A one kg non-stretch balloon fabric on the ground (Po= 1 bar) is attached to a 2 kg payload. One kg of helium is placed into the balloon. How many pounds of restraint are needed to keep the assembly tethered to the ground? When the restraints are cut how high does the assembly go in an isothermal atmosphere at -10 C? The balloon fabric can inflate to a maximum radius of five meters. At what altitude does the balloon.reach its maximum inflation? The balloon keeps rising past this height when it reaches maximum inflation and finally stops. Why does it stop? What is the pressure of the helium inside the balloon when it reaches its maximum altitude? If a little helium is released will the balloon go up or down? A 1 kg non-stretch balloon fabric on the ground (Po=1 bar) is attached to a 2 kg payload.