问题
填空题
用动滑轮把重400N的物体匀速提高10m，拉力所做的功为5000J，如图所示，有用功是 ______J，动滑轮的机械效率是 ______．
答案
由题意知，h=10m，
W有=Gh=400N×10m=4000J，
W总=5000J，
η=
×100%=W有 W总
×100%=80%．4000J 5000J
故答案为：4000，80%．
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用动滑轮把重400N的物体匀速提高10m，拉力所做的功为5000J，如图所示，有用功是 ______J，动滑轮的机械效率是 ______．
由题意知，h=10m，
W有=Gh=400N×10m=4000J，
W总=5000J，
η=
×100%=W有 W总
×100%=80%．4000J 5000J
故答案为：4000，80%．
| 仔细阅读下面的短文，用方框内所给的词选择填空，使短文表达正确、意义通顺。 | |
course, I do." But maybe you don't. It is true that all parents can remember clearly when 2_____ their children's birthdays. However it is a pity that few children know exactly when their parents birthdays are. Most parents can easily 3_____ the food their children favor. The other way round, some students don't know 4_____ their parents like most of all. Sometimes we can hear parents 5_____ that their children don't talk with them as often as 6_____. Children are growing and the generation gap (代沟) are widening. If you love your parents well, let them 7_____ your love. Give them a birthday gift on their 8_____ day, help them do some housework as often as possible, bear in mind what your parents like or don't like. Don't always say things 9_____ your parents. Talk with them more often and 10_____ them more. |