1. The problem statement, all variables and given/known data An empty rubber balloon has a mass of .0120 kg. The balloon is filled with helium at a density of .181 kg/m^3. At this density the balloon is spherical with a radius of .500m. If the filled balloon is fastened to a vertical line, what is the tension in the line? 2. Relevant equations Equations that I found: volume of a sphere = 4/3(pi)(r^3) density = mass/volume Buoyant force = weight 3. The attempt at a solution I attempted to set up a free body diagram, with two forces. One is the tension going up, and the other is weight going down. That would mean T = mg. since density = mass/volume, .181 kg/m^3 = mass / (4/3)(pi)(.5)^3. That gets a mass of .095g. .095g(9.8 m/s^2) = .929 N. The correct answer is 5.57 N. So, I got it wrong.