Yay, hopefully I can gather some pointers for this question. A lighter-than-air balloon and its load of passengers and ballast are floating stationary above the earth. Ballast is weight (of negligible volume) that can be dropped overboard to make the balloon rise. The radius of this balloon is 6.25m. Assuming a constant value of 1.29 kg/m^3 for the density of air, determine how much weight must be dropped overboard to make the balloons rise 105 m in 15.0s. I thinking this will involve Bernoulli's equation: P1+1/2pv^2 + pgy=P2+1/2pv^2 +pgy. Ok so P1 doesnt equal P2. Density should be same they cancel. P1+1/2v^2 +gy=P2 +1/2V^2 +gy. Now I'm stuck, P1 doesn't equal P2. y1 doesnt equal y2. Velocity is same? 105m/15s= 7m/s. Am I on the right track? :grumpy: Thanks!