题干

如图所示,小华用此滑轮组将重为3N的物体匀速提升0.1m所用时间为2s,所用的拉力为1.2N,不计绳重及摩擦,下列说法正确的是(  )

A:绳子自由端移动的速度为0.05m/s

B:拉力F的功率0.36W

C:滑轮组的机械效率约为83.3%

D:匀速上升过程中物体的机械能不变

上一题 下一题 0.0难度 选择题 更新时间:2019-07-25 04:20:30

答案(点此获取答案解析)

C

同类题4

完形填空

    As a child, I started learning to play the piano, my favorite musical 1 but I was forced to give up when I started my middle school2 I could concentrate more on my studies.

    It's one of my biggest3 to stop practicing the piano when I recall sadly today. During the following years, I kept telling my piano teacher that I would4However, I didn't keep my promise because I was 5 with my study6 I lost touch with my teacher. Some years later, my teacher died. I was very sad because I lost such a good teacher. She was a very warm and gentle person. It hurts me to think she may have been 7 that I never returned. I haven't taken lessons since then but to be honest, I 8 to. Sitting at the piano, I couldn't help recalling many 9 ---times of my practising at home and playing before my teacher and one time my teacher 10 me after I played entire pieces of music wrong in front of her colleagues. I was so 11 that I could hardly say anything. But her 12helped ease my shame. These memories13good or bad, never caused my14 for playing the piano again.

    This thought then led me to think that 15 is like music, and that we all try to play different 16 in the instrument of our life. Sometimes the pitch (音高) is17when we play it well, but sometimes we are out of tone. However, we all continue to create our own 18style of music. No matter what style our music is, it is 19 that we sing the songs of joy, quietness and love. Though I may never make it back to piano lessons, it doesn't 20 that I've stopped making music.