题干

在水平粗糙的地面上使一物体由静止开始作匀加速运动,如图所示,第一次是拉力,第二次是用推力,两种情况下力的作用线与水平方向夹角、力的大小、位移大小均相同,那么比较两种情况,则下列说法正确的是(   )

A:力F对物体所做的功相等

B:摩擦力对物体所做的功相等

C:物体的动能变化量相等

D:力F做功的平均功率相等

上一题 下一题 0.0难度 选择题 更新时间:2019-04-10 11:39:34

答案(点此获取答案解析)

A

同类题4

完形填空

    My parents used to tell me how important the school was for me, but I didn’t think so. I didn’t   1    it. What I cared most was to hang out with my friends. But one thing let me finally  2  what my parents meant.

    One day, when I walked3a cellphone store, I saw an advertisement on its door. It was hiring(雇佣) new workers!

    “Sir, are you hiring people?” I went into the shop and asked. “Yes, but you  4 be the man who we need.” the manager answered. He looked at me for a few minutes from head to 5 .” Do you have a high school diploma(文凭)?”he asked, “do you have any working  6 ?”

    I felt so ashamed and  7  that I didn’t know what to say, so I just turned around and left.

I could not fall asleep that night, and I thought a lot about my future. “I must go to school  8  I can’t do anything without a good education,” I said to myself. I never went back to the store9  before I finished my study and got a diploma.

    Everything looked the same when I returned to the10: the same people and the same design. However,  11 with last time, I had more confidence this time. So it was a great chance for me.

I12  my diploma to the manager who once refused me. He looked at  13 for a while and then said to me, “Great, you are in.”

    Now I am still working in the same store. With this experience, I  14advise teenagers to attend to school. Education helps you have a bright future. Now I am not worried about my future because I still keep 15  in my free time. Education brings my future, doesn’t it?