**Question:**

**A balloon filled with helium rises against gravity increasing its potential energy. The speed of the balloon also increases as it rises. How do you reconcile this with the law of conservation of mechanical energy? You can neglect the viscous drag of air and assume that the density of air is constant.**

**Solution:**

When the dragging viscous force of the air on the balloon is neglected, then the net buoyant force = vpg

Where v is the volume of air displaced

p is the net density upward

After calculation, it can be said that as the balloon goes up, the sum of kinetic energy and the potential energy of the balloon will be equal to change in potential energy in the air.