A vertical cylinder fitted with a heavy leak-proof piston wi

[CLARA]

Homework Statement

HERE IS THE QUESTION
A vertical cylinder fitted with a heavy leak-proof piston with diameter 84.0 mm contains air (under the piston) of density 1.59 kg/m3 in thermodynamic equilibrium with the surrounding atmosphere, which is at 100 kPa and 39 oC. Determine the mass of the piston in kg, to three significant figures. Use gravitational constant g = 9.81 m/s2.[/B]

Homework Equations

i tried to use PV=mRT for the air in the cylinder[/B]

The Attempt at a Solution

mg= PA
I know there is a force due the the piston and the force due to the air
F_PISTON = F_AIR
F_PISTON = mg
F_AIR THIS IS WHERE IM STUCK IM NOT SURE IF MY WHOLE LOGIC FOR THIS QUESTION IS CORRECT. YOUR HELP IS GREATLY APPRECIATED[/B]

 

[Delta2]

I am a bit confused by your naming/labelling of the forces and the equations you write.

To clear this :
There are three different forces that are acting on the piston. Which are these three forces?