How many helium-filled balloons would it take to lift a person? Assume the person has a mass of 80kg and that each helium-filled balloon is spherical with a diameter of 33 cm.?

It is necessary 3815 balloons to lift a person of 80 kg

Explanation:

Knowing that

density of air ρa = 1.293 kg/m³

density of helium ρh = 0.1786 kg/m³

Each balloon has

V = πd³/6 = π (0.33m) ³ / 6 = 0.0188 m³

So,

the "lift" for each balloon is

L = (ρa - ρh) Vg = (1.293 - 0.1786) kg/m³ * 0.0188m³ * 9.8m/s² = 0.2055 N

This way,

the number of balloons n = 80kg * 9.8m/s² / 0.2055N/balloon = 3815