Hi. There is a hot air ballon with total mass M. There is an upward lift force of 2Mg/3 but the balloon is accelerating downward at a rate of g/3. The passenger needs to make the balloon lighter and starts throwing things of. What fraction of the total weight must he drop overboard so that the balloon accelerates upward at a rate of g/2. I come up with the fact that the upward lift force must equal the weight plus the acceleration. But I get a wrong answear. The correct answear is 5/9. Can someone give me a hint to this problem please.