The pressure of a gas inside a piston-cylinder device is initially balanced by a

Question

The pressure of a gas inside a piston-cylinder device is initially balanced by an atmospheric pressure of 100kPa and an elastic linear spring. The initial volume of the gas in the cylinder is 32e-6 m^3. Initially, the spring is uncompressed and exerts no force on the piston. The area of the weightless piston is 0.0004 m^2. Heat addition to the gas causes the piston to rise by 2 cm. k is 10 N / cm.

Determine the final absolute pressure (kPa) of the gas.

Neglecting work due to friction and atmospheric pressure, calculate the work (J) during expansion.

Please explain!!

Explanation / Answer

Final absolute pressure = Atmospheric pressure + Spring "pressure"
= 100 kPa + (10 N/cm x 2 cm / 4 cm2)
= 100 kPa + 50 kPa
= 150 kPa
Change in internal energy
= -(0.5 x 10 x 2 x 2) J + 7 J
= -13 J

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