There's a problem in my thermo class that I think I have the right answer for, but the value I get doesn't seem to make sense. The problem reads: Warm air is contained in a piston-cyliner assembly oriented horizontally. The air cools slowly from an intial volume of .003 m^3 to a final volume of .002m^3. During the process, a spring exerts a force that varies linearly from an intial value of 900N to a final value of zero. The atmospheric pressure is 100kPa, and the area of the piston face is .018m^2. Friction between the piston and the cylinder wall can be neglected. For the air, determine the intial and final pressures, in kPa, and the work in kJ. So I split the system up into two states. State 1: V1 = .003 m^3 Fspring = 900N State 2: v2 = .002 m^3 Fspring = 0N I found the pressures for each state using a force balance equation and the relationship between force and pressure. I came up with: Fair = Fspring + Farm (Pair)(Apiston) = Fspring + (Pair)(Apiston) Using the values for State 1 and 2 I came up with 150 kPa for State 1 and 100 kPa for state 2. Here's where I run into problems. Calculating the work. First off I make the assumption that the magnitude of the work done as the spring moves is equal to the magnitude of the work the air does during this change. Therefore, I used 1/2kx^2 for work done. I found the distance the spring moved using (V2-V1)/Apiston = delta X Using this x value I went to Fspring = 900 = kx and found k. From here I used evaluated 1/2kx^2 and I came up with an answer of 25Joules. My question is, is the answer I getting make sense physically, because it seems like a really small answer, also are the assumptions I am making for work done correct, or is there another way I should go about this.