A thin 2kg box rests on a 6kg board 50cm long with 20cm hanging off the edge of a table. How far can the center of the box be from the end of the table before the board begins to tilt?

Answer 1

If you assume the cg of the board is at the center, then summing moments from the end of the board on the table.
L= length of box from edge of table.

2kg*g*L+ 6kg*g*25cm-(8kg*g*30cm)=0

solve for L. NOtice I put the force of the table at the edge, which is true if the board is fixing to rotate and the box falls.

Answer 2

According to the above reference the answer would be 45cm yes? - which doesn't make sense because there is only 20cm of board from the end of the table. And i'm not exactly sure where the 25cm came from? Can someone please expand on this answer?