Question

A balloon filled with helium rises against gravity increasing its potential energy. The speed of the balloon also increses as it rises. How do you reconcilethis with the law of consrvation of energy

Answer 1

Let m , V ρHe denote respectively the mass, volume and density of helium baloon and ρair be density of air

Volume V of baloon displaces volume V of air.

If the baloon rises to a height h, from s = ut + (1/2)at2, we, geAt h = (1/2)at2

So, as the baloon goes up, an equal volume of air comes down, increase in PE and KE of the baloon is at the cost of PE of air [which comes down].