A helium-filled balloon is attached by a string of negligible mass to a small 0.015 kg object that is just heavy enough to keep the balloon from rising. The total mass of the balloon, including the helium, is 0.0050 kg. The density of air is
air = 1.29 kg/m
3, and the density of helium is
He = 0.179 kg/m
3. The buoyant force on the 0.015 kg object is small enough to be negligible.