How Do You Solve Adiabatic Process Problems Involving a Piston and Sand?

[sheyshaw]

An insulated cylinder of cross-sectional area .010m2 contains a monatomic ideal gas at T= 280 K. The system is in a vacuum chamber. Initally the gas supports the piston at a height of .20m. Sand is slowly placed onto the piston. When 10 kg of sand has been added, the piston has fallen .05m. How much gas is in the cylinder? what is the mass of the piston?

Im having difficulty getting started

Can i equate the work done by gravity with the work done by the gas?

 

[mbrmbrg]

Isn't this more of a chemistry problem? There's another thread for chem.; you might have more luck over there.

 

[sheyshaw]

No its right out of a physics book! Its a thermodynamics problem

 

[sheyshaw]

Im getting 66.34 kg can someone confirm this

 

[mbrmbrg]

Ouch. My bad.

 

[Andrew Mason]

Im getting 66.34 kg can someone confirm this

Explain your work and we will review it.

AM

 

[sheyshaw]

Review this:

I plan to solve the problem using the fact that the work done by gravity on the gas will equal the change in internal energy.

I reason this because Q = u + W

The process is adiabatic so u = -w

does that work?

 

[Andrew Mason]

Review this:

I plan to solve the problem using the fact that the work done by gravity on the gas will equal the change in internal energy.

I reason this because Q = u + W

The process is adiabatic so u = -w

does that work?

How do you calculate the work done by gravity? The sand is gradually adding to the weight as the gas is compressing.

You can determine the final volume of the gas. You can assume that no heat is exchanged with the environment, so it is adiabatic. I would use the adiabatic condition to determine the final temperature.

AM