题干

如图所示的情景中,关于力对物体做功的叙述,正确的是(  )

A: 大力士表演拉汽车前行,此时人拉车的力做了功

B: 起重机吊着重物水平移动,钢丝绳的拉力对重物做了功

C: 举重运动员举着杠铃不动,运动员对杠铃做了功

D: 足球在水平地面上运动,足球的重力对足球做了功

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A

同类题1

阅读理解

    You may think that light pollution isn't something extraordinarily important. You may believe that every other type of pollution has a larger impact on the environment that light pollution does. But light pollution is serious.

    Light pollution, or “sky glow”, is the glow you can see at night above cities and towns. Light pollution is a problem that has been accompanying man ever since he started his first fire some 15,000 years ago. Light pollution is the light that comes from streetlights, buildings, parking lots and any other source of light that is reflected or directed into the atmosphere.

    Urban light pollution means that one-fifth of the world's population can no longer see the Milky Way(银河) with the naked eye(肉眼). Many city kids, even if they did look through the orange smog above their heads, would probably see only a handful of stars. We have lost our view of the stars, and we have mucked up our  night-time environment as well. Astronomers are calling for the dark places on Earth to be preserved as national parks.

    Lots of people find the ever-brightening night annoying, and animals that are programmed to prefer the dark may avoid a brightened habitat. Sea turtles can get lost searching for a beach to lay eggs, and their hatchlings(孵化的幼仔)may confuse over-lit beachfront resorts(度假胜地) for the ocean horizon, wasting precious energy needed to find the sea and escape predators(食肉动物). Because their necks aren't yet long enough to see things far away, baby turtles rely on the mirror image of the moon to guide them to the sea, to begin their new life. A car may even hit a particular turtle, which was thinking the light from a nearby city was moonlight reflecting off the ocean waves. Birds that live in and around cities can die because of sky glow, too. The bright lights can blind them, leading to countless collisions with buildings and other tall structures.

    On an individual level, people can help reduce much sky glow by using lighting only when necessary. The stars above us are priceless heritage— for not only for astronomers but for all humans. More of our children should be able to look up at night and see the Milk Way.

同类题3

阅读《论毅力》一文,回答相关问题。
                                                                                                          论毅力
        ①普天之下古往今来种种成败的人和事,它们所经历的道路是如此的纷繁不同。推究他们为什么成功,又为什么失败,回答是有毅力的人就会成功,反之则是失败。
       ②人生的历程,大体逆境占了十分之六七,顺境也占了十分之三四,而顺逆这两种境遇又常常是相互交替着出现的。无论事情是大是小,必然会遇到几次乃至十几次的阻力,这种阻力虽然有大有小,但必定是不可避免的。那些意志和能力薄弱的人,开始的时候一定会说我想要如何如何,他心里认为天下事本来就是很简单容易的。等到马上尝试,阻力突然来临,就颓然丧失了信心。那些意志能力比较弱的人,凭着一时的意气,通过了第一关,遇到第二次挫折就退缩了;意志能力稍强的人,遇到三四次挫折才退缩;又坚强些的人,遇到五六次挫折才退缩。所做的事情越大,他遇到的挫折就越多,他不退缩的话也就越难。不是极其坚强的人,是很难达到成功的终点的。
       ③如果遇到挫折而不退缩,那么小的逆境之后,必定有小的顺境;大的逆境之后,必定会有大的顺境。经过了盘根错节的复杂情况以后,就会有迎刃而解的一天。旁观者只是羡慕别人的成功,认为这个人大概是个幸运儿,而老天特别宠爱他;又认为自己总是遭遇不顺利,所以成就也比不上他。这种人哪里知道所谓的“不顺”、“幸运”,他和我都是相同的,而是否能征服这些“不顺”,利用这些“幸运”,正是他成我败的区别所在。再拿驾船来做比方,如果用二十天的时间行走一千里的路程,其间风向潮流有时顺有时逆,常常交互错杂。他凭着艰苦忍耐的力量,迎着那逆风逆流冲了过去,然后能从容地前进,去渡过顺风顺水的一段。但是我或者一天就退回来了,或者两三天就回来了,或者五六天就回来了,因此也就始终不能到达彼岸了。
       ④孔子说:“譬如为山,未成一篑,止,吾止也;譬如平地,虽覆一篑,进,吾往也。”孟子说:“有为者,譬若掘并,掘井九仞而不及泉,犹为弃井也。”成败的规律,在此而已。