Statics: A mother would like to balance her son on the teetor totter

A mother would like to balance her son on the teetor totter. Calculate the distance "d" so that the system is in equilibrium. Also calculate the reaction at point O.

Solution

↻+ (clockwise positive)

↻+ΣMo = 0

-120lb (d) + 43lb (4ft) = 0
d = 1.433 ft

→+ΣFx = 0

Ox = 0

↑+ΣFy = 0
-120lb + Oy - 43lb = 0
Oy = 163 lb