问题
计算题
飞鹰同学用如图所示的滑轮组,将重200N的物体在10s中匀速提高了2m,手的拉力是120N。问:
(1)有用功是多少?
(2)总功是多少?
(3)机械效率多大?
(4)总功的功率多大?
答案
解:
(1)W有 = Gh =200N×2m = 400 J
(2) W总 = FS =120N×2×2m = 480 J
(3)η = W有/ W总 = 400 J/480J=83.3%
(4)P=W总/t = 480J/10s = 48w