Determine the weight of a ruler using only a weight?

Question

I'm an idiot apparently.  In my physics lab, we had a ruler and a 100g weight and we had to determine the weight of the ruler.  I thought this was no problem and put the weight on top of the ruler and then pulled the ruler out from the edge of the table until it was just about to fall, but not quite and recorded how far out I had pulled it.

I thought that I could then use mass*length on one side equals mass*length on the other side to get the equation.  It was 66 centimeters sticking out, with the weight 10 centimeters from the pivot point (edge of the table).

I weighed the ruler to make sure I could check my answer, but my answer is way off and now I'm at a loss for what to do.  .66*M=.1*.1 would mean that the ruler weighs .022 kilograms, but it should weigh around .3 kilograms.

If anyone would please tell me where I'm going so horribly wrong, I would be most grateful.

Rahil Momin · Accepted Answer

well the mass*length on one side = mass*length on the other side works only if the rules is massless.
for rulers with mass, you have to take something into account which is known as moment of inertia and then apply the law,
torque on one side is equal to torque on the other side.

apply on your own, 
believe me, when you do such things on your own,
it feels great, and you get a great boost of self-confidence
it may now appear dumb, but experience will tell better

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Determine the weight of a ruler using only a weight?

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