A 70kg adult sits at one end of a 10m board, on other end sits a 30kg child. where should pivot point be placed so board is balanced? board's mass is 15kg. so far, i have pivot point is 15kg(9.8)=147N (5) <-- half the board length.. for adult i have 686N and kid is 294N. i know that Etorqueccw=Etorquecw ... but im not sure how to use that for the lengths of both humans, since there are 2 variables. need two eqns then rite? but whats the other eqn?..