How Do You Calculate Forces on a Plank with Unevenly Placed Weights?

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SUMMARY

The discussion focuses on calculating the forces acting on a uniform plank with a weight of 120 N and an additional weight of 80 N placed midway between two stools. The correct forces acting on the stools at points A and B are 80 N and 120 N, respectively. Initial calculations yielded incorrect values of 88 N and 112 N for the forces at A and B. The key equation used is the moment equation, which states that the turning effect equals the force multiplied by the distance from the pivot.

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Moment -- A weight on a plank

Homework Statement



A uniform plank of weight 120 N rests on two stools as shown in the link provided below. A weight of 80N is placed on the plank, midway between the stools. Calculate the force acting on the stool at A and B. The answer is 80N and 120 N respectively. I calculated the answers to 88N and 112N.

The image link : http://imageshack.us/photo/my-images/864/moments.png/


Homework Equations



Turning effect = Force * Distance from the pivot

The Attempt at a Solution



(80*1.25) + (120*1.5) = FB * 2.5
FB = 112N

(80*1.25) + (120*1.0) = FA * 2.5
FA = 88N
 
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welcome to pf!

hi psychicgerm! welcome to pf! :smile:
psychicgerm said:
(80*1.25) + (120*1.5) = FB * 2.5
FB = 112N

(80*1.25) + (120*1.0) = FA * 2.5
FA = 88N

it isn't 1.25 :wink:
 

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