# Static equilibrium problem

1. Oct 8, 2005

### Kenny Lee

The problem is stated as follows:

A uniform plank with a length of 6.00 m and mass 31.0 kg rests horizontally across two horizontal bars of a scaffold. The bars are 4.50 m apart, and 1.50 m of the plank hangs over one side of the scaffold.
How far can a painter with a mass of 68.0 kg walk on the overhanging part of the plank before it tips?

Its a simple problem. We just fix up an equation that describes eqbm about the second scaffold (from the man and the center of mass) and we get a result of 0.684...

But I was wondering why we don't consider the normal reaction at the other scaffold? Shouldn't there be an upwards force contributing towards an ACW moment at that point... why don't we include it in calculations? I need help. Anyone please.

2. Oct 8, 2005

### Pyrrhus

Because when the painter starts going at certain distance the planck won't be supported by that scaffold, it'll start lifting, but still in equilibrium at a certain position of the painter in the planck.

3. Oct 8, 2005