(a) Show that internal energy of an ideal gas is expressed as
`U=(PV)/((gamma-1))` when `P=`pressure, `V=`volume and `gamma=(C_P)/(C_V)`.
(b) Hence find the internal energy of air in a room of volum `50m^3` at atmospheric pressure.
`(1Atm=10^5(N)/(m^2))`