Equilibrium physics problems

[gnarrr]

http://img27.imageshack.us/img27/8011/physicsproblems.png

 

[rl.bhat]

Hi gnarrr, welcome to PF.
Please go through the rules of the PF.
Don't post the problems alone. Show your attempts. List the relevant equations. Still if you don't get, we will help you.

 

[gnarrr]

The first one

Homework Statement

Consider the bar to have negligible mass. How far from point 'A' must a downward force of 40.5 N be applied in order to achieve rotational equilibrium.

Homework Equations

T1=T2
F=0

The Attempt at a Solution

5x9.8x2.1 + 3.5x9.8x4.3 + 40.5xd = 0
d=6.18m

 

[gnarrr]

i figured out the second one

 

[rl.bhat]

First on is wrong.
If you want to take the moment about the fulcrum, you have to consider clockwise and counterclockwise moments and use proper sings.
If you want to take the moments about A, 40.5 N and 3.5 kg produce clockwise moment and the reaction due to all the forces on the fulcrum will produce the counterclockwise moment. Equate them to get d.