Compressed Tanks

The mass of each gas can be determined by the ideal gas law:

     m = pV/RT

For oxygen, the gas constant R is 0.2598 kJ/kg-K. The mass of the oxygen in a single tank is

     m = (1000)(0.25)/(0.2598)(290)
        = 3.318 kg

For nitrogen, the gas constant R is 0.2968 kJ/kg-K. The mass of the nitrogen in a single tank is

     m = (850)(0.25)/(0.2968)(290)
        = 2.469 kg

For carbon dioxide, the gas constant R is 0.1889 kJ/kg-K. The mass of the carbon dioxide in a single tank is

     m = (1,250)(0.25)/(0.1889)(290) = 5.705 kg

The total weight of the tanks is then given by

W_total = weight of empty tanks + weight of gases
          = (15)(5)(9.8) + (5)(3.318)(9.8)
                 + (4)(2.469)(9.8) + (6)(5.705)(9.8)
          = 1,330 N