Question

pg120. Question 4.5

Think about helium balloon. We know it is definitely floating upwards. Please use correct theoretical knowledge to explain (why / why not) balloon keep going up ?

( Imagine - Volume is not changing )

Good explanation from simple steps will be much appreciated.

Answer 1

In the Question Given that a hellium balloon will be definitely floating upwards.

Because the vertically upward buoyancy force due to atmospheric gases ( air) is higher than the vertically downward gravity force ( weight) of the balloon.

When the balloon floating on air , there will be two forces like gravity force in downward and other buoyancy force due to air in upward act on it.

Now, Let the volume of the balloon is, V= 1 m^{​​​​​​3}​​​ , contains hellium.

We know that the mass density of hellium gas is 0.179 kg/m^{​​​​​​3}​​​ and the air density , 1.2 kg/m^{​​​​​3}

So, the gravity force ,

( Where , g= acceleration due to gravity )

Or,

( Down ward direction)

The buoyancy force ,

Or,

( Upward direction )

So, the net force on the balloon is,

As the net force on the balloon is in the upward direction , the balloon goes upward.