So I know the volume of a hot air balloon and the temperatures of the air (ideal gas) inside the balloon and outside of it. I know the pressure of the air. And I need to find the Net force on the balloon and contents but neglecting the weight of the balloon itself. I thinkthere must be some way in the problem to use the ideal gas conditions P1*V1/T1 = P2*V2/T2 and that P=F/A to solve for a force. But since I don't have a V for the air outside I'm not sure how. I'm wondering if what's being meant by the 'net force' is the force that lifts the balloon up in which case I might have to find densities like in boyancy problems?