F.6 AL Physics - Statics

Part (b)
Let d be the required distance from X
When the planck is about to tip, the normal reaction at Y is zero
hence, taking moment about X,
700d = 100 x 2
d = 200/700 m = 0.286 m
The reaction at X = (700+100) N = 800 N
Reaction at Y = 0 N