A 75-kg adult sits at one end of a 9.0-m-long board. His 25-kg child sits on the

Question:

A 75-kg adult sits at one end of a 9.0-m-long board. His 25-kg child sits on the other end.
(a) Where should the pivot be placed so that the board is balanced, ignoring the board’s mass?
(b) Find the pivot point if the board is uniform and has a mass of 15 kg.