题干

用如图所示的实验装置测量杠杆的机械效率.实验时,竖直向上匀速拉动弹簧测力计,使挂在较长杠杆下面钩码缓缓上升.实验中,将杠杆拉至图中虚线位置测力计的示数F=____ N,钩码总重G为1.0N,钩码上升高度h为0.1m,测力计移动距离s为0.3m,则杠杆的机械效率为____  %.请写出使用该杠杆做额外功的一个原因:____ .

上一题 下一题 0.0难度 选择题 更新时间:2019-06-13 01:10:16

答案(点此获取答案解析)

0.5,66.7,由于使用杠杆时需要克服杠杆自重(克服摩擦力)等做功

同类题5

短文填空。用下面方框中单词的适当形式填入短文空格内,使短文 意思正确、通顺。

back bad        express         feel     it     loud  luck     simple     sweet      thank      two    warm

Once upon a time, a young man came across a spring(泉水) of clear water while crossing the desert. The water was very sweet, and he filled his leather container(皮革容器) so that he could bring some____ to his teacher. After a four-day journey, he presented the water to his teacher.

The old man took a deep drink, smiled____ and thanked his

student very much for the sweet water. The young man returned to his village with a happy heart. After a while, the teacher let a____ student taste the water. He spat (吐) it out, saying it was terrible. It was clear that the water had become no longer fresh sweet because of the old leather container. The student questioned his teacher, “Master, the water tasted strange. Why did you still like it?” The teacher replied, “You____ tasted the water while I tasted the gift. The water was the container for an act of love and kindness and nothing could be ____ .”

After reading the story, we can understand that when we receive a chocolate as a gift from a child, we get more than the chocolate

____ . What we should do properly is to express ____ naturally to him or her because we love the idea within the gift.

Gratitude (感谢) doesn’t always come  naturally.____ , most children and many grown-ups like only the thing given rather than the ____ shown in it. We should remind ourselves and teach our children about the beauty of feelings and____ of gratitude. After all, gifts from the heart are really gifts of the heart.