问题
计算题
如下图所示，使用滑轮组拖动放在水平地面上的物体A在10s内匀速前进5m，若物体重为104N，物体与地面间的摩擦力为200N，滑轮组的机械效率为80%，机械自身摩檫不计，问：
（1）拉力做了多少功？额外功是多少？
（2）拉力F多大？
（3）拉力功率多大？（g=10N/kg）
答案
（1）1250J；250J
（2）125N
（3）125W
搜题请搜索小程序“爱下问搜题”
如下图所示，使用滑轮组拖动放在水平地面上的物体A在10s内匀速前进5m，若物体重为104N，物体与地面间的摩擦力为200N，滑轮组的机械效率为80%，机械自身摩檫不计，问：
（1）拉力做了多少功？额外功是多少？
（2）拉力F多大？
（3）拉力功率多大？（g=10N/kg）
（1）1250J；250J
（2）125N
（3）125W
One afternoon, I went to pick up my mother from work.I got there a little early, so I _______ (41) my car by a small park, and _______ (42) for her. As I looked outside the car window, I saw a little boy, around two years old, running _______ (43) on the grass as his mother _______ (44) from a short distance. The boy had a big smile on his face as if he had just been ______ (45) free from some sort of prison .The boy would then fall to the grass , (46) up , without looking back at his mother , run as_______ (47) as he could ,again , still with a smile on his face ,as if nothing had happened. At that moment, I thought to myself , “why aren’t most adults this way ?” Most adults, when they fall down, make a big deal out of it and don’t even _______ (48) a second attempt. They would be so _______ (49) that they would not try again if someone saw them fall .Or , because they fall , they would find a good _______ (50) for themselves that they’re not fit for it . They would end up too afraid to attempt again for fear of failure. However, with kids, when they fall down, they don’t consider their falling down as a failure, instead, they treat it as a _______ (51) experience. They try again and again until they _______ (52) .The answer must be that they have not connected“falling down” with the word “failure”. As a _______ (53), they are not discouraged in any way .Besides, they _______ (54) think to themselves that it’s quite okay to fall down and that it’s not wrong to do so. In other words ,they allow themselves to make _______ (55), so they remain energetic. I was deeply impressed by the boy’s persistence (坚持不懈) and the manner in which he did.
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