When the balloon is descending, the net force acting on it is given by Fnet =mg−B=ma, where B is the Buoyant force. Thus, B=mg−ma For the balloon to move upwards with the same acceleration a, a mass ∆m must be removed. The new net force equation becomes B−(m−∆m)g=(m−∆m)a mg−ma−(m−∆m)g=(m−∆m)a[ FromEq. (i)] ⇒∆m=
