19) 700 N
This requires the knowledge of Moments (physics term).
In order for the bar to be in equilibrium, Moments clockwise = Moments anticlockwise
Moments = F x perpendicular distance
Moments anticlockwise = 1.5 x 1000 = 1500 Nm
Moments clockwise = 100 x 4.5 = 450 Nm
Moments required = 1500 – 450 = 1050 Nm
Total length of the bar = 1.5 + 4.5 = 6 m
Since the weigh of the bar acts on the middle, the weight would act at (6 ÷ 2) = 3 m
Distance of weight from the pivot = 3 – 1.5 = 1.5m
Moments required = 1050 Nm
1050 = F x 1.5
F = 700 N
Hence weight = 700 N