Calculating Work Energy Input for Compressing Air in a Piston-Cylinder Assembly

[freshbox]

A piston-cylinder assembly contains 20kg of air with a specific internal energy of 28K J/kg. It is compressed to a high pressure and the final specific internal energy is 65K J/kg. During the process there is a heat loss of 3.2K J. Determine the work energy input needed for the compressor.


Just want to ask how come I need to use the mass times the internal energy? What's the concept behind?



Thanks.

 

[BruceW]

You have been given the "specific internal energy". This is different to the "internal energy". And the question asks for a calculation of energy. So you need to calculate the internal energy by using the specific internal energy. I think you have already guessed how to do that.

 

[freshbox]

oops... why didn't i see that haha... anyway thank you Mr Brucew :)

 

[BruceW]

ha, no worries. It is easy to miss.