- #1
pinkerpikachu
- 29
- 0
Homework Statement
How many helium-filled balloons would it take to lift a person? Assume the person has a mass of 76 kg and that each helium-filled balloon is spherical with a diameter of 33 cm.
Homework Equations
P = P0 + ρgV
The Attempt at a Solution
I really don't know why this is confusing me, since it seems pretty straight forward. But, I know that the buoyant force has to be equal to at least the mass of the person (M) + the mass of the helium in all the balloons (m)
which means that FB = Mg + mg
and the buoyant force is due to the helium, so, in order for the person to be lifted,
ρHegV = Mg + mg
so ρHeV = M + m
which is
ρHeVHe = M + ρairVHe
right?
So then M/(ρHe - ρair) = V
but this would be negative...What I am doing wrong?
(I don't need help with the last part which is finding the number of balloons)
thanks!