In thermodynamics, how do you know if pressure is constant, volume is constant, PV is constant or PV^n is constant when going through a problem. I know that a rigid vessel means constant volume, any other tricks I can use to distinguish between each because while reading a problem I just have no clue. Also any advice on how to go about solving problems? This class is literally making me go crazy!
An example problem would be something like:
An air pistol contains compressed air in a small cylinder, shown in Fig. P5.134. Assume that the volume is 1 cm3, pressure is 1 MPa, and the temperature is 27°C when armed. A bullet, m = 15 g, acts as a piston initially held by a pin (trigger); when released, the air expands in an isothermal process (T = constant). If the air pressure is 0.1 MPa in the cylinder as the bullet leaves the gun, find
a. The final volume and the mass of air.
b. The work done by the air and work done on the atmosphere.
c. The work to the bullet and the bullet exit velocity.
Another example problem would be like:
A piston/cylinder has 0.5 kg air at 2000 kPa, 1000 K as shown. The cylinder has stops so Vmin = 0.03 m3. The air now cools to 400 K by heat transfer to the ambient. Find the final volume and pressure of the air (does it hit the stops?) and the work and heat transfer in the process.