find magnitude of F so that the resultant couple moments is

find magnitude of F so that the resultant couple moments is equal to 700Nm clockwise. it\'s hard to get a clear picture of my work but

I\'m not sure what I did wrong.

Solution

Drop a ^_r from the verex to the base , OM,

The traingle is an isoceless one , ÐA = ÐB = 40⁰

^{AM= BM = 0.5}

From OMB , Cos(40) = MB/OB

Arm of the couple F = OB =OA= MB/Cos(40) = 0.5/0.77 = 0.653

F and 250N produceCW moments, whereas 600N produce CCW moment

Moment of the couple = F*OB

Resultant moment =

250*1+F*0.653-600*0.653 = 700

F = 641.8/0.653    =   982.85 N