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**Hi guys,**

i just discovered this forum and this is my first post so apologies if i made any mistake with the how I am suppose to structure a thread. but nontheless any help would be greatly appreciated!

cheers

1. Homework Statement

i just discovered this forum and this is my first post so apologies if i made any mistake with the how I am suppose to structure a thread. but nontheless any help would be greatly appreciated!

cheers

1. Homework Statement

4. A 250mm diameter insulated cylinder (see figure below) is fitted with a frictionless, leakproof piston, which is attached to an unstressed spring S (spring constant, k = 175kN/m). The cylinder is connected by a closed valve to the mains pipe, in which air flows at a high pressure and a temperture of 27°C. The spring side of the cylinder is open to the atmosphere (Patm = 101kPa).

The valve is now opened slowly permitting air to move the piston through a distance of 150mm, thus compressing the spring. At this point the valve is closed, trapping air in the cylinder.

a) Write down the 1st law of thermodynamics for an open system and simplify it for this charging process, which can be assumed to be adiabatic. b) Calculate:

i) The final pressure of the air in the cylinder.

ii) The final temperature of the air in the cylinder.

iii) The mass of air injected into the cylinder.

answers:

[636kPa, 340.8K, 0.0479kg]

## The Attempt at a Solution

i've managed to get the first answer of P

_{2}. but I am stuck on the 2nd part. am i suppose to use

P

_{1}/T

_{1}=P

_{2}/T

_{2}

any help would be appreciated!