buoyant forces I was having trouble with this problem. please let me know how to approach this. thanks. An empty rubber balloon has a mass of 0.0135 kg. The balloon is filled with helium at a density of 0.181 kg/m3. At this density the balloon is spherical with a radius of 0.400 m. If the filled balloon is fastened to a vertical line, what is the tension in the line?