One night a man came to my house. He told me, 41 is a family with eight children.They have not eaten for days. After I asked him where the family was, I took some food 42 me and left. When I finally got to that family, I 43 those little children were too hungry to say a 44 . There was no sadness in their eyes, just the deep pain of hunger. I gave the food to the mother. She took half of it, and then 45 . When she returned, I asked her, 46 did you go? She gave me this simple 47 , “To my neighbors --- they are also 48 !” I was no一滑块在水平地面上沿直线滑行,t=0时其速度为2.0m/s。从此刻开始在滑块运动方向上再施加一水平拉力F,力F和滑块的速度v随时间t的变化规律分别如图7甲和乙所示。设在第1s内、第2s内、第3s内力F对滑块做功的平均功率分别为P1、P2、P3,则( )
A.P1>P2>P3
B.P1<P2<P3
C.0~2s内力F对滑块做功为4J
D.0~2s内摩擦力对滑块做功为4J