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例[2011年海南卷]一质量为1kg的质点静止于光滑水平面上,从t=0时起,第1s内受到2N的水平外力作用,第2s内受到同方向的1N的外力作用.下列判断中正确的是A.0～2s内外力的平均功率是9/4WB.第2s内外力所做的功是5/4JC.第2s末外力的瞬时功率最大
For example, a volume of 1kg of mass is stationary on a smooth water surface. From t = 0, 2N horizontal external force is applied in the first 1s and 1N external force in the same direction in the 2s. In the correct A.0 ~ 2s the average power of internal and external force is 9 / 4WB. The first 2s internal and external force work done is 5 / 4JC.