Answer:
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
