A hydrogen -gas -filled balloon ofmass m can rise to a maximum height h above the earth's surface .On the earth's surface, potential energy of the balloon=

A hydrogen -gas -filled balloon ofmass m can rise to a maximum height

1.	A hydrogen -gas -filled balloon ofmass m can rise to a maximum height h above the earth's surface .On the earth's surface, potential energy of the balloon=
Answer» Solution :The potential energy of an object of MASS m , raised to a height H is mgh . Here mg=weight of the object =net downward force. But for a balloon ofmass m, the net downward force isnot mg. When it isstationary at a height h, the upward bouyancy balances the weight, the net downward force is ZERO. So the potential energy of the balloon at thatheight=0 , not mgh. this means thatthe total mechanical energy is zero, on the GROUND as well as at the height h. Thus , the law of CONSERVATION of energy is not violated.