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

[psychicgerm]

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) = F_B * 2.5
F_B = 112N

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

 

[tiny-tim]

welcome to pf!

hi psychicgerm! welcome to pf!

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

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

it isn't 1.25