(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

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.

2. Relevant equations

P = P_{0}+ ρgV

3. 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 F_{B}= Mg + mg

and the buoyant force is due to the helium, so, in order for the person to be lifted,

ρ_{He}gV = Mg + mg

so ρ_{He}V = M + m

which is

ρ_{He}V_{He}= M + ρ_{air}V_{He}

right?

So then M/(ρ_{He}- ρ_{air}) = 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!

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# Homework Help: How many helium balloons does it take to lift a person?

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