A mountain-climber friend with a mass of 80 kg ponders the idea of attaching a helium-filled balloon to himself to effectively reduce his weight by 25% when he climbs. He wonders what the approximate size of such a balloon would be. Hearing of your physics skills, he asks you. Share with him your calculations that show the volume of the balloon to be about 17 m3(slightly more than 3 m in diameter for a spherical balloon).

Solution Step 1 of 3 According to archimedes principle of buoyancy, when the body is completely or partially immersed in a fluid(gas or liquid) at rest; is acted by an upward force called buoyant force. Which in magnitude equal to the weight of the fluid. Buoyancy = weight Since weight= volume×density of fluid Buoyancy = volume×density of fluid F = V× fluid