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Topic: Pressure Inside of A Container  (Read 2726 times)

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Offline Kramer55

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Pressure Inside of A Container
« on: September 16, 2008, 10:26:29 AM »
I have been given a question about the pressure of a cylinder and how it affects a piston that rests on two stoppers.

A cylinder has a piston resting on top of two blocks; the two blocks do not allow the cylinder to move down, but the pressure can force the piston upwards. The pressure inside the cylinder is 60kPa and 373 Kelvin. The diameter of the piston is 0.1 m with a mass of 10 kg. The pressure outside of the cylinder is 100 kPa and the temperature is 293 Kelvin. The cylinder is heated.
At what temperature does the piston just rise upwards from the blocks?

I figured out the volume of the cylinder by using pV=nRT for the cylinder. Then I tried using the following equation:
P(system) = P(external) + (mass(piston) * gravity)/Area   

I then used that pressure value (224 kPa) and plugged that into P(system)*V = mRT and solved for T. I got an answer of 1389 K, which I am fairly certain is way too high of a temperature.

So I am not too sure where to go after this point. Thank you for any *delete me*

Offline Yggdrasil

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Re: Pressure Inside of A Container
« Reply #1 on: September 16, 2008, 10:35:16 AM »
I get a different value for P(system).  Can you show your work so that we can figure out how the calculation went wrong?

Offline Kramer55

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Re: Pressure Inside of A Container
« Reply #2 on: September 16, 2008, 10:49:56 AM »
Thanks for the quick reply.

For P(sys) = P(ext) + [mass(piston)*grav]/Area

P(ext) = 100kPa
Mass(piston) = 10 kg
Gravity = 9.81 m/s2
Area = pi * 0.052 = 0.0079 m 2

Am I using the wrong equation for area?

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