A balloon is 4 m in diameter and contains helium at 125 kPa and 15°C. Balloon material and payload weigh 200 N, not including the helium. Estimate
(a) The terminal ascent velocity in sea-level standard air;
(b) The final standard altitude (neglecting winds) at which the balloon will come to rest; and
(c) The minimum diameter (<4 m) for which the balloon will just barely begin to rise in sea-level air.