A mass of 105 kg is placed on the piston of a vertical pisto

A mass of 105 kg is placed on the piston of a vertical piston-cylinder device containing nitrogen. The piston is weightless and has an area of 1.15 m2 . The outside pressure is 100 kPa. Assume temperature to remain constant at 310 K and R for nitrogen to be 0.296 kJ/kgK. a) Determine the pressure inside the cylinder. b) The mass placed on the piston is now doubled to 210 kg . Also, additional nitrogen is injected into the cylinder to double the mass of nitrogen. Determine the pressure inside under these changed conditions.

Solution

a) The weight of the 105-kg mass is 1030.05 N,

pressure = force/area = 1030.05/1.15 = 895.69 N/m^2 = 895.69 Pa
so the pressure in the cylinder is 0.89569 kPa + 100 kPa= 100.89569 kPa

(b) The weight of the 210-kg mass is 2060 N,

pressure = force / area = /1.15 = 1791.39 N/m^2 = 1.79139 kPa
so the pressure rises to 1.79139 kPa + 100 kPa = 101.79139 kPa

The temperature and the R-value are not needed.