# Physics

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Hey can someone help me out? I only have 1 attempt left on this question and do not understand it at all!!!

A 3.5 kg balloon is filled with helium ( density = 0.179 kg/m^3).
If the balloon is a sphere with a radius of 5.2m , what is the maximum weight it can lift?

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What is the weight of the air it displaces (volumeair*density*g) minus the weight of the balloon (mg)?

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So volume of balloon 4/3*pi*r^3 *density of helium * g - ( 3.5 *9.81) ?

• Physics -

yes.

• Physics -

The answer of 999.9 N was one I already tried, and it was not correct :(

• Physics -

oops. I should have given you more.
The density in the first part is the density of air.

volumeair*densityair*g
then the weight of the balloon has to include the weight of the helium (which is apparently not in the 3.5kg)
weightballoon=(3.5*g+volumehelium*densityhelium*g)
now is should work.

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