问题
计算题
用如图所示的滑轮组将重为4.2N的物体匀速提升0.1m，所用时间为5s，拉力F大小为2N，求：
（1）拉力的功率。
（2）滑轮组的机械效率。
答案
解：（1）s＝3h=3×0.1m＝0.3m，W总＝Fs＝2N×0.3m＝0.6J。
；
（2）W有＝Gh＝4.2N×0.1m＝0.42J，
。
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用如图所示的滑轮组将重为4.2N的物体匀速提升0.1m，所用时间为5s，拉力F大小为2N，求：
（1）拉力的功率。
（2）滑轮组的机械效率。
解：（1）s＝3h=3×0.1m＝0.3m，W总＝Fs＝2N×0.3m＝0.6J。；
（2）W有＝Gh＝4.2N×0.1m＝0.42J，。
根据对话内容，从对话后所给的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。（共5小题；每小题2分，满分10分）请把答案填在下面的方框内，否则不计分。） ---It’s so hard for me to learn English.Why is it so easy for you? ---I didn’t know you were having problems._1___But also, I really work at it. ---Well,I always do my homework and go to classes._2___ ---Well, you might try reading newspapers. And you can talk with Americans when you get a chance. ---__3_____ ---How about sitting next to an Amercian at lunch, or have you ever thought of asking someone over to your house for dinner? ---__4___But I’m a little shy to speak English. ---You won’t learn if you don’t try and speak.__5__They will give us a lot of help.
F. If I were you, I’d talk to the English teachers. G. Maybe it's easier for me because I already speak two languages.
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