# Determine pressure of a gass in a piston-cylinder device

#### v_pino

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

#### Ofey

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

### The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving