1. Calculate the net force (which would include the force of gravity and the force of buoyancy) acting on a spherical helium-filled balloon in air with radius R=12 cm. The mass of the empty balloon shell is 3.2 g, density of air is PAIR=1.3 kg/m, and the density of helium inside the balloon is PH-0.18 kg/m. What is the direction of the net force? 1 kg = 1000 g, 1 m = 100 cm. Volume of a sphere V=(4R/3) 2. Calculate the additional mass that needs to be attached to the balloon described in the previous problem to reach mechanical equilibrium (a condition when the force of buoyancy and the force of gravity are equal in magnitude).