— What ____ your parents do?
— They are ____.
在下列情境中,你会怎么做?并说出你的理由。
— Could you please tell me ________?
— Of course. Many people in Wuwei know it.
在郾城大战中大败金军,倍秦桧以所谓“谋反”罪杀害的南宋抗金名将是( )
工人用如图所示装置从6m深的井中匀速吊起一个重量是800N的物体,若每个滑轮重为200N,2min后物体由井底升至井口.求:(不计绳重及摩擦)
(1)物体上升过程中工人所做的有用功功率;
(2)滑轮组的机械效率.