that the ego of kids became bound up with success, and they became unable to take risks and collapsed as soon as they hit a proper challenge.

    We need to flip(翻转) this approach. In a complex world, failure is inevitable. It is those individuals and institutions that have the flexibility to face up to failure, learn the lessons and adapt which eventually excel(突出).