Determine pressure of a gass in a piston-cylinder device

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1. The problem statement, all variables and given/known data

A gas contained in a vertical frictionless piston-cylinder device. The piston has a mass of 4kg and a cross-sectional area of 35 cm^2. A compressed spring above the piston exerts a force of 60N on the piston. If the atmospheric pressure is 95kPa, determine the pressure inside the cylinder.

Ans: 123400 Pa

2. Relevant equations

P = F/A

P (at depth h) = density * g * h + atmospheric pressure


3. The attempt at a solution

Total force = (4g+60)

P (at depth h) = ((4g+60) / (0.35)) + (95000)

= 95284 Pa (which is not what the answer gives.)

many thanks
 
75
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Re: Pressure

One error, you haven't changed 35 cm^2 to m^2 properly. Try using 35x10^-4 m^2 and you get the right answer. A pretty good trick to do it if you can't remember how many "steps" you move the ,/. sign is

cm^2 = cm x cm = (1/100)m x (1/100)m = (1/100)^2 m^2 = 10^-4 m^2
 

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