用如图所示的机械拉着400N的物体在水平地面上匀速运动，物体受到的摩擦力为100N，绳子末端的水平拉力为50N，则滑轮组的机械效率为____。若物体运动的速度为0.2m/s，则10s内拉力做功____J。

    Good evening, everyone! Today, I'm very glad1a speech2name is "My Dream". We know everyone has his or her own dream. Some people want to be basketball players because they are good3sports. Some would like to become4 because they like to stay with children. Do you know5I'm going to be when I grow up? I like cooking,6 I want to become a good cook. I think I must have great7 cooking food. I'd like to ask everyone to taste my food. I also like seeing their smiling faces after8the delicious food. However, it's not so9to be a good cook. I decided to learn 10things about cooking from now on. I will work hard for my dream. I'm sure I will succeed (成功) one day.