A uniform plank weighing 50N and 12m long is pivoted at a point of 4m from one end.A boy weighing 30N sits on a plank 7m from pivot.where must his elder brother whose weight is 80N sit to balance the plank horizontally

Answer 1

50/3 * 2 + 80*d = 2*50/3 * 4 + 30*7
d = 31/8 m