Question

Calculating Pressure

In my Thermodynamics book (6e Moran), I'm having a problemwith 1.42. The problem states as follows:"Warm air is contained in a piston-cylinder assembly orientedhorizontally. The air cools slowly from an initial volume (V1) of0.003 m^3 to a final volume (V2) of0.002 m^3. During the process,a spring exerts a force that varies linearly from an intial valueof 900 N to a final value of zero. Patm = 100 kPa and Area (A)=0.018 m^2. Friction is ignored. Find inital pressure and finalpressure, in both kPa and atm."I know I should use P1 = Patm + (force of spring/A) and samefor P2 (at least I think so). My problem is what to do about theforce of the spring! The diagram statesthat the "Spring forcevaries linearly from 900 N when V1 = 0.003 m^3 to zero whenV2 = 0.002 m^2". So I know volume is important in finding P1and P2 but I don't know how (or maybe it's not at all as someothers have told me!) So, confused…Please help me. 🙂

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