Suppose that a party balloon is spherical, has a radius of 16 centimetres and is filled with helium. Furthermore suppose that we do our experiment under standard atmospheric conditions, when the air density is \(\rho = 1.225 kg/m^3\). How many of these balloons should a 75 kilogram human carry in order to become airborne?

First you need to figure how much helium is the balloons. Each balloon's lift is reduced by the weight of the helium inside.

Once you know how much each balloon weighs, subtract that from the lifting power of the displaced air, which is 1.225kg * .01716 * 9.8N/kg, since each balloon occupies .01716 m^3

Now you know how many kg each balloon can lift; divide that into 75kg.

Thank you steve , please how do you know that each ballon occupies .01617m^3, please if possible give more precisions.

Thank you steve , please how do you know that each ballon occupies .01617m^3, please if possible give more precisions.

I find 0,002746744 which doesn´t make sens to me. How do I make it ? thanks

Simple. The question states that it is a spherical balloon. What is the volume of a sphere?

4/3 x pi x Radius (cube).

You already have the radius 0.16m (16 cm).

So now volume = 4/3x3.14x0.004096 = 0.01715 cubic meter

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I haven't understood how to solve it...

could u plz be a little more clear with the formulas u have used and ur calculations

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