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The problem states:

A paper ball is made which has a volume of V=0.1m3 and filled with the hot air of temperature T=340K. Outside temperature is T=290K while the pressure inside the ball and outside the ball is both p=100kPa. What should the mass of paper of the ball be that it would be able to arise in the air?

this question wasn't answered 3 years ago, I don't understand what mass changes here? do we have to calculate Archimede's force?

the molecular mass of the air M=29g/mole

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  • $\begingroup$ sorry I wanted to say this particular sphere, I will change the title $\endgroup$ – math boy Feb 6 at 18:28
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    $\begingroup$ Compute the mass of hot air + ball and compare it to the mass of an equal volume of cold air. $\endgroup$ – Bill Watts Feb 6 at 18:35
  • $\begingroup$ Hello! Please read How do I ask homework questions on Physics Stack Exchange? and edit your question accordingly. Thanks! $\endgroup$ – Jonas Feb 6 at 20:24
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I don't understand what mass changes here?

Hint: In order for the sphere to rise, the density of the sphere (paper + enclosed air) has to be less than the density of the air surrounding the sphere.

Hope this helps.

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The mass of the air inside the balloon plus the mass of the paper has to be less than that of an equal volume of outside air. Neglect the extra volume that the paper takes up.

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