1. The problem statement, all variables and given/known data Some hot air balloonists ﬁnd themselves accelerating downward with acceleration a at a moment when the mass of the balloon plus the passengers and cargo is M. They want to accelerate upwards at the same rate, so they toss out some of the cargo mass m (and maybe one or two of the balloonists). Determine m. 2. Relevant equations F=ma 3. The attempt at a solution Ok, so I think the force on the hot air balloon initially moving downward is either Ma or M(a+g). I thought it would just be the total mass times the acceleration given in the problem but gravity still has to be considered right? And once the cargo is thrown out the total mass will be (M-m). I guess I just don't know how to isolate m. This is a review question for my final exam and my professor doesn't give answers to anything. Any help would be greatly appreciated!