§3-1Work(功) 1. Work done by a constant force The work done by F is iven by g 0 0 W=(F 0)S(3-1) orl W=F.S(3-2) The si unit of w is joule 1Joule=1J=IN m=1kg.m2/s2§3-1 Work（功） 1. Work done by a constant force  F   F  s The work done by is given by F  W F S   =  (3-2) W = (F cos )S (3-1) (or) The SI unit of W is Joule : 1Joule =1J = 1N·m = 1kg·m2 /s2