# Homework Help: Rotational Equilibrium Help!

1. Aug 20, 2009

### alexo

1. The problem statement, all variables and given/known data
I think I'm being a bit dull today but I seem to be having real trouble understanding this question...

Two children wish to make a see-saw from a 5m plank of wood, the children weigh 25kg and 20kg. They wish to sit right on the ends of the plank. Where should the plank be supported in order for it to balance...

2. Relevant equations
t=RF

3. The attempt at a solution
I know that Net ACWM should = CWM...
I found the weight in Newtons of the kids...196N and 245N..
I added the two forces together to get the opposing force of the pivot, 441N

But now i'm stuck... and have no idea where to take it from here :(

Thanks :) Alexo.

2. Aug 20, 2009

### LBloom

I dont think the question is dealing with the pivot (in many of these problems the means of rotation, like the pulley is deemed massless and frictionless.)
the question is about torque, so ask yourself, how can the plank be placed so there is no torque? the only equation you need you already have.