Find the magnitude of FB?

[769]

I cant seem to figure out where to start on this one and any help would be appreciated.

Thanks.

[Nathan Kiranov]

(a)

The thing to notice here is that if the resultant force is perpendicular to the
wall then the vertical components of FA and FB must cancel. The vertical
component of FA is up(+) and the vertical component of FB is down(-).

FA.y + FB.y = 0

FA.y = |FA|*sin(50)
FB.y = -|FB|*sin(70)

FA.y + FB.y = |FA|*sin(50) - |FB|*sin(70) = 0
|FB|*sin(70) = |FA|*sin(50)
|FB| = |FA|*sin(50)/sin(70)
|FB| = 81.52 N ............................. Answer (a)


(b)

FB = |FB|*cos(70) - j*|FB|*sin(70)
FB = 27.9 - j*76.6 N ...................... Answer (b)