U-shaped tube, pressure problem, what am i doing wrong?

[jenzao]

Homework Statement

What am I doing wrong in this pressure problem?
a U-shaped tube is filled with water.
left side area of opening is .05m^2
right side is .08m^2
the right side water level is .43m HIGHER than the left side, because two pistons push down on either side with different force on each side.
the force pushing down on right side is 138N

Q: What is the force pushing down on left side?

Homework Equations

I know that P=F/A and also P= Pnaught + rho*g*h

The Attempt at a Solution

so i rearrange to get F=PA
and P=rho*g*h (because i can factor out air pressure (Pnaught) because of the pistons,
so i now have F= rho*g*h*A
This is wrong though, and i can't figure out why, please help! thanks

 

[mgb_phys]

You are looking for the extra pressure needed to make the side 0.43m higher
So you need the pressure to lift 0.43m of water, this is just the static pressure at the bottom of that extra water column.

The extra pressure on the input piston is the same as this - then to get the force just use the area - be carefu about which area you are using.