Jawabanmu

2014-04-14T16:43:29+07:00
W = F.S
    = 400 . 1200
    = 480000 joule
2014-04-14T16:47:32+07:00
W (usaha) = F x s = 400 x 1200 = 480000 J/kg
f = 400 N
s = 1,2 km = 1200 m