Question

A piston/cylinder,  contains air at 1380 K, 15 MPa, with V₁ = 10 cm³, Acyl = 5 cm². The piston is released, and just before the piston exits the end of the cylinder the pressure inside is 200 kPa. If the cylinder is insulated, what is its length? How much work is done by the air inside?  

Answer 1

V. Air, Cylinder is insulated so adiabatic, Q = 0.

Continuity Eq.: m₂ = m₁ = m,

Energy Eq. m(u₂ - u₁) = ₁Q₂ - ₁W₂ = - ₁W₂ 

Entropy  m(s₂ - s₁) = ∫ dQ/T + ₁S₂ gen = 0 + ₁S_{2 gen} 

State 1: (T₁, P₁) 

State 2: (P₂, ?) 

So one piece of information is needed for the ?, assume reversible process.