A uniform plank of length 6.00m and mass 30.0 kg rests horizontally across two horizontal bars of a scaffold. the bars are 4.50 m apart, and 1.50m of the plank hangs over one side of the scaffold. How far can a painter of mass 70.0kg walk on the overhanging part of the plank before it tips? This is really confusing me. I have the forces identified: mg going down, normal force up, and the weight of the man going down. Im guessing the equation to solve this would look something like n-mg-70kg(d)=0...I really dont know how to incorporate the lengths into it.