题目

用如图所示的滑轮组匀速提起重300 N的箱子,绳自由端5s内移 动2 m.滑轮组的机械效率为75%，则箱子上升高度为_______m, 拉力F的大小为______N,拉力F做功的功率为_______W. 答案：【答案】1 200 80 【解析】解答：由图可知n＝2（1）绳子自由端移动的距离是：2米，箱子上升的高度是：＝1m；（2）滑轮组的做的有用功是：W有用＝Gh＝300N×1米＝300J，所以滑轮组的总功是：W总＝＝400J，拉力F的大小是：F＝＝200N；（3）拉力F做功的功率为：P＝＝80W．请根据图片中的信息写一篇英语短文来介绍Mary一天的活动内容,60词左右。起床吃早饭去上学上课放学睡觉____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Mary has a healthy life. Every morning, she gets up at 5:30.She takes a walk. And then she eats breakfast at half past six. She walks to school at half past seven. School begins at eight o’clock. Mary...