题目

瀑布从10m高处以2m/s的初速度竖直落下，如果它减少的机械能的20%用来使水的温度升高，水升高的温度是多少？水的比热容为4.2×103J/（kg・°C）. 答案：5×10-3℃【试题分析】 I ________this book for about a month, so I have to return it as soon as possible.A. have borrowed B. have keptC. have bought D. have posted