The pressure 
of an ideal gas is given by the expression
where 
is the density of the gas.
State the meaning of the symbol 
.
Use the expression to show that the mean kinetic energy 
of the atoms of an ideal gas is given by the expression
Explain any symbols that you use.
Helium-4 may be assumed to behave as an ideal gas. A cylinder has a constant volume of 
and contains helium-4 gas at a pressure of 
and at a temperature of 
. Calculate, for the helium gas,
the amount of gas,
the mean kinetic energy of the atoms,
the total internal energy.
