The spherical weather balloon is filled with hydrogen till its radius is 3.00 m. Its total mass comprising the instruments it carries is 13.0 kg.
(i) Determine the buoyant force acting on the balloon, supposing the density of air is 1.29 kg/m3.
(ii) Determine the total force acting on the balloon and its instruments subsequent to the balloon is free from the ground?
(iii) Explain why does the radius of the balloon tend to rise as it rises to higher altitude?